Internet DRAFT - draft-ietf-mip4-nemo-haaro
draft-ietf-mip4-nemo-haaro
Network Working Group A. Makela
Internet-Draft Aalto University, Department of
Intended status: Experimental Communications and
Expires: May 19, 2012 Networking (Comnet)
J. Korhonen
Nokia Siemens Networks
November 16, 2011
Home Agent assisted Route Optimization between Mobile IPv4 Networks
draft-ietf-mip4-nemo-haaro-07
Abstract
This document describes a Home Agent assisted Route Optimization
functionality to IPv4 Network Mobility Protocol. The function is
designed to facilitate optimal routing in cases where all nodes are
connected to a single Home Agent, thus the use case is Route
Optimization within single organization or similar entity. The
functionality adds the possibility to discover eligible peer nodes
based on information received from Home Agent, Network Prefixes they
represent, and how to establish a direct tunnel between such nodes.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 19, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction and motivations . . . . . . . . . . . . . . . . . 4
2. Terms and definitions . . . . . . . . . . . . . . . . . . . . 6
3. Mobile IPv4 route optimization between mobile networks . . . . 8
3.1. Maintaining route optimization information . . . . . . . . 9
3.1.1. Advertising route-optimizable prefixes . . . . . . . . 9
3.1.2. Route Optimization cache . . . . . . . . . . . . . . . 11
3.2. Return routability procedure . . . . . . . . . . . . . . . 13
3.2.1. Router keys . . . . . . . . . . . . . . . . . . . . . 15
3.2.2. Nonces . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.3. Updating Router keys and Nonces . . . . . . . . . . . 16
3.3. Mobile-Correspondent Router operations . . . . . . . . . . 17
3.3.1. Triggering Route Optimization . . . . . . . . . . . . 17
3.3.2. Mobile Router routing tables . . . . . . . . . . . . . 17
3.3.3. Inter-Mobile Router registration . . . . . . . . . . . 18
3.3.4. Inter-Mobile Router tunnels . . . . . . . . . . . . . 20
3.3.5. Constructing route-optimized packets . . . . . . . . . 21
3.3.6. Handovers and Mobile Routers leaving network . . . . . 21
3.4. Convergence and synchronization issues . . . . . . . . . . 22
4. Data compression schemes . . . . . . . . . . . . . . . . . . . 23
4.1. Prefix compression . . . . . . . . . . . . . . . . . . . . 24
4.2. Realm compression . . . . . . . . . . . . . . . . . . . . 26
4.2.1. Encoding of compressed realms . . . . . . . . . . . . 26
4.2.2. Searching algorithm . . . . . . . . . . . . . . . . . 27
4.2.3. Encoding example . . . . . . . . . . . . . . . . . . . 28
5. New Mobile IPv4 messages and extensions . . . . . . . . . . . 30
5.1. Mobile Router Route Optimization capability . . . . . . . 30
5.2. Route optimization reply . . . . . . . . . . . . . . . . . 31
5.3. Mobile-Correspondent authentication extension . . . . . . 32
5.4. Care-of address Extension . . . . . . . . . . . . . . . . 33
5.5. Route optimization prefix advertisement . . . . . . . . . 33
5.6. Home-Test Init message . . . . . . . . . . . . . . . . . . 35
5.7. Care-of-Test Init message . . . . . . . . . . . . . . . . 36
5.8. Home Test message . . . . . . . . . . . . . . . . . . . . 36
5.9. Care-of test message . . . . . . . . . . . . . . . . . . . 37
6. Special Considerations . . . . . . . . . . . . . . . . . . . . 38
6.1. NATs and stateful firewalls . . . . . . . . . . . . . . . 38
6.2. Handling of concurrent handovers . . . . . . . . . . . . . 40
6.3. Foreign Agents . . . . . . . . . . . . . . . . . . . . . . 40
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6.4. Multiple Home Agents . . . . . . . . . . . . . . . . . . . 40
6.5. Mutualness of Route Optimization . . . . . . . . . . . . . 41
6.6. Extensibility . . . . . . . . . . . . . . . . . . . . . . 42
6.7. Load Balancing . . . . . . . . . . . . . . . . . . . . . . 42
7. Scalability . . . . . . . . . . . . . . . . . . . . . . . . . 43
8. Example signaling scenarios . . . . . . . . . . . . . . . . . 43
8.1. Registration request . . . . . . . . . . . . . . . . . . . 43
8.2. Route optimization with return routability . . . . . . . . 44
8.3. Handovers . . . . . . . . . . . . . . . . . . . . . . . . 46
9. Protocol constants . . . . . . . . . . . . . . . . . . . . . . 47
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
11. Security Considerations . . . . . . . . . . . . . . . . . . . 49
11.1. Return Routability . . . . . . . . . . . . . . . . . . . . 50
11.2. Trust relationships . . . . . . . . . . . . . . . . . . . 50
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 50
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 51
13.1. Normative References . . . . . . . . . . . . . . . . . . . 51
13.2. Informative References . . . . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 52
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1. Introduction and motivations
Traditionally, there has been no method for route optimization in
Mobile IPv4 [RFC5944] apart from an early attempt
[I-D.ietf-mobileip-optim]. Unlike Mobile IPv6 [RFC3775], where Route
Optimization has been included from the start, with Mobile IPv4 route
optimization hasn't been addressed in a generalized scope.
Even though general route optimization may not be of interest in the
scope of IPv4, there are still specific applications for Route
Optimization in Mobile IPv4. This document proposes a method to
optimize routes between networks behind Mobile Routers, as defined by
NEMO [RFC5177]. Although NAT and the pending shortage of IPv4
addresses makes widespread deployment of end-to-end route
optimization infeasible, using Route Optimization from a Mobile
router to Mobile router is still a practical scenario. Note that the
method specified in this document is only for Route Optimization
between Mobile Routers; any network prefix not advertised by a Mobile
Router would still be routed via the Home Agent, although an MR could
advertise very large address spaces, e.g. by acting as an Internet
gateway.
A particular use case concerns setting up redundant yet economical
enterprise networks. Recently, a trend has emerged where customers
prefer to maintain connectivity via multiple service providers.
Reasons include redundancy, reliability, and availability issues.
These kinds of multi-homing scenarios have traditionally been solved
by using such technologies as multihoming BGP. However, a more
lightweight and economical solution is desirable.
From a service provider perspective a common topology for an
enterprise customer network consists of one to several sites
(typically headquarters and various branch offices). These sites are
typically connected via various Layer 2 technologies (ATM or Frame
relay PVCs), MPLS VPNs, or Layer 3 site-to-site VPNs. With a Service
Level Agreement, a customer can obtain a very reliable and well
supported intranet connectivity. However, compared to the cost of
"consumer-grade" broadband Internet access the SLA-guaranteed version
can be considered very expensive. These consumer-grade options,
however, are not reliable approach for mission-critical applications.
Mobile IP, especially Mobile Routers, can be used to improve
reliability of connectivity even when implemented over consumer-grade
Internet access. The customer becomes a client for a virtual service
provider, which does not take part in the actual access technology.
The service provider has a backend system and an IP address pool that
it distributes to customers. Access is provided by multiple,
independent, possibly consumer-grade ISPs, with Mobile IP providing
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seamless handovers if service from a specific ISP fails. The
drawback of this solution is that it creates a star topology; All
Mobile IP tunnels end up at the service provider hosted home agent,
causing heavy load at the backend. Route Optimization between mobile
networks addresses this issue, by taking network load off the home
agent and the backend.
An example network is pictured below:
+----------------------------+
| Virtual Operator Backend |
+------------+ +-----+
| Home Agent | | AAA |
+------------+---------+-----+
|
.--.
_(. `)
_( ISP `)_
( Peering `)
( ` . Point ) )
`--(_______)--'
____ / | \
/ | \
.--. .--. .--.
_( `. _( `. _( `.
( ISP A ) ( ISP B ) ( ISP C )
( ` . ) ) ( ` . ) ) ( ` . ) )
`--(___.-' `--(___.-' `--(___.-'
| ______/ \ /
| / \ /
| / \ /
+----+ +----+
|MR A| |MR B|
+----+ +----+
| |
.--. .--.
_( `. _( `.
( Site A ) ( Site B )
( ` . ) ) ( ` . ) )
`--(___.-' `--(___.-'
Virtual service provider architecture using NEMOv4
In this example case, the organization network consists of two sites
that are connected via 2 ISPs for redundancy reasons. Mobile IP
allows fast handovers without problems of multi-homing and BGP
peering between each individual ISP and the organization. The
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traffic however takes a non-optimal route through the virtual
operator backend.
Route optimization addresses this issue, allowing traffic between
Sites A and B to flow directly through ISP B's network, or in case of
a link failure, via the ISP peering point (such as MAE-WEST). The
backend will not suffer from heavy loads.
The specification in this document is meant to be experimental, with
the primary design goal is to limit the load on the backend to
minimum. Additional design goals include extensibility to a more
generalized scope, such as not requiring all MRs to be homed on the
same Home Agent. Experiences are mostly sought on applicability to
real-world operations, and protocol-specific issues such as signaling
scalability, interworking with other Mobile IP extensions not
specifically addressed in the document and behavior of end-user
applications over route-optimized paths.
The aforementioned use-case is the original application. Moving to
standards track should be considered after enough deployment
experience has been gathered. Besides the aforementioned issues,
additional elements that might require refinement based on real-world
experiences are delivery of information on networks managed by peer
Mobile Routers, conducting of the MR<->MR authentication, reaction
and recovery methods to connectivity breakdowns and other break-
before-make topology changes, keepalive timer intervals, formats of
signaling extensions, behavior in NAT/firewalled environment and the
prefix and realm compression algorithms.
2. Terms and definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Care-of Address (CoA)
RFC 5944 [RFC5944] defines Care-of Address as the termination
point of a tunnel toward a mobile node, for datagrams forwarded
to the mobile node while it is away from home. The protocol can
use two different types of care-of address: a "foreign agent
care-of address" which is an address of a foreign agent with
which the mobile node is registered, and a "co-located care-of
address", which is an externally obtained local address which
the mobile node has associated with one of its own network
interfaces. However, in the case of Network Mobility, foreign
agents are not used, so no foreign care-of addresses are used
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either.
Correspondent Router (CR)
RFC 5944 [RFC5944] defines a Correspondent node as a peer with
which a mobile node is communicating. Correspondent Router is a
peer Mobile Router which MAY also represent one or more entire
networks.
Home Address (HoA)
RFC 5944 [RFC5944] defines Home Address as an IP address that is
assigned for an extended period of time to a mobile node. It
remains unchanged regardless of where the node is attached to
the Internet.
Home Agent (HA)
RFC 5944 [RFC5944] defines Home Agent as a router on a mobile
node's home network which tunnels datagrams for delivery to the
mobile node when it is away from home, and maintains current
location information for the mobile node. For this application,
the "home network" sees limited usage.
Host Network Prefix
Network Prefix with the mask of /32. e.g. 192.0.2.254/32,
consisting of a single host.
Mobility Binding
RFC 5944 [RFC5944] defines Mobility Binding as the association
of Home Address with a Care-of address, along with the lifetime
remaining for that association.
Mobile Network Prefix RFC 5177 [RFC5177] defines Mobile Network
Prefix as the network prefix of the subnet delegated to a Mobile
Router as the Mobile Network.
Mobile Router (MR)
Mobile Router as defined by RFC 5177 [RFC5177] and RFC 5944
[RFC5944]. They define a Mobile Router as a mobile node that
can be a router that is responsible for the mobility of one or
more entire networks moving together, perhaps on an airplane, a
ship, a train, an automobile, a bicycle, or a kayak.
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Route Optimization Cache
Data structure maintained by Mobile Routers on possible
destinations for Route Optimization. Contains information (Home
Addresses) on potential Correspondent Routers and their
associated Mobile Networks.
Return Routability, RR
Procedure to bind a Mobile Router's Home Address to a Care-of
address on a Correspondent Router with a degree of trust.
| (Concatenation)
Some formulas in this specification use the symbol "|" to
indicate bytewise concatenation, as in A | B. This concatenation
requires that all of the octets of the datum A appear first in
the result, followed by all of the octets of the datum B.
First (size, input)
Some formulas in this specification use a functional form "First
(size, input)" to indicate truncation of the "input" data so
that only the first "size" bits remain to be used.
3. Mobile IPv4 route optimization between mobile networks
This section describes the changed functionality of Home Agent and
Mobile Router compared to the base NEMOv4 operation defined in
[RFC5177]. The basic premise is still the same; Mobile Routers, when
registering to the Home Agent, may inform the Home Agent of the
mobile network prefixes they are managing (explicit mode) or the Home
Agent already knows the prefix assignments. However, instead of
prefix <-> Mobile Router mapping information only remaining on the
Home Agent and the single Mobile Router, this information will now be
distributed to the other Mobile Routers as well.
The Home Agent-assisted Route Optimization is primarily intended for
helping to optimize traffic patterns between multiple sites in a
single organization or administrative domain; however, extranets can
also be reached with optimized routes, as long as all Mobile Routers
connect to the same Home Agent. The procedure aims to maintain
backwards compatibility; with legacy nodes or routers full
connectivity is always preserved even though optimal routing cannot
be guaranteed.
The scheme requires a Mobile Router to be able to receive messages
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from other Mobile Routers unsolicited - that is, without first
initiating a request. This behavior - accepting unsolicited messages
- is similar to the registration revocation procedure [RFC3543].
Many of the mechanisms are the same - including the fact that
advertising route optimization support upon registration implies
capability to receive registration requests and return routability
messages from other Mobile Routers.
Compared to IPv6, where Mobile Node <-> Correspondent node bindings
are maintained via Mobility Routing header and Home Address options,
Mobile IPv4 always requires the use of tunnels. Therefore, inter-
mobile-router tunnel establishment has to be conducted.
3.1. Maintaining route optimization information
During registration, a registering Mobile Router MAY request
information on route-optimizable network prefixes. The Mobile Router
MAY also allow redistribution of information on its managed network
prefixes regardless of whether they are explicitly registered or
already configured. These are indicated with a Mobile Router Route
Optimization capability extension; see Section 5.1. If the Home
Agent accepts the request for Route Optimization, this is indicated
with a Route Optimization Reply extension (Section 5.2) in the
registration reply.
Note that the redistribution of network prefix information from the
Home Agent happens only during the registration signaling. There are
no "routing updates" from the Home Agent except during re-
registrations triggered by handovers, registration timeouts, and
specific solicitation. The solicitation re-registration MAY occur if
a Correspondent Router receives a registration request from a unknown
Mobile Router (see Section 3.3.3).
3.1.1. Advertising route-optimizable prefixes
As noted, a NEMO-supporting Home Agent already maintains information
on which network prefixes are reachable behind specific Mobile
Routers. The only change to this functionality is that this
information can now be distributed to other Mobile Routers upon
request. This request is implied by including a Route Optimization
capability extension Route Optimization capability extension
(Section 5.1) and setting the 'R' bit.
When a Home Agent receives a registration request, standard
authentication and authorization procedures are conducted.
If registration is successful and the Route Optimization capability
information extension was present in the registration request, the
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reply message MUST include Route Optimization Reply extension
(Section 5.2) to indicate that Route Optimization Capability
extension was understood. Furthermore, the extension also informs
the Mobile Router whether NAT was detected between Home Agent and the
Mobile Router using the procedure in RFC 3519 [RFC3519], which is
based on the discrepancy between requester's indicated Care-of
address and packet's source address.
The reply message MAY also include one route optimization prefix
advertisement extension which informs the Mobile Router of existing
mobile network prefixes and the Mobile Routers that manage them, if
eligible for redistribution. The networks SHOULD be included in
order of priority, with the prefixes determined by policy as most
desirable targets for Route Optimization listed first. The extension
is constructed as shown in Section 5.5. The extension consists of a
list where each Mobile Router, identified by Home Address, is listed
with corresponding prefix(es) and their respective realm(s).
Each network prefix can be associated with a realm[RFC4282], usually
in the form 'organization.example.com'. Besides the routers in the
customer's own organization, the prefix list may also include other
Mobile Routers, e.g. a default prefix (0.0.0.0/0) pointing towards an
Internet gateway for Internet connectivity or additional prefixes
belonging to possible extranets. The realm information can be used
to make policy decisions on the Mobile Router, such as preferring
optimization within a specific realm only. Furthermore, the unique
realm information can be used to differentiate between overlapping
address spaces utilized by the same or different organizations
concurrently and adjusting forwarding policies accordingly.
In a typical scenario where Network Prefixes are allocated to Mobile
Routers connecting to a single Home Agent, the prefixes are usually
either continuous or at least very close to each other. Due to these
characteristics, an optional prefix compression mechanism is
provided. Another, optional, compression scheme is in use for realm
information, where realms often share the same higher-level domains.
These compression mechanisms are further explained in Section 4.
Upon receiving a registration reply with a Route Optimization prefix
advertisement extension, the Mobile Router SHALL insert the Mobile
Router Home Addresses included in the extension as host-prefixes to
the local Route Optimization Cache if they do not already exist. If
present, any additional prefixes information SHALL also be inserted
into the Route Optimization Cache.
The Mobile Router MAY discard entries from a desired starting point
onwards, due to memory or other policy related constraints. The
intention of listing the prefixes in order of priority is to provide
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implicit guidance for this decision. If the capacity of the device
allows, the Mobile Router SHOULD use information on all advertised
prefixes.
3.1.2. Route Optimization cache
Mobile routers supporting route optimization will maintain a Route
Optimization Cache.
The Route Optimization Cache contains mappings between potential
Correspondent Router HoA's, network(s) associated with each HoA,
information on reachability related to NAT and other divisions, and
Return Routability procedure-related information. The Cache is
populated based on information received from the Home Agent in Route
optimization prefix advertisements and in registration messages from
Correspondent Routers. Portions of the cache may also be configured
statically.
The Route Optimization Cache contains the following information for
all known Correspondent Routers. Note that some fields may contain
multiple entries. For example, during handovers, there may be both
old and new CoA's listed.
CR-HoA
Correspondent Router's Home Address. Primary key
identifying each CR.
CR-CoAs
Correspondent Router's Care-of Address(es). May be empty
if none known. Potential tunnel's destination address(es).
MR-CoAs
Mobile Router's Care-of Address(es) used with this
Correspondent Router. Tunnel's source address.
Tunnels
Tunnel interface(s) associated with this Correspondent
Router. The tunnel interface itself handles all the
necessary operations to keep the tunnel operational, e.g.
Sending keepalive messages required by UDP encapsulation.
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NAT states
A table of booleans, set for all pairs of potential MR-
CoA's and CR-CoA's which require NAT awareness and the
behavior is known, populated either statically or based on
discovery. If set to true, the MR can establish a UDP
tunnel towards the CR, using this pair of CoA's. A
received advertisement can indicate this to be set
initially false for all respective CR's CoA's. Affects
tunnel establishment direction; see Section 3.3.4 and the
registration procedure in deciding which Care-of-addresses
to include in the Care-of-address extension in registration
reply. If set to true, mandates use of UDP encapsulation.
RRSTATEs
Return routability state for each CR-HoA and MR-CoA pair.
States are INACTIVE, IN PROGRESS and ACTIVE. If state is
INACTIVE, return routability procedure must be completed
before forwarding route-optimized traffic. If state is IN
PROGRESS or ACTIVE, the information concerning this
Correspondent Router MUST NOT be removed from Route
Optimization Cache as long as a tunnel to the Correspondent
Router is established.
KRms
Registration management key for each CR-HoA - MR-CoA pair.
This field is only used if configured statically - if the
KRm was computed using Return Routability procedure, it is
calculated in-situ based on nonces and router key. If
configured statically, RRSTATE is permanently set to
ACTIVE.
Care-of nonce indices
If the KRm was established with Return Routability
procedure, contains the Care-of nonce index for each MR-CoA
- CR-HoA pair.
Care-of keygen token
If the KRm was established with Return Routability
procedure, contains the Care-of keygen token for each MR-
CoA - CR-HoA pair.
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Home nonce indices
If the KRm was established with Return Routability
procedure, contains the Home nonce index for each CR-HoA
Home keygen token
If the KRm was established with Return Routability
procedure, contains the Home keygen token for each CR-HoA.
Network Prefixes
A list of destination network prefixes reachable via this
Correspondent Router. Includes network and prefix length,
e.g. 192.0.2.0/25. Always contains at least a single
entry, the CR-HoA host network prefix in the form of
192.0.2.1/32.
Realms
Each prefix may be associated with a realm. May also be
empty, if realm is not provided by advertisement or
configuration.
Prefix_Valid
Boolean field for each prefix - CR-HoA pair, which is set
to true if this prefix's owner has been confirmed. The
Host Network Prefix consisting of the Correspondent Router
itself does need validation beyond Return Routability
procedure. For other prefixes, the confirmation is done by
soliciting the information from HA. Traffic for prefixes
which have unconfirmed ownership should not be routed
through the tunnel.
Information that is no longer valid due to expirations or topology
changes MAY be removed from the Route Optimization Cache as desired
by the Mobile Router.
3.2. Return routability procedure
The purpose of return routability procedure is to establish Care-of-
Address <-> Home Address bindings in a trusted manner. The return
routability procedure for Mobile IPv6 is described in [RFC3775]. The
same principles apply to the Mobile IPv4 version: two messages are
sent to the Correspondent Router's Home Address, one via Home Agent
using Mobile Router's Home Address, and the other directly from the
Mobile Router CoA, with two responses coming through same routes.
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Registration management key is derived from token information carried
on these messages. This registration management key (KRm) can then
be used to authenticate registration requests (comparable to Binding
Updates in Mobile IPv6).
The Return Routability procedure is a method provided by the Mobile
IP protocol to establish the KRm in a relatively lightweight fashion.
If desired, the KRm's can be configured to Mobile Routers statically,
or using a desired external secure key provisioning mechanism. If
KRm's are known to the Mobile Routers via some other mechanism, the
Return Routability procedure can be skipped. Such provisioning
mechanisms are out of scope for this document.
The main assumption on traffic patterns is that the Mobile Router
that initiates the RR procedure can always send outbound messages,
even when behind NAT or firewall. This basic assumption made for NAT
Traversal in [RFC3519] is also applicable here. In case the
Correspondent Router is behind such obstacles, it receives these
messages via the reverse tunnel to CR's Home Address, thus any
problem regarding the CR's connectivity is addressed during the
registration to the Home Agent.
The Return Routability procedure consists of four Mobile IP messages:
Home Test Init, Care-of Test Init, Home Test and Care-of Test. They
are constructed as shown in Section 5.6 through Section 5.9. If the
Mobile Router has included the Mobile Router Route Optimization
capability extension in its Registration Request, it MUST be able to
accept Return Routability messages. The messages are delivered as
Mobile IP signaling packets. The destination address of HoTI and
CoTI messages is set to Correspondent Router's HoA with the sources
being MR's home and care-of-address, respectively.
The return routability procedure begins with the Mobile Router
sending HoTI and CoTI messages, each containing a (different) 64-bit
random value, the cookie. The cookie is used to bind specific
signaling exchange together.
Upon receiving the HoTI or CoTI message the Correspondent Router MUST
have a secret Kcr and nonce. If it does not have this material yet,
it MUST produce it before continuing with the return routability
procedure.
Correspondent Router responds to HoTI and CoTI messages by
constructing HoT and CoT messages, respectively, as replies. The HoT
message contains home init cookie, current home nonce index and home
keygen token. The CoT message contains care-of init cookie, current
care-of nonce index and care-of keygen token.
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The Home Keygen token is constructed as follows:
Home keygen token = First (64, HMAC_SHA1 (Kcr, (home address | nonce
| 0)))
The Care-of Keygen token is constructed as follows:
Care-of keygen token = First (64, HMAC_SHA1 (Kcr, (Care-of address |
nonce | 1)))
Note that the Care-of address in this case is the source address of
the received CoTI message packet. The address may have changed in-
transit due to network address translation. This does not affect
registration process; subsequent registration requests are expected
to arrive from the same translated address.
Return Routability procedure SHOULD be initiated when the Route
Optimization Cache's RRSTATE field for the desired Care-of Address
with target Correspondent Router is INACTIVE. If the state was
INACTIVE, the state MUST be set to IN PROGRESS when Return
Routability procedure is initiated. In case of handover occurring,
the Mobile Router SHOULD only send a CoTI message to obtain a new
care-of keygen token; The home keygen token may still be valid. If
the reply to a registration indicates that one or both of the tokens
has expired, the RRSTATE MUST be set to INACTIVE. The Return
Routability procedure may then be restarted as needed.
Upon completion of Return Routability procedure, the Routing
Optimization Cache's RRSTATE field is set to ACTIVE, allowing for
registration requests to be sent. The Mobile Router will establish a
registration management key KRm by default using SHA1 hash algorithm:
KRm = SHA1 (home keygen token | care-of keygen token)
When de-registering (by setting time to zero), care-of keygen token
is not used. Instead the Registration management key is generated as
follows:
KRm = SHA1 (home keygen token)
Like in Mobile IPv6, the Correspondent Router does not maintain any
state for the Mobile Router until after receiving a registration
request.
3.2.1. Router keys
Each Mobile Router maintains a 'correspondent router key', Kcr, which
MUST NOT be shared with any other entity. Kcr is used for
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authenticating peer Mobile Routers in the situation where a mobile
router is acting as a CR. This is analogous to node key, Kcn, in
Mobile IPv6. A Correspondent Router uses its router key to verify
that the keygen tokens sent by a peer Mobile Router in a registration
request are the CR's own. The router key MUST be a random number, 16
octets in length, generated with a good random number generator
[RFC4086].
The Mobile Router MAY generate a new key at any time to avoid
persistent key storage. If desired, it is RECOMMENDED to expire the
keys in conjunction with nonces; see Section 3.2.3.
3.2.2. Nonces
Each Mobile Router also maintains one or more indexed nonces. Nonces
SHOULD be generated periodically with a good random number generator
[RFC4086]. The Mobile Router may use the same nonces with all Mobile
Routers. Nonces MAY be of any length, with the RECOMMENDED length
being 64 bits.
3.2.3. Updating Router keys and Nonces
The router keys and nonce updating guidelines are similar to ones in
Mobile IPv6. Mobile Routers keep both the current nonce and small
set of valid previous nonces whose lifetimes have not expired yet.
Nonce should remain valid for at least MAX_TOKEN_LIFETIME (see
Section 9) seconds after it has first been used in constructing a
return routability response. However, the correspondent router MUST
NOT accept nonces beyond MAX_NONCE_LIFETIME seconds (see Section 9)
after the first use. As the difference between these two constants
is 30 seconds, a convenient way to enforce the above lifetimes is to
generate a new nonce every 30 seconds. The node can then continue to
accept keygen tokens that have been based on the last 8
(MAX_NONCE_LIFETIME / 30) nonces. This results in keygen tokens
being acceptable MAX_TOKEN_LIFETIME to MAX_NONCE_LIFETIME seconds
after they have been sent to the mobile node, depending on whether
the token was sent at the beginning or end of the first 30 second
period. Note that the correspondent node may also attempt to
generate new nonces on demand, or only if the old nonces have been
used. This is possible, as long as the correspondent node keeps
track of how long a time ago the nonces were used for the first time,
and does not generate new nonces on every return routability request.
If Kcr is being updated, the update SHOULD be done at the same time
as nonce is updated. This way, nonce indexes can be used to refer to
both Kcr's and nonces.
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3.3. Mobile-Correspondent Router operations
This section deals with the operation of Mobile and Correspondent
Routers performing route optimization. Note that in the context of
this document all routers work as both Mobile Router and
Correspondent Router. The term "Mobile Router" applies to the router
initiating the Route Optimization procedure, and "Correspondent
Router" indicates the peer router.
Especially compared to Mobile IPv6 route optimization there are two
issues that are different regarding IPv4. First of all, since Mobile
IPv4 always uses tunnels, there must be a tunnel established between
MR and CR's Care-of addresses. The Correspondent Router learns of
Mobile Router's Care-of address as it is provided by the Registration
Request. The Mobile Router learns the Correspondent Router's Care-of
address by a new extension, "Care-of Address", in the registration
reply. The second issue is a security consideration: in a
registration request, the Mobile Router claims to represent an
arbitrary IPv4 network. If the CR has not yet received this
information (HoA <-> Network prefix), it SHOULD perform a re-
registration to the Home Agent to verify the claim.
An additional aspect is that Mobile Router MAY use a different Care-
of-Address for different Correspondent Routers (and Home Agent).
This is useful in situations where the network provides only partial-
mesh connectivity, and specific interfaces must be used to reach
specific destinations. In addition, this allows for load balancing.
3.3.1. Triggering Route Optimization
Since each Mobile Router knows the eligible route-optimizable
networks, the route optimization between all Correspondent Routers
can be established at any time; however a better general practice is
to conduct Route Optimization on-demand only. It is RECOMMENDED to
start Route optimization only when sending a packet that originates
from a local managed network (and the network is registered as route
optimizable) and whose destination address falls within the network
prefixes of the Route Optimization Cache. With a small number of
Mobile Routers, such on-demand behavior may not be necessary and
full-mesh route-optimization may be in place constantly.
3.3.2. Mobile Router routing tables
Each Mobile Router maintains a routing table. In a typical
situation, the Mobile Router has one or more interface(s) to the
local networks, one or more interface(s) to wide-area networks (such
as provided by ISPs), and a tunnel interface to the Home Agent.
Additional tunnel interfaces become activated as Route Optimization
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is being performed.
The routing table SHOULD typically contain Network Prefixes managed
by Correspondent Routers associated with established route-optimized
tunnel interfaces. A default route MAY point to the reverse tunnel
to the Home Agent if not overridden by prefix information. The
routing table MAY also include additional routes if required by
tunneling implementation.
The route for the Home Address of Correspondent Router SHOULD also be
pointing towards the tunnel taking the optimized path.
If two prefixes overlap each other, e.g. 192.0.2.128/25 and
192.0.2.128/29, the standard longest match rule for routing is in
effect. However, overlapping private address SHOULD be considered an
error situation. Any aggregation for routes in private address space
SHOULD be conducted only at HA.
3.3.3. Inter-Mobile Router registration
If route optimization between a Mobile Router and a Correspondent
Router is desired, either the Return Routability procedure must have
been performed ( See Section 3.2), or key KRm must be pre-shared
between the Mobile and Correspondent Router. If either condition
applies, a Mobile Router MAY send a registration request to the
Correspondent Router's HoA from the desired interface.
The registration request's source address and Care-of address field
are set to the address of the desired outgoing interface on the
Mobile Router. The address MAY be same as the Care-of address used
with the Home Agent. The Home Agent field is set to the Home Agent
of the Mobile Router. The registration request MUST be sent to (have
a destination address of) the Home Address of the Correspondent
Router. The registration request MUST include a Mobile-Correspondent
Authentication extension defined in Section 5.3 and SHOULD include a
Mobile Network Request Extension defined in [RFC5177]. If present,
the Mobile Network Request Extension MUST contain the network
prefixes, as if registering in explicit mode. If timestamps are
used, the Correspondent Router MUST check the identification field
for validity. The Authenticator field is hashed with the key KRm.
The Correspondent Router replies to the request with a Registration
Reply. The registration reply MUST include a Mobile-Correspondent
Authentication extension defined in Section 5.3 and, if Mobile
Network Request Extension was present in the request, a Mobile
Network Acknowledgement extension.
The encapsulation can be set as desired, except in the case where the
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Route Optimization Cache Entry has NAT entries for the Correspondent
Router, or the Mobile Router itself is known to be behind NAT or
firewall. If either of the conditions apply, the Registration
Request MUST specify UDP encapsulation. It is RECOMMENDED to always
use UDP encapsulation to facilitate detection of path failures via
keepalive mechanism.
The Correspondent Router first checks the registration request's
authentication against Kcr and nonce indexes negotiated during Return
Routability procedure. This ensures that the registration request is
coming from a correct Mobile Router. If the check fails, an
appropriate registration reply code is sent (see Section 10). If the
failure is due to nonce index expiring, the Mobile Router sets
RRSTATE for the CR to INACTIVE. Return routability procedure MAY
then be initiated again.
If the check passes, the Correspondent Router MUST then check it's
Route Optimization Cache for whether the Mobile Router exists is
associated with the prefixes included in the request (Prefixes are
present and Flag HA is true for each prefix). Note that the
viewpoint is always local; the Correspondent Router compares CR-HoA
entries against the MR's Home Address - from the CR's perspective the
Mobile Router is also a "Correspondent Router".
If the check against the cache fails, the Correspondent Router SHOULD
send a re-registration request to Home Agent with the 'S'
(solicitation) bit set, thus obtaining the latest information on
Network Prefixes managed by the incoming Mobile Router. If, even
after this update, the prefixes still don't match, the reply's Mobile
Network Acknowledgement code MUST be set to "MOBNET_UNAUTHORIZED".
The registration MAY also be rejected completely. This verification
is done to protect against Mobile Routers claiming to represent
arbitrary networks; however, since the Home Agent is assumed to
provide trusted information, it can authorize the Mobile Router's
claim. If the environment itself is considered trusted, the
Correspondent Router can, as a policy, accept registrations without
this check; however, this is NOT RECOMMENDED as a general practice.
If the prefixes match, the Correspondent Router MAY accept the
registration. If the CR chooses to accept, the CR MUST check if a
tunnel to the Mobile Router already exists. If the tunnel does NOT
exist or has wrong endpoints (CoAs), a new tunnel MUST be established
and the Route Optimization Cache updated. The reply MUST include a
list of eligible care-of-addresses (see Section 5.4), with which the
Mobile Router may establish a tunnel. The reply MUST also include
Mobile-Correspondent Authentication extension (See Section 5.3).
Upon receiving the registration reply, the Mobile Router MUST check
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if a tunnel to the Correspondent Router already exists. If the
tunnel does NOT exist, or has wrong endpoints (CoAs), a new tunnel
MUST be established and Route Optimization Cache updated. This is
covered in detail in Section 3.3.4.
The Correspondent Router's routing table MUST be updated to indicate
that the Mobile Router's networks are reachable via the direct tunnel
to the Mobile Router.
After the tunnel is established, the Mobile Router MAY update it's
routing tables to reach all Correspondent Router's Prefixes via the
tunnel, although it is RECOMMENDED to wait for the Correspondent
Router to perform it's own, explicit registration. This is primarily
a policy decision depending on the network environment. See
Section 6.5.
Due to the fact that the route optimization procedures may occur
concurrently at two Mobile Routers, each working as each other's
Correspondent Router, there may be a situation where two routers are
attempting to establish separate tunnels between them at the same
time. If a router with a smaller Home Address (meaning a normal 32-
bit integer comparison treating IPv4 addresses as 32-bit unsigned
integers) receives a registration request (in CR role) while its own
registration request (sent in MR role) is pending, the attempt should
be accepted with reply code "concurrent registration" (Value TBA_S1).
If receiving such an indication, the recipient SHOULD consider the
registration a success, but only act on it once the peer has
completed it's own registration.
3.3.4. Inter-Mobile Router tunnels
Inter-Mobile Router tunnel establishment follows establishing
standard reverse tunnels to the Home Agent. The registration request
to Correspondent Router includes information on the desired
encapsulation. It is RECOMMENDED to use UDP encapsulation. In the
cases of GRE [RFC2784], IP over IP [RFC2003] or minimal encapsulation
[RFC2004] no special considerations regarding the reachability are
necessary; The tunnel has no stateful information; The packets are
simply encapsulated within the GRE, IP, or minimal header.
The tunnel origination point for the Correspondent Router is its
Care-of Address, not the Home Address where the registration requests
were sent. This is different from creation of the Reverse Tunnel to
Home Agent, which reuses the channel from registration signaling.
Special considerations rise from using UDP encapsulation, especially
in cases where one of the Mobile Routers is located behind NAT or
firewall. A deviation from RFC 3519 [RFC3519] is that keepalives
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should be sent both from ends of the tunnel to detect path failures
after the initial keepalive has been sent - this allows both MR and
CR to detect path failures.
The initial UDP keepalive SHOULD be sent by the MR. Only after first
keepalive is successfully completed, SHOULD the tunnel be considered
eligible for traffic. If reply to the initial keepalive is not
received, the MR may opt to attempt sending the keepalive with other
Care-of addresses provided by the registration reply to check whether
they provide better connectivity, or if all of these fail, perform a
re-registration via alternative interface, or deregister completely.
See Section 6.1. Once the initial keepalive packet has reached the
CR and reply has been sent, the CR MAY start sending its own
keepalives.
The original specification for UDP encapsulation suggests a keepalive
interval default of 110 seconds. However, to provide fast response
time and switching to alternate paths, it is RECOMMENDED, if power
and other constraints allow, to use considerably shorter periods,
adapting to the perceived latency as needed. However, the maximum
amount of keepalives should at no point exceed MAX_UPDATE_RATE times
per second. The purpose of keepalive is not to keep NAT or firewall
mappings in place, but serve as a mechanism to provide fast response
in case of path failures.
If both the Mobile Router and the Correspondent Router are behind
separate NATs, route optimization cannot be performed between them.
Possibilities to set up mutual tunneling when both routers are behind
NAT, are outside the scope of this document. However, some of these
issues are addressed in Section 6.1.
The designations "MR" and "CR" only apply to the initial tunnel-
establishment phase. Once a tunnel is established between two
routers, either of them can opt to either tear down the tunnel or
perform a handover. Signaling messages have to be authenticated with
valid KRm.
3.3.5. Constructing route-optimized packets
All packets received by the Mobile Router are forwarded using normal
routing rules according to the routing table. There are no special
considerations when constructing the packets, the tunnel interface's
own processes will encapsulate any packet automatically.
3.3.6. Handovers and Mobile Routers leaving network
Handovers and connection breakdowns can be categorized as either
ungraceful or graceful, also known as "break-before-make" (bbm) and
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"make-before-break" (mbb) situations.
As with establishment, the "Mobile Router" discussed here is the
router wishing to change connectivity state, "Correspondent Router"
being the peer.
When a Mobile Router wishes to join its home link, it SHOULD, in
addition to sending the registration request to the Home Agent with
lifetime set to zero, also send such a request to all known
Correspondent Routers to their Home Address. The Correspondent
Router(s), upon accepting this request and sending the reply, will
check whether Route Optimization Cache contains any prefixes
associated with the requesting Mobile Router. These entries should
be removed and routing table updated accordingly (traffic for the
prefixes will be forwarded via the Home Agent again). The tunnel
MUST then be destroyed. A short grace period SHOULD be used to allow
possible in-transit packets to be received correctly.
In the case of a handover, the Correspondent Router simply needs to
update the tunnel's destination to the Mobile Router's new Care-of
Address. Mobile Router SHOULD keep accepting packets from both old
and new care-of Addresses for a short grace period, typically on the
order of ten seconds. In the case of UDP encapsulation, it is
RECOMMENDED to use same port numbers for both registration signaling
and tunneled traffic if possible. The initial keepalive message sent
by the MR will verify that direct connectivity exists between MR and
CR - if the keepalive fails, the MR SHOULD attempt alternate paths.
If the Mobile Router was unable to send the re-registration request
before handover, it MUST send it immediately after handover has been
completed and tunnel with the Home Agent is established. Since
Care-of Address(es) changing invalidates the Krm, it is RECOMMENDED
to conduct partial Return Routability by sending CoTI message via the
new Care-of-Address and obtaining new care-of keygen token. In all
cases, necessary tokens have also to be acquired if the existing ones
have expired.
If a reply is not received for a registration request to a
Correspondent Router, any routes to the network prefixes managed by
the Correspondent Router MUST be removed from the routing table, thus
causing the user traffic to be forwarded via the Home Agent.
3.4. Convergence and synchronization issues
The information the Home Agent maintains on Mobile Network prefixes
and the Mobile Routers' Route Optimization Caches do not need to be
explicitly synchronized. This is based on the assumption that at
least some of the traffic between nodes inside mobile networks is
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always bidirectional. If using on-demand route optimization, this
also implies that when a node in a mobile network talks to a node in
another mobile network, if the initial packet does not trigger Route
Optimization, the reply packet will.
Consider a situation with three mobile networks, A, B, C handled by
three Mobile Routers, MR A, MR B and MR C respectively. If they
register to a Home Agent in this order, the situation goes as
follows:
MR A registers and receives no information on other networks from HA,
as no other MR has registered yet.
MR B registers and receives information on mobile network A being
reachable via MR A.
MR C registers and receives information on both of the other mobile
networks.
If a node in mobile network C is about to send traffic to mobile
network A, the route optimization is straightforward; MR C already
has network A in its Route Optimization Cache. Thus, packet
transmission triggers Route Optimization towards MR A. When MR C
registers to MR A (after Return Routability procedure is completed),
MR A does not have information on mobile network C; Thus it will
perform a re-registration to the Home Agent on-demand. This allows
MR A to verify that MR C is indeed managing network C.
If a node in mobile network B sends traffic to mobile network C, MR B
has no information on network C. No route optimization is triggered.
However, when the node in network C replies and the reply reaches MR
C, route optimization happens as above. Further examples of
signaling are in Section 8.
Even in the very rare case of completely unidirectional traffic from
an entire network, the re-registrations to the Home Agent caused by
timeouts will eventually cause convergence. However, this should be
treated as a special case.
Note that all Mobile Routers are connected to same Home Agent. For
possibilities concerning multiple Home Agents, see Section 6.4
4. Data compression schemes
This section defines the two compression formats used in Route
Optimization Prefix Advertisement extensions.
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4.1. Prefix compression
The prefix-compression is based on the idea that prefixes usually
share common properties. The scheme is simple delta-compression. In
the prefix information advertisement, Section 5.5, the D bit
indicates whether receiving a "master" or a "delta" prefix. This,
combined with the Prefix Length information, allows for compression
and decompression of prefix information.
If D=0, what follows in the "Prefix" field are bits 1..n of the new
master prefix, where n is PLen. This is rounded up to nearest full
octet. Thus, prefix lengths of /4 and /8 take 1 octet, /12 and /16
take 2 octets, /20 and /24 three, and larger than that full 4 octets.
If D=1, what follows in the "Prefix" field are bits m..PLen of the
prefix, where m is the first changed bit of previous master prefix,
with padding from the master prefix filling the field to full octet.
Maximum value of Plen-m is 8 (that is, delta MUST fit into one
octet). If this is not possible, a new master prefix has to be
declared. If the prefixes are equal, for example in the case where
same prefix appears in multiple realms, then one octet is still
encoded, consisting completely of padding from the master prefix.
Determining the order of prefix transmission should be based on
saving maximum space during transmission.
Example of compression and transmitted data, where network prefixes
192.0.2.0/28, 192.0.2.64/26 and 192.0.2.128/25 are transmitted are
illustrated in Figure 1. Because of the padding to full octets,
redundant information is also sent. The bit-patterns being
transmitted are:
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=+= shows the prefix mask
--- shows the master prefix for delta coded prefixes
192.0.2.0/28, D=0
0 1 2 3
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|1|0|0|0|0|0|0|.|0|0|0|0|0|0|0|0|.|0|0|0|0|0|0|1|0|.|0|0|0|0|0|0|0|0|
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+-+-+-+-+
^ ^
+---------------------------- encoded ------------------------------+
^ ^
+-pad-+
192.0.2.64/26, D=1
0 1 2 3
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-------------------------------------------------------------+-+-+-+-+
|1|1|0|0|0|0|0|0|.|0|0|0|0|0|0|0|0|.|0|0|0|0|0|0|1|0|.|0|1|0|0|0|0|0|0|
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+-+-+-+-+-+-+
^ ^
+--- encoded ---+
^ ^
+-- padding --+
192.0.2.128/25, D=1
0 1 2 3
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-------------------------------------------------------------+-+-+-+-+
|1|1|0|0|0|0|0|0|.|0|0|0|0|0|0|0|0|.|0|0|0|0|0|0|1|0|.|1|0|0|0|0|0|0|0|
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+-+-+-+-+-+-+-+
^ ^
+--- encoded ---+
^ ^
+- padding -+
Figure 1: Prefix Compression Example
First prefix, 192.0.2.0/28, is considered a master prefix and is
transmitted in full. The PLen of 28 bits determines that all four
octets must be transmitted. If the prefix would have been e.g.
192.0.2.0/24, three octets would have sufficed since 24 bits fit into
3 octets.
For the following prefixes, the D=1. Thus, they are deltas of the
previous prefix where D was zero.
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192.0.2.64/26 includes bits 19-26 (full octet). Bits 19-25 are
copied from master prefix, but bit 26 is changed to 1. The final
notation in binary is "1001", or 0x09.
192.0.2.128/25 includes bits 18-25 (full octet). Bits 18-24 are
copied from master prefix, but bit 25 is changed to 1. The final
notation in binary is "101", or 0x05.
The final encoding thus becomes:
+----------------+--------+-+---------------------+
| Prefix | Plen |D| Transmitted Prefix |
+----------------+--------+-+---------------------+
| 192.0.2.0/28 | 28 |0| 0xc0 0x00 0x02 0x00 |
| 192.0.2.64/26 | 26 |1| 0x09 |
| 192.0.2.128/25 | 25 |1| 0x05 |
+----------------+--------+-+---------------------+
It should be noted that in this case the order of prefix transmission
would not affect compression efficiency. If prefix 192.0.2.128/25
would have been considered the master prefix and the others as deltas
instead, the resulting encoding still fits into one octet for the
subsequent prefixes. There would be no need to declare a new master
prefix.
4.2. Realm compression
4.2.1. Encoding of compressed realms
In order to reduce the size of messages, the system introduces a
realm compression scheme, which reduces the size of realms in a
message. The compression scheme is a simple dynamically updated
dictionary based algorithm, which is designed to compress arbitrary
length text strings. In this scheme, an entire realm, a single label
or a list of labels may be replaced with an index to a previous
occurrence of the same string stored in the dictionary. The realm
compression defined in this specification was inspired by the RFC
1035 [RFC1035] DNS domain name label compression. Our algorithm is,
however, improved to gain more compression.
When compressing realms, the dictionary is first reset and does not
contain a single string. The realms are processed one by one so the
algorithm does not expect to see them all or the whole message at
once. The state of the compressor is the current content of the
dictionary. The realms are compressed label by label or as a list of
labels. The dictionary can hold a maximum of 128 strings, after
that, a rollover MUST occur and existing contents will be
overwritten. Thus, when adding the 129th string into the dictionary,
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the first entry of the dictionary MUST be overwritten and the index
of the new string will become 0.
The encoding of an index to the dictionary or an uncompressed run of
octets representing a single label has purposely been made simple and
the whole encoding works on an octet granularity. The encoding of an
uncompressed label takes the form of a one octet:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-=================-+-+-+-+
|0| LENGTH | 'length' octets long string.. |
+-+-+-+-+-+-+-+-+-+-+-+-=================-+-+-+-+
This encoding allows label lengths from 1 to 127 octets. A label
length of zero (0) is not allowed. The "label length" tag octet is
then followed by up to 127 octets of the actual encoded label string.
The index to the dictionary (the "label index" tag octet) takes the
form of a one octet:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1| INDEX |
+-+-+-+-+-+-+-+-+
The above encodings do not allow generating an output octet value of
zero (0). The encapsulating Mobile IPv4 extension makes use of this
property and uses the value of zero (0) to mark the end of compressed
realm or to indicate an empty realm. It is also possible to encode
the complete realm using only "label length" tags. In this case no
compression takes place. This allows the sender to skip compression,
for example to reduce computation requirements when generating
messages. However, the receiver MUST always be prepared to receive
compressed realms.
4.2.2. Searching algorithm
When compressing the input realm, the dictionary is searched for a
matching string. If no match could be found, the last label is
removed from the right-hand side of the used input realm. The search
is repeated until the whole input realm has been processed. If no
match was found at all, then the first label of the original input
realm is encoded using the "label length" tag and the label is
inserted into the dictionary. The previously described search is
repeated with the remaining part of the input realm, if any. If
nothing remains, the realm encoding is complete.
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When a matching string is found in the dictionary the matching part
of the input realm is encoded using the "label index" tag. The
matching part of the input realm is removed and the search is
repeated with the remaining part of the input realm, if any. If
nothing remains, the octet value of zero (0) is inserted to mark the
end of encoded realm.
The search algorithm also maintains the "longest non-matching string"
for each input realm. Each time the search in dictionary fails and a
new label gets encoded using the "label length" tag and inserted into
the dictionary, the "longest non-matching string" is concatenated by
this label including the separating "." (dot, i.e. Hexadecimal
0x2e). When a match is found in the dictionary the "longest non-
matching string" is reset (i.e. Emptied). Once the whole input
realm has been processed and encoded, all possible suffixes longer
than one label are taken from the string and inserted into the
dictionary.
4.2.3. Encoding example
This section shows an example how to encode a set of realms using the
specified realm compression algorithm. For example, a message might
need to compress the realms "foo.example.com", "bar.foo.example.com",
"buz.foo.example.org", "example.com" and "bar.example.com.org". The
following example shows the processing of input realms on the left
side and the contents of the dictionary on the right hand side. The
example uses hexadecimal representation of numbers.
COMPRESSOR: DICTIONARY:
1) Input "foo.example.com"
Search("foo.example.com")
Search("foo.example")
Search("foo")
Encode(0x03,'f','o','o') 0x00 "foo"
+-> "longest non-matching string" = "foo"
Search("example.com")
Search("example")
Encode(0x07,'e','x','a','m','p','l','e') 0x01 "example"
+-> "longest non-matching string" = "foo.example"
Search("com")
Encode(0x03,'c','o','m') 0x02 "com"
+-> "longest non-matching string" = "foo.example.com"
0x03 "foo.example.com"
0x04 "example.com"
Encode(0x00)
2) Input "bar.foo.example.com"
Search("bar.foo.example.com")
Search("bar.foo.example")
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Search("bar.foo"
Search("bar")
Encode(0x03,'b','a','r') 0x05 "bar"
+-> "longest non-matching string" = "bar"
Search("foo.example.com") -> match to 0x03
Encode(0x83)
+-> "longest non-matching string" = NUL
Encode(0x00)
3) Input "buz.foo.example.org"
Search("buz.foo.example.org")
Search("buz.foo.example")
Search("buz.foo")
Search("buz")
Encode(0x03,'b','u','z') 0x06 "buz"
+-> "longest non-matching string" = "buz"
Search("foo.example.org")
Search("foo.example")
Search("foo") -> match to 0x00
Encode(0x80)
+-> "longest non-matching string" = NUL
Search("example.org")
Search("example") -> match to 0x01
Encode(0x81)
+-> "longest non-matching string" = NUL
Search("org")
Encode(0x03,'o','r','g') 0x07 "org"
+-> "longest non-matching string" = "org"
Encode(0x00)
4) Input "example.com"
Search("example.com") -> match to 0x04
Encode(0x84)
Encode(0x00)
5) Input "bar.example.com.org"
Search("bar.example.com.org")
Search("bar.example.com")
Search("bar.example")
Search("bar") -> match to 0x05
Encode(0x85)
Search("example.com.org")
Search("example.com") -> match to 0x04
Encode(0x84)
Search("org") -> match to 0x07
Encode(0x87)
Encode(0x00)
As can be seen from the example, due the greedy approach of encoding
matches, the search algorithm and the dictionary update function is
not the most optimal one. However, we do not claim the algorithm
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would be the most efficient. It functions efficiently enough for
most inputs. In this example, the original input realm data was 79
octets and the compressed output excluding the end mark is 35 octets.
5. New Mobile IPv4 messages and extensions
This section describes the construction of all new information
elements.
5.1. Mobile Router Route Optimization capability
This skippable extension MAY be sent by a Mobile Router to a Home
Agent in the registration request message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-type |A|R|S|O| Rsvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional Mobile Router HoA ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type TBA_T1. Skippable; If Home Agent does not support route
optimization advertisements, it can ignore this request and
simply not include any information in the reply. "Short"
extension format.
Sub_Type 1
Reserved Set to zero, MUST be ignored on reception.
A Advertise my networks. If 'A' bit is set, the Home Agent
is allowed to advertise the networks managed by this Mobile
Router to other Mobile Routers. This also indicates that
the Mobile Router is capable of receiving route
optimization registration requests. In effect, this allows
the Mobile Router to work in Correspondent Router role.
R Request mobile network information. If 'R' bit is set, the
Home Agent MAY respond with information about mobile
networks in the same domain.
S Soliciting prefixes managed by a specific Mobile Router.
The Mobile Router is specified in the Optional Mobile
Router HoA field.
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O Explicitly specifying the requesting Router is only able to
initiate outgoing connections, not accept any incoming
ones, due to NAT device, stateful firewall, or similar
issue on any interface. This is reflected by the Home
Agent in the reply, and distributed in Prefix
Advertisements to other Mobile Routers.
Optional Mobile Router HoA
Solicited Mobile Router's Home Address. This field is only
included if flag 'S' is set.
5.2. Route optimization reply
This non-skippable extension MUST be sent by a Home Agent to a Mobile
Router in the registration reply message, if Mobile Router indicated
support for Route Optimization in registration message and Home Agent
supports Route Optimization.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Type |O|N|S| Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type TBA_T2 (Non-skippable), "short" extension format
Sub-Type 1
O The 'O' flag in Mobile Router Route Optimization capability
extension was set during registration.
N Presence of NAT was detected by Home Agent. This informs
the Mobile Router that it is located behind NAT. The
detection procedure is specified in RFC 3519 [RFC3519], and
is based on the discrepancy between registration packet's
source address and indicated Care-of Address. The Mobile
Router can use this information to make decisions about
Route Optimization strategy.
S Responding to a solicitation. If 'S' bit was present in
Mobile router Route optimization capability extension
(Section 5.1), this is set, otherwise unset.
The Reply code indicates whether Route Optimization has been
accepted. Values of 0..15 indicate assent and values 16..63 indicate
Route Optimization is not done.
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0 Will do Route Optimization
16 Route Optimization declined, reason unspecified.
5.3. Mobile-Correspondent authentication extension
Mobile-Correspondent authentication extension is included in
registration requests sent from Mobile Router to Correspondent
Router. The existence of this extension indicates that the message
is not destined to a Home Agent, but another Mobile Router. The
format is similar to the other Authentication Extensions defined in
[RFC5944], with SPIs replaced by Nonce Indexes.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Nonce Index | Care-of Nonce Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authenticator... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Home Nonce Index field tells the Correspondent Router which nonce
value to use when producing the home keygen token. The Care-of Nonce
Index field is ignored in requests to remove a binding. Otherwise,
it tells the Correspondent Router which nonce value to use when
producing the Care-of Keygen Token.
Type TBA_T2 (non-skippable). "Short" extension format.
Sub-Type 2
Reserved Set to zero, MUST be ignored on reception.
Home Nonce Index
Home Nonce Index in use.
Care-of Nonce Index
Care-of Index in use.
Authenticator
Authenticator field, by default constructed with First(128,
HMAC_SHA1 (KRm, Protected Data))
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The protected data, just like on other cases where Authenticator is
used, consists of
o the UDP payload (i.e., the Registration Request or Registration
Reply data),
o all prior Extensions in their entirety, and
o the Type, Length, and Nonce Indexes of this Extension.
5.4. Care-of address Extension
The Care-of Address extension is added to a registration reply sent
by the Correspondent Router to inform the Mobile Router of the
upcoming tunnel endpoint.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1..n Times the following information structure
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Care-of Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type TBA_T2 (Non-skippable), "short" extension format
Length Total length of the packet. When processing the
information structures, if Length octets have been reached,
this is an indication that the final information structure
was reached as well.
Sub-Type 3
Care-of Address
Care-of address(es) which may be used for tunnel with
Mobile Router, in order of priority. Multiple CoA's MAY be
listed to facilitate faster NAT traversal.
5.5. Route optimization prefix advertisement
This non-skippable extension MAY be sent by a Home Agent to a Mobile
Router in the registration reply message. The extension is only
included when explicitly requested by the Mobile Router in the
registration request message, setting 'R'-flag of the Mobile Router
Route Optimization capability extension. Implicit prioritization of
prefixes is caused by the order of extensions.
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The extension contains a sequence of information structures. An
information structure may consist of either an MR HoA or a network
prefix. Any network prefixes following an MR HoA are owned by that
MR. An MR HoA MUST be first in sequence, since you cannot have
prefixes without an MR.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Sub-type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1..n times the following information structure
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|M| Plen/Info | Optional Mobile Router HoA, 4 octets ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Optional Prefix, 1,2,3 or 4 octets ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Realm (1..n characters) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type TBA_T3 (Non-skippable), "long" extension format
Sub-Type 1
Length Total length of the packet. When processing the
information structures, if Length octets have been reached,
this is an indication that the final information structure
was reached as well.
D Delta. If D=1, the prefix is a delta from last Prefix
where D=0. MUST be zero on first information structure,
MAY be zero or one on subsequent information structures.
If D=1, the Prefix field is one octet in length. See
Section 4.1 for details.
M Mobile Router HoA bit. If M=1, the next field is Mobile
Router HoA, and Prefix and Realm are omitted. If M=0, the
next field is Prefix followed by Realm, and Mobile Router
HoA is omitted. For the first information structure, M
MUST be set to 1. If M=1, the D bit is set to zero and
ignored upon reception.
PLen/Info This field is interpreted differently depending on whether
M is set or not. If M=0, this indicates the length of the
prefix advertised. 6 bits, allows for values from 0 to 63,
of which 33-63 are illegal. If M=1, the Information field
can be set to zero to indicate no specific information, or
to 1 to indicate "outbound connections only". This
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indicates that the target Mobile Router can only initiate,
not receive, connections on any of it's interfaces (apart
from the reverse tunnel to HA). This is set if the Mobile
Router has explicitly requested it by the 'O' flag in
Mobile router Route optimization capability extension
(Section 5.1).
Mobile router HoA
Mobile Router's Home address. All prefixes in the
following information structures where M=0 are maintained
by this Mobile Router. This field is present only when M =
1.
Prefix The IPv4 prefix advertised. If D=0, the field length is
Plen bits, rounded up to nearest full octet. Least-
significant bits starting off Plen (and are zeros) are
omitted. If D=1, field length is one octet. This field is
present only when M = 0.
Realm The Realm that is associated with the advertised Mobile
Router HoA and prefix. If empty, MUST be set to '\0'. For
realm encoding and optional compression scheme, refer to
Section 4.2. This field is present only when M = 0.
5.6. Home-Test Init message
This message is sent from Mobile Router to Correspondent Router when
performing Return Routability procedure. The source and destination
IP addresses are set to MR's Home Address and CR's Home Address,
respectively. The UDP source port MAY be randomly chosen. The UDP
destination port is 434.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Home Init Cookie |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type TBA_MIP1
Reserved Set to zero, MUST be ignored on reception.
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Home Init Cookie
64-bit field which contains a random value, the Home Init
Cookie.
5.7. Care-of-Test Init message
This message is sent from Mobile Router to Correspondent Router when
performing Return Routability procedure. The source and destination
IP addresses are set to MR's Care-of-Address and CR's Home Address,
respectively. The UDP source port MAY be randomly chosen. The UDP
destination port is 434.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Care-of Init Cookie |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type TBA_MIP2
Reserved Set to zero, MUST be ignored on reception.
Care-of Init Cookie
64-bit field which contains a random value, the Care-of
Init Cookie.
5.8. Home Test message
This message is sent from Correspondent Router to Mobile Router when
performing Return Routability procedure as a reply to Home-Test Init
message. The source and destination IP addresses, as well as UDP
ports, are reversed from the Home-Test Init message the message is
constructed for. As such, the UDP source port is always 434.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | Nonce Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Home Init Cookie +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Home Keygen Token +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type TBA_MIP3
Reserved Set to zero, MUST be ignored on reception.
Nonce Index
This field will be echoed back by the Mobile Router to the
Correspondent Router in a subsequent registration request's
authentication extension.
Home Init Cookie
64-bit field which contains a random value, the Home Init
Cookie.
Home Keygen Token
This field contains the 64 bit home keygen token used in
the Return Routability procedure. Generated from cookie +
nonce.
5.9. Care-of test message
This message is sent from Correspondent Router to Mobile Router when
performing Return Routability procedure as a reply to Care-of-test
Init message. The source and destination IP addresses, as well as
UDP ports, are reversed from the Care-of-test Init message the
message is constructed for. As such, the UDP source port is always
434.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | Nonce Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Care-of Init Cookie +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Care-of Keygen Token +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type TBA_MIP4
Reserved Set to zero, MUST be ignored on reception.
Care-of Nonce Index
This field will be echoed back by the Mobile Router to the
Correspondent Router in a subsequent registration requests'
authentication extension.
Care-of Init Cookie
64-bit field which contains a random value, the Home Init
Cookie.
Care-of Keygen Token
This field contains the 64 bit home keygen token used in
the Return Routability procedure. Generated from cookie +
nonce.
6. Special Considerations
6.1. NATs and stateful firewalls
Mechanisms described in MIP NAT traversal [RFC3519] allow the Home
Agent to work with Mobile Routers situated behind a NAT device or a
stateful firewall. Furthermore, the Home Agent may also detect
whether NAT device is located between the Mobile Node and the HA.
Mobile Router may also explicitly state it is behind a NAT or
firewall on all interfaces, and this information is passed on to the
other Mobile Routers with the information field in Route optimization
prefix advertisement extension (Section 5.5). Home Agent may also
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detect presence of NAT and informs the registering Mobile Router with
the 'N' flag in Route Optimization Reply extension (Section 5.2). In
the case of one or both of the routers is known to be behind NAT or
similarly impaired (not being able to accept incoming connections),
the tunnel establishment procedure needs to take this into account.
In the case where Mobile Router is behind NAT (or firewall) and
Correspondent Router is not, the Mobile Router will, when tunnel has
been established, send keepalive messages (ICMP echo requests)
through the tunnel. Until a reply has been received, the tunnel
SHOULD NOT be considered active. Once reply has been received, NAT
mapping is in place and traffic can be sent.
Source address may change due to NAT in CoTI and Registration Request
messages. This does not affect the process - the hash values are
calculated by the translated address, and the Registration Request
will also appear from the same translated address.
Unlike in communication with the Home Agent, in the case of Route
Optimization the path used for signaling is not used for tunneled
packets, as signaling always uses Home Addresses, and MR <-> CR
tunnel is from CoA to CoA. It is assumed that even though port
numbers may change, NAT processing rarely allocates more than one
external IP address to a single internal address, thus the IP address
seen in the Registration Request and Tunnel packets remains the same.
However, the UDP source port number may be different in Registration
Request and incoming tunnel packets due to port translation. This
must not cause an error situation - the Correspondent Router MUST be
able to accept tunneling packets from a different UDP source port
than what was used in the Registration Request.
Since Mobile Routers may have multiple interfaces connecting to
several different networks, it might be possible that specific Mobile
Routers may only be able to perform Route Optimization using specific
Care-of-address pairs, obtained from specific networks, for example
in a case where two Mobile Routers have an interface behind same NAT.
Similar case may be applicable to nested NATs. In such cases, Mobile
Router MAY attempt to detect eligible Care-of-Address pairs by
performing a registration and attempting to establish a tunnel
(sending keepalives) with each Care-of-Address listed in the
Registration Reply's Care-of-Address extension. The eligible pairs
should be recorded in Route Optimization cache. If tunnel cannot be
established with any CoA's, the Mobile Router MAY attempt to repeat
the procedure with alternative interfaces. The above information on
network topology can also be configured to the Mobile Routers either
statically or via some external feedback mechanism.
If both the Mobile Router and the Correspondent Router are behind two
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separate NATs, some sort of proxy or hole-punching technique may be
applicable. This is out of scope of this document.
6.2. Handling of concurrent handovers
If both Mobile Router and Correspondent Router move at the same time,
this causes no issues from signaling perspective, as all requests are
always sent from a Care-of-Address to Home Addresses. Thus, the
recipient will always receive the request and can send the reply.
This applies even in break-before-make situations where both MR and
CR get disconnected at same time - once the connectivity is restored,
one end-point of the signaling messages is always the Home Address of
respective router, and it is up to the Home Agent to provide
reachability.
6.3. Foreign Agents
Since Foreign Agents have been dropped from Network Mobility for
Mobile IPv4 work, they are not considered here.
6.4. Multiple Home Agents
Mobile Routers can negotiate and perform route optimization without
the assistance of Home Agent - if they can discover each others
existence and thus know where to send registration messages. This
document only addresses a logically single Home Agent that
distributes network prefix information to the Mobile Routers.
Problems arise from possible trust relationships; In this document
the Home Agent serves as a way to provide verification that a
specific network is managed by a specific router.
If Route Optimization is desired between nodes attached to separate
Home Agents, there are several possibilities. Note that standard
high availability redundancy protocols, such as VRRP, can be
utilized; However, in such case the Home Agent is still a single
logical entity even if consisting of more than a single node.
Several possibilities exist for achieving Route Optimization between
Mobile Routers attached to separate Home Agents, such as a new
discovery/probing protocol, routing protocol between Home Agents or
DNS SRV records, or a common AAA architecture. There already is a
framework for HA to retrieve information from AAA so it can be
considered as the most viable possibility. See Section 6.6 for
information on possibility to generalize the method.
Any discovery/probing protocols are out of scope for this document.
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6.5. Mutualness of Route Optimization
The procedure as specified is asymmetric; That is, if bidirectional
route optimization is desired while maintaining consistency, the
route optimization (RR check and registration) has to be performed in
both directions, but this is not strictly necessary. This is
primarily a policy decision depending on how often the mobile
prefixes are reconfigured.
Consider the case where two networks, A and B, are handled by Mobile
Routers A and B respectively. If the routers are set up in such a
fashion that Route Optimization is triggered when a packet is
received from a Network Prefix in Route Optimization Cache, the
following occurs if a node in network A starts sending ICMP echo
requests (pinging) a node in network B.
MR B sees the incoming ICMP echo request packet, which is travelling
inside the reverse tunnel to the Home Agent. MR B sees that the
destination is in network B, and furthermore, source is in network A
which exists in the cache. This triggers Route Optimization
processing. Until RO is active, the ping packets (echo requests and
replies) are routed via the reverse tunnel.
MR B completes RR procedure and registration with MR A, which thus
becomes a Correspondent Router for MR B. A tunnel is created between
the routers. MR A updates its routing tables so that network B is
reachable via MR A <-> MR B tunnel.
The traffic pattern is now that packets from network B to network A
are sent over the direct tunnel, but the packets from A to B are
transmitted via the Home Agent and reverse tunnels. MR A now
performs its own registration towards MR B. Upon completion, MR A
notices that a tunnel to MR B already exists, but updates its routing
table so that network B is now reachable via the MR A <-> MR B
tunnel. From this point onward, traffic is bidirectional.
In this scenario, if MR A does NOT perform a separate route
optimization (RR check and registration), but instead simply updates
its routing table to reach network B via the tunnel, problems may
arise if MR B has started to manage another network B' before the
information has propagated to MR A. The end result is that MR B
starts to receive packets for network B' via the Home Agent and for
network B via direct tunnel. If Reverse Path checking or similar
mechanism is in use on MR B, packets from network A could be black
holed.
Whether to perform this mutual registration or not thus depends on
the situation, and whether Mobile Routers are going to start managing
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additional Network Prefixes during operation.
6.6. Extensibility
The design considerations include several mechanisms which might not
be strictly necessary if Route Optimization would only be desired
between individual customer sites in a managed network. The
registration procedure (with the optional Return Routability part),
which allows for Correspondent Routers to learn Mobile Router's
Care-of Addresses is not strictly necessary; The CoA's could have
been provided by HA directly.
However, this approach allows the method to be extended to a more
generic route optimization. The primary driver for having Home Agent
to work as a centralized information distributer is to provide Mobile
Routers with the knowledge of not only the other routers, but to
provide information on which networks are managed by which routers.
The Home Agent provides the information on all feasible nodes with
which it is possible to establish Route Optimization. If
representing a whole Mobile Network is not necessary, in effect the
typical Mobile Node <-> Correspondent Node situation, the mechanisms
in this document work just as well - only problem is discovering if
the target Correspondent Node can provide Route Optimization
capability. This can be performed by not including any prefixes in
the information extension, just the HoA address of Mobile Router.
In addition, with Route Optimization for single node, checks on
whether a Mobile Router is allowed to represent specific networks are
unnecessary since there are none.
Correspondent node/router discovery protocols (whether they are based
on probing or a centralized directory beyond the single Home Agent)
are outside the scope of this document.
6.7. Load Balancing
The design simply provides possibility to create optimal paths
between Mobile Routers; It doesn't dictate what should be the user
traffic using these paths. One possible approach in helping
facilitate load balancing and utilizing all available paths is
presented in [I-D.ietf-mip4-multiple-tunnel-support], which
effectively allows for multiple Care-of addresses for a single Home
Address. In addition, per-tunnel load balancing is possible by using
separate Care-of-Addresses for separate tunnels.
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7. Scalability
Home Agent assisted Route Optimization scalability issues stem from
the general Mobile IPv4 architecture which is based on tunnels.
Creating, maintaining and destroying tunnel interfaces can cause load
on the Mobile Routers. However, the MRs can always fall back to
normal, reverse tunnelled routing if resource constraints are
apparent.
If there is a large number of optimization-capable prefixes,
maintaining state for all of these may be an issue also, due to
limits on routing table sizes.
Registration responses from Home Agent to Mobile Router may provide
information on large number of network prefixes. If thousands of
networks are involved, the registration reply messages are bound to
grow very large. The prefix- and realm compression mechanisms
defined in Section 4 mitigates this problem to an extent. There
will, however, be some practical upper limit after which point some
other delivery mechanism for the prefix information will be needed.
8. Example signaling scenarios
8.1. Registration request
The following example signaling assumes that there are three Mobile
Routers, MR A, B, C, each managing network prefixes A, B, and C. At
the beginning, no networks are registered to the Home Agent. Any AAA
processing at the Home Agent is omitted from the diagram.
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+--------+ +--------+ +--------+ +--------------+
| [MR A] | | [MR B] | | [MR C] | | [Home Agent] |
+--------+ +--------+ +--------+ +--------------+
| | | |
x------------------------------->| Registration request,
| | | | includes Mobile Router
| | | | route optimization
| | | | capability extension
| | | |
|<-------------------------------x Registration response,
| | | | no known networks from HA
| | | | in response
| | | |
| x-------------------->| Registration request, similar
| | | | to the one sent by MR A
| | | |
| |<--------------------x Registration reply, includes
| | | | network A in route optimization
| | | | prefix advertisement extension
| | | |
| | x--------->| Registration request, similar
| | | | the one sent by MR A
| | | |
| | |<---------x Registration reply, includes
| | | | networks A and B in route
| | | | optimization prefix
| | | | advertisement extension.
| | | | Network B is sent in
| | | | compressed form.
| | | |
8.2. Route optimization with return routability
The following example signaling has same network setup as in
Section 8.1 - Three mobile routers, each corresponding to their
respective network. Node A is in network A and Node C is in network
C.
At the beginning, no mobile routers know KRm's of each other. If the
KRm's would be pre-shared or provisioned with some other method, the
Return Routability messages can be omitted. Signaling in Section 8.1
has occurred, thus MR A is not aware of the other networks, and MR C
is aware of networks A and B.
======= Traffic inside Mobile IP tunnel to/from HA
=-=-=-= Traffic inside Mobile IP tunnel between MRs
------- Traffic outside Mobile IP tunnel
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+----------+ +--------+ +------+ +--------+ +----------+
| [Node A] | | [MR A] | | [HA] | | [MR C] | | [Node C] |
+----------+ +--------+ +------+ +--------+ +----------+
| | | | |
x------------O==========O=========O------>| Mobile Router A is
| | | | | unaware of network C,
| | | | | thus, nothing happens
| | | | |
|<-----------O==========O=========O-------x Mobile Router C
| | | | | notices packet to
| | | | | Net A - begins RO
| | | | |
| | | | | Return Routability
| | | | | (If no preshared KRms)
| | | | |
| |<=========O---------x | CoTI
| |<=========O=========x | HoTI
| | | | |
| x==========O-------->| | CoT
| x==========O========>| | HoT
| | | | |
| | | | | KRm between MR A <-> C
| | | | | established
| | | | |
| |<=========O---------x | Registration request
| | | | |
| x--------->| | | Registration request
| | | | | to HA due to MR A
| | | | | being unaware of
| | | | | network C.
| | | | | Solicit bit set.
| | | | |
| |<---------x | | Registration reply,
| | | | | contains info on Net A
| | | | |
| x==========O-------->| | Registration reply,
| | | | | includes MR A's CoA in
| | | | | Care-of-Address
| | | | | extension
| | | | |
| |<= = = = =O= = = ==>| | Optional mutual registration
| | | | | from MR A to MR C (same
| | | | | procedure as above,
| | | | | multiple packets),
| | | | | possible keepalive checks
| | | | |
|<-----------O=-=-=-==-=-=-=-==-=-O-------x Packet from Node C -> A
| | | | | routed to direct tunnel
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| | | | | at MR C, based on
| | | | | MR C now knowing MR A's
| | | | | CoA and tunnel being up
| | | | |
x------------O=-=-=-==-=-=-=-==-=-O------>| Packet from Node A -> C
| | | | | routed to direct tunnel
| | | | | at MR A, based on MR A
| | | | | now knowing MR C's CoA
| | | | | and tunnel being up
8.3. Handovers
In this example signaling, MR C changes care-of address while Route
Optimization between MR A is operating and data is being transferred.
Both cases where the handover is graceful ("make before break") and
ungraceful ("break before make") occur in similar fashion, except in
the graceful version no packets get lost. This diagram considers the
case where MR C gets immediate notification of lost connectivity e.g.
due to link status indication. MR A would eventually notice the
breakdown due to keepalive messages failing.
======= Traffic inside Mobile IP tunnel to/from HA
=-=-=-= Traffic inside Mobile IP tunnel between MRs
------- Traffic outside Mobile IP tunnel
+----------+ +--------+ +------+ +--------+ +----------+
| [Node A] | | [MR A] | | [HA] | | [MR C] | | [Node C] |
+----------+ +--------+ +------+ +--------+ +----------+
| | | | |
x------------O=-=-=-==-=-=-=-==-=-O------>| Nodes A and C
|<-----------O=-=-=-==-=-=-=-==-=-O-------x exchanging traffic
| | | | |
| | xxxxxxxxxxx | Break occurs: MR C
| | | | | loses connectivity to
| | | | | current attachment point
| | | | |
x------------O=-=-=-==-=-=-=->x | | Traffic from A -> C
| | | | | lost and
| | | x<=-=-O-------x vice versa
| | | | |
| | |<--------x | MR C finds a new
| | | | | point of attachment,
| | | | | registers to HA, clears
| | | | | routing tables
| | | | |
| | x-------->| | Registration reply
| | | | |
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x------------O=-=-=-==-=-=-=->x | | Traffic from A -> C
| | | | | lost (reverts to routing
| | | | | via HA if enough keepalives
| | | | | fail)
| | | | |
|<-----------O==========O=========O-------| Traffic from C -> A
| | | | | sent via HA
| | | | |
| O<=========O---------x | CoTI message
| | | | | (partial RR check)
| | | | |
| x==========O-------->| | CoT message
| | | | |
| |<=========O---------x | Registration request,
| | | | | reusing newly calculated KRm
| | | | |
| x==========O-------->| | Registration reply
| | | | |
| O<=-=-=-=-=-=-=-=-=-=x | First keepalive check if using
| | | | | UDP encapsulation, also
| x=-=-=-=-=-=-=-=-=-=>| | creates holes in firewalls
| | | | |
| | | | |
x------------O=-=-=-==-=-=-=-==-=-O------>| Traffic from A -> C
| | | | | forwarded directly again
| | | | |
|<-----------O=-=-=-==-=-=-=-==-=-O-------x Traffic from C -> A
| | | | | switches back to direct
| | | | | tunnel
| | | | |
9. Protocol constants
MAX_NONCE_LIFETIME 240 seconds
MAX_TOKEN_LIFETIME 210 seconds
MAX_UPDATE_RATE 5 times
10. IANA Considerations
IANA has assigned rules for the existing registries "Mobile IP
Message Types" and "Extensions to Mobile IP Registration Messages",
specified in RFC 5944 [RFC5944]. New Mobile IP message types and
extension code allocations are needed for the messages and extensions
listed in section 5.
The Route Optimization authentication processing requires four new
message type numbers. The new Mobile IP Message types are listed
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below, in Table 1. They should preferably be allocated from a
contiguous range.
+----------+---------------------------+
| Value | Name |
+----------+---------------------------+
| TBA_MIP1 | Home-Test Init message |
| TBA_MIP2 | Care-of-Test Init message |
| TBA_MIP3 | Home Test message |
| TBA_MIP4 | Care-of Test message |
+----------+---------------------------+
Table 1: New Values for Mobile IP Message types
Three new registration message extension types are required and
listed in Table 2. The first type, TBA_T1 is skippable and should be
allocated from range 128-255. The other two, TBA_T2 and TBA_T3 are
non-skippable and should be allocated from range 0-127, TBA_T2 being
of the "short" format and TBA_T3 being of the "long" format. None of
the messages are permitted for notification messages.
+-----------------+---------------------------------------------+
| Value | Name |
+-----------------+---------------------------------------------+
| TBA_T1, 128-255 | Mobile router Route optimization indication |
| TBA_T2, 0-127 | Route Optimization Extensions |
| TBA_T3, 0-127 | Route Optimization data |
+-----------------+---------------------------------------------+
Table 2: New Values and Names for Extensions in Mobile IP
Registration messages
In addition, the registry "Code Values for Mobile IP Registration
Reply Messages" needs to be modified. A new success code, TBA_S1,
should be allocated as follows:
TBA_S1 Concurrent registration (pre-accept)
In addition, a new allocation range needs to be created as "Error
Codes from the Correspondent Node", subject to policy of Expert
Review [RFC5226]. Suggested range is 201-210. Three new
registration reply codes are to be allocated from this range. They
are specified in Table 3, below:
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+--------+-----------------------------+
| Value | Name |
+--------+-----------------------------+
| TBA_C1 | Expired Home nonce Index |
| TBA_C2 | Expired Care-of nonce Index |
| TBA_C3 | Expired nonces |
+--------+-----------------------------+
Table 3: New Values for Code Values for Mobile IP Registration Reply
Messages
Three new number spaces are required for the subtypes of the
extensions in Table 2. A new registry, named "Route Optimization
Types and Subtypes" is created with an allocation policy of RFC
Required [RFC5226]. The registration entries include Type, Subtype
and Name. Type and Subtype have range of 0-255. Types are
references to registration message extension types. Subtypes are
allocated initially as in Table 4, below:
+--------+---------+-----------------------------------------------+
| Type | Subtype | Name |
+--------+---------+-----------------------------------------------+
| TBA_T1 | 0 | Reserved |
| TBA_T1 | 1 | Mobile router Route optimization capability |
| TBA_T2 | 0 | Reserved |
| TBA_T2 | 1 | Route optimization reply |
| TBA_T2 | 2 | Mobile-Correspondent authentication extension |
| TBA_T2 | 3 | Care-of address extension |
| TBA_T3 | 0 | Reserved |
| TBA_T3 | 1 | Route optimization prefix advertisement |
+--------+---------+-----------------------------------------------+
Table 4: Initial Values and Names for registry Route Optimization
Types and Subtypes
11. Security Considerations
There are two primary security issues: Other relates to return
routability check, which establishes that a specific Care-of address
is, indeed, managed by a specific Home Address. Other issue is trust
relationships and arbitrary router claiming to represent arbitrary
network.
The end-user traffic can be protected using normal IPSec mechanisms.
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11.1. Return Routability
The Return Routability check's security has been vetted with Mobile
IPv6. There are no large differences apart from requiring a separate
ICMP message for connectivity check, and replay attack protection,
which in this case uses Mobile IPv4 timestamps in registration
request's identification field instead of sequence numbers.
The Return Routability procedure does not establish any kind of state
information on the Correspondent router, mitigating Denial of Service
attacks. State information is only maintained after a Registration
request has been accepted.
11.2. Trust relationships
The network of trust relationships in Home Agent assisted Route
Optimization solve the issues where arbitrary Correspondent Router
can trust an arbitrary Mobile Router that it is indeed the proper
route to reach an arbitrary mobile network.
It is assumed that all Mobile Routers have a trust relationship with
the Home Agent. Thus, they trust information provided by Home Agent.
The Home Agent provides information matching Home Addresses and
network prefixes. Each Mobile Router trusts this information.
Mobile Routers may perform Return Routability procedure between each
other. This creates a trusted association between Mobile Router Home
Address and Care-of Address. The Mobile Router also claims to
represent a specific network. This information is not trustworthy as
such.
The claim can be verified by checking the Home Address <-> network
prefix information received, either earlier, or due to on-demand
request, from the Home Agent. If they match, the Mobile Router's
claim is authentic. If the network is considered trusted, a policy
decision can be made to skip this check. Exact definitions on
situations where such decision can be made are out of scope of this
document. The RECOMMENDED general practice is to perform the check.
12. Acknowledgements
Thanks to Alexandru Petrescu for constructive comments and support.
Thanks to Jyrki Soini and Kari Laihonen for initial reviews.This work
was supported by TEKES as part of the Future Internet program of
TIVIT (Finnish Strategic Centre for Science, Technology and
Innovation in the field of ICT).
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13. References
13.1. Normative References
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC3519] Levkowetz, H. and S. Vaarala, "Mobile IP Traversal of
Network Address Translation (NAT) Devices", RFC 3519,
April 2003.
[RFC5177] Leung, K., Dommety, G., Narayanan, V., and A. Petrescu,
"Network Mobility (NEMO) Extensions for Mobile IPv4",
RFC 5177, April 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5944] Perkins, C., "IP Mobility Support for IPv4, Revised",
RFC 5944, November 2010.
13.2. Informative References
[I-D.ietf-mip4-multiple-tunnel-support]
Gundavelli, S., Leung, K., Tsirtsis, G., Soliman, H., and
A. Petrescu, "Flow Binding Support for Mobile IPv4",
draft-ietf-mip4-multiple-tunnel-support-02 (work in
progress), August 2011.
[I-D.ietf-mobileip-optim]
Perkins, C. and D. Johnson, "Route Optimization in Mobile
IP", September 2001.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC3543] Glass, S. and M. Chandra, "Registration Revocation in
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Mobile IPv4", RFC 3543, August 2003.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", RFC 4282, December 2005.
Authors' Addresses
Antti Makela
Aalto University, Department of Communications and Networking (Comnet)
P.O. BOX 13000
FIN-00076 Aalto
FINLAND
Email: antti.makela@aalto.fi
Jouni Korhonen
Nokia Siemens Networks
Linnoitustie 6
FI-02600 Espoo
FINLAND
Email: jouni.nospam@gmail.com
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