Internet DRAFT - draft-ietf-softwire-map-t
draft-ietf-softwire-map-t
Softwires Working Group X. Li
Internet-Draft C. Bao
Intended status: Standards Track CERNET Center/Tsinghua University
Expires: June 5, 2015 W. Dec, Ed.
O. Troan
Cisco Systems
S. Matsushima
SoftBank Telecom
T. Murakami
IP Infusion
December 2, 2014
Mapping of Address and Port using Translation (MAP-T)
draft-ietf-softwire-map-t-08
Abstract
This document specifies the "Mapping of Address and Port" stateless
IPv6-IPv4 Network Address Translation (NAT64) based solution
architecture for providing shared or non-shared IPv4 address
connectivity to and across an IPv6 network.
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
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This Internet-Draft will expire on June 5, 2015.
Copyright Notice
Copyright (c) 2014 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Mapping Rules . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Destinations outside the MAP domain . . . . . . . . . . . 7
6. The IPv6 Interface Identifier . . . . . . . . . . . . . . . . 7
7. MAP-T Configuration . . . . . . . . . . . . . . . . . . . . . 8
7.1. MAP CE . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.2. MAP BR . . . . . . . . . . . . . . . . . . . . . . . . . 9
8. MAP-T Packet Forwarding . . . . . . . . . . . . . . . . . . . 9
8.1. IPv4 to IPv6 at the CE . . . . . . . . . . . . . . . . . 9
8.2. IPv6 to IPv4 at the CE . . . . . . . . . . . . . . . . . 10
8.3. IPv6 to IPv4 at the BR . . . . . . . . . . . . . . . . . 11
8.4. IPv4 to IPv6 at the BR . . . . . . . . . . . . . . . . . 11
9. ICMP Handling . . . . . . . . . . . . . . . . . . . . . . . . 11
10. Fragmentation and Path MTU Discovery . . . . . . . . . . . . 12
10.1. Fragmentation in the MAP domain . . . . . . . . . . . . 12
10.2. Receiving IPv4 Fragments on the MAP domain borders . . . 12
10.3. Sending IPv4 fragments to the outside . . . . . . . . . 13
11. NAT44 Considerations . . . . . . . . . . . . . . . . . . . . 13
12. Usage Considerations . . . . . . . . . . . . . . . . . . . . 13
12.1. EA-bit length 0 . . . . . . . . . . . . . . . . . . . . 13
12.2. Mesh and Hub and spoke modes . . . . . . . . . . . . . . 13
12.3. Communication with IPv6 servers in the MAP-T domain . . 14
12.4. Compatibility with other NAT64 solutions . . . . . . . . 14
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
14. Security Considerations . . . . . . . . . . . . . . . . . . . 14
15. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
17.1. Normative References . . . . . . . . . . . . . . . . . . 16
17.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Examples of MAP-T translation . . . . . . . . . . . 19
Appendix B. Port mapping algorithm . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
Experiences from initial service provider IPv6 network deployments,
such as [RFC6219], indicate that successful transition to IPv6 can
happen while supporting legacy IPv4 users without a full end-to-end
dual IP stack deployment. However, due to public IPv4 address
exhaustion this requires an IPv6 technology that supports IPv4 users
utilizing shared IPv4 addressing, while also allowing the network
operator to optimize their operations around IPv6 network practices.
The use of double NAT64 translation based solutions is an optimal way
to address these requirements, especially in combination with
stateless translation techniques that minimize operational challenges
outlined in [I-D.ietf-softwire-stateless-4v6-motivation].
The Mapping of Address and Port - Translation (MAP-T) architecture
specified in this draft is such a double stateless NAT64 based
solution. It builds on existing stateless NAT64 techniques specified
in [RFC6145], along with the stateless algorithmic address &
transport layer port mapping scheme defined in MAP-E
[I-D.ietf-softwire-map]. The MAP-T solution differs from MAP-E in
the use of IPv4-IPv6 translation, rather than encapsulation, as the
form of IPv6 domain transport. The translation mode is considered
advantageous in scenarios where the encapsulation overhead, or IPv6
operational practices (e.g. Use of IPv6 only servers, or reliance on
IPv6 + protocol headers for traffic classification) rule out
encapsulation. These scenarios are presented in
[I-D.maglione-softwire-map-t-scenarios]
2. Conventions
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].
3. Terminology
MAP-T Mapping of Address and Port by means of
address Translation.
MAP Customer Edge (CE): A device functioning as a Customer Edge (CE)
router in a MAP deployment. A typical MAP CE
adopting MAP rules will serve a residential
site with one WAN side IPv6 addressed
interface, and one or more LAN side
interfaces addressed using private IPv4
addressing.
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MAP Border Relay (BR): A MAP enabled router managed by the service
provider at the edge of a MAP domain. A
Border Relay (BR) router has at least an
IPv6-enabled interface and an IPv4 interface
connected to the native IPv4 network. A MAP
BR may also be referred to simply as a "BR"
within the context of MAP.
MAP domain: One or more MAP CEs and BRs connected by
means of an IPv6 network and sharing a common
set of MAP Rules. A service provider may
deploy a single MAP domain, or may utilize
multiple MAP domains.
MAP Rule: A set of parameters describing the mapping
between an IPv4 prefix, IPv4 address or
shared IPv4 address and an IPv6 prefix or
address. Each MAP domain uses a different
mapping rule set.
MAP Rule set: A Rule set is composed out of all the MAP
Rules communicated to a device, that are
intended for determining the devices' IP+port
mapping and forwarding operations. The MAP
Rule set is interchangeably referred to in
this document as a MAP Rule table or simply
Rule table. Two specific types of rules,
Basic Mapping Rule (BMR) and Forward Mapping
Rule (FMR), are defined in Section 5 of
[I-D.ietf-softwire-map]. The Default Mapping
Rule (DMR) is defined in this document.
MAP Rule table: See MAP Rule set.
MAP node: A device that implements MAP.
Port-set: Each node has a separate part of the
transport layer port space; denoted as a
port-set.
Port-set ID (PSID): Algorithmically identifies a set of ports
exclusively assigned to the CE.
Shared IPv4 address: An IPv4 address that is shared among multiple
CEs. Only ports that belong to the assigned
port-set can be used for communication. Also
known as a Port-Restricted IPv4 address.
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End-user IPv6 prefix: The IPv6 prefix assigned to an End-user CE by
other means than MAP itself. E.g.
Provisioned using DHCPv6 PD [RFC3633],
assigned via SLAAC [RFC4862], or configured
manually. It is unique for each CE.
MAP IPv6 address: The IPv6 address used to reach the MAP
function of a CE from other CEs and from BRs.
Rule IPv6 prefix: An IPv6 prefix assigned by a Service Provider
for a MAP rule.
Rule IPv4 prefix: An IPv4 prefix assigned by a Service Provider
for a MAP rule.
Embedded Address (EA) bits: The IPv4 EA-bits in the IPv6 address
identify an IPv4 prefix/address (or part
thereof) or a shared IPv4 address (or part
thereof) and a port-set identifier.
4. Architecture
Figure 1 depicts the overall MAP-T architecture, which sees any
number of privately addressed IPv4 users (N and M) connected by means
of MAP-T CEs to an IPv6 network that is equipped with one or more
MAP-T BR. CEs and BRs that share MAP configuration parameters,
referred to as MAP rules, form a MAP-T Domain.
Functionally the MAP-T CE and BR utilize and extend some well
established technology building blocks to allow the IPv4 users to
correspond with nodes on the Public IPv4 network, or IPv6 network as
follows:
o A (NAT44) NAPT [RFC2663] function on a MAP CE is extended with
support for restricting the allowable TCP/UDP ports for a given
IPv4 address. The IPv4 address and port range used are determined
by the MAP provisioning process and identical to MAP-E
[I-D.ietf-softwire-map].
o A stateless NAT64 function [RFC6145] is extended to allow
stateless mapping of IPv4 and transport layer port ranges to IPv6
address space.
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User N
Private IPv4
| Network
|
O--+---------------O
| | MAP-T CE |
| +-----+--------+ |
| NAPT44| MAP-T | |
| +-----+ | +-._ ,-------. .------.
| +--------+ | ,-' `-. ,-' `-.
O------------------O / \ O---------O / Public \
/ IPv6 only \ | MAP-T |/ IPv4 \
( Network --+ Border +- Network )
\ / | Relay |\ /
O------------------O \ / O---------O \ /
| MAP-T CE | ;". ,-' `-. ,-'
| +-----+--------+ | ," `----+--' ------'
| NAPT44| MAP-T | |, |
| +-----+ | + IPv6 node(s)
| | +--------+ | (w/ v4-embedded-v6 address)
O---+--------------O
|
User M
Private IPv4
Network
Figure 1: MAP-T Architecture
Each MAP-T CE is assigned with a regular IPv6 prefix from the
operator's IPv6 network. This, in conjunction with MAP domain
configuration settings and the use of the MAP procedures allows the
computation of a MAP IPv6 address and a corresponding IPv4 address.
To allow for IPv4 address sharing, the CE may also have be configured
with a TCP/UDP port-range that is identified by means of a MAP Port
Set Identifier (PSID) value. Each CE is responsible for forwarding
traffic between a given user's private IPv4 address space and the MAP
domain's IPv6 address space. The IPv4-IPv6 adaptation uses stateless
NAT64, in conjunction with the MAP algorithm for address computation.
The MAP-T BR connects one or more MAP-T domains to external IPv4
networks using stateless NAT64 as extended by the MAP-T behaviour
described in this document.
In contrast to MAP-E, NAT64 technology is used in the architecture
for two purposes. Firstly, it is intended to diminish encapsulation
overhead and allow IPv4 and IPv6 traffic to be treated as similarly
as possible. Secondly, it is intended to allow IPv4-only nodes to
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correspond directly with IPv6 nodes in the MAP-T domain that have
IPv4 embedded IPv6 addresses as per [RFC6052]).
The MAP-T architecture is based on the following key properties i)
algorithmic IPv4-IPv6 address mapping codified as MAP Rules covered
in Section 5 ii) A MAP IPv6 address identifier, described in
Section 6 iii) MAP-T IPv4-IPv6 forwarding behavior described in
Section 8.
5. Mapping Rules
The MAP-T algorithmic mapping rules are identical to those in
Section 5 of the MAP-E specification [I-D.ietf-softwire-map], with
the following exception. The forwarding of traffic to and from IPv4
destinations outside a MAP-T domain is to be performed as described
here under, instead of Section 5.4 of the MAP-E specification.
5.1. Destinations outside the MAP domain
IPv4 traffic sent by MAP nodes that are all within one MAP domain is
translated to IPv6, with the sender's MAP IPv6 address, derived via
the Basic Mapping Rule (BMR), as the IPv6 source address and the
recipient's MAP IPv6 address, derived via the Forward Mapping Rule
(FMR), as the IPv6 destination address.
IPv4 addressed destinations outside of the MAP domain are represented
by means of IPv4-Embedded IPv6 address as per [RFC6052], using the
BR's IPv6 prefix. For a CE sending traffic to any such destination,
the source address of the IPv6 packet will be that of the CE's MAP
IPv6 address, and the destination IPv6 address will be the
destination IPv4-embedded-IPv6 address. This address mapping is
termed as following the MAP-T Default Mapping Rule (DMR) and is
defined in terms of the IPv6 prefix advertised by one or more BRs,
which provide external connectivity. A typical MAP-T CE will install
an IPv4 default route using this rule. A BR will use this rule when
translating all outside IPv4 source addresses to the IPv6 MAP domain.
The DMR IPv6 prefix-length SHOULD be by default 64 bits long, and in
any case MUST NOT exceed 96 bits. The mapping of the IPv4
destination behind the IPv6 prefix will by default follow the /64
rule as per [RFC6052]. Any trailing bits after the IPv4 address are
set to 0x0.
6. The IPv6 Interface Identifier
The Interface identifier format of a MAP-T node is the same as
described in section 6 of [I-D.ietf-softwire-map]. For convenience
this is cited below:
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| 128-n-o-s bits |
| 16 bits| 32 bits | 16 bits|
+--------+----------------+--------+
| 0 | IPv4 address | PSID |
+--------+----------------+--------+
Figure 2
In the case of an IPv4 prefix, the IPv4 address field is right-padded
with zeros up to 32 bits. The PSID is zero left-padded to create a
16 bit field. For an IPv4 prefix or a complete IPv4 address, the
PSID field is zero.
If the End-user IPv6 prefix length is larger than 64, the most
significant parts of the interface identifier is overwritten by the
prefix.
7. MAP-T Configuration
For a given MAP domain, the BR and CE MUST be configured with the
following MAP parameters. The values for these parameters are
identical for all CEs and BRs within a given MAP-T domain.
o The Basic Mapping Rule and optionally the Forwarding Mapping
Rules, including the Rule IPv6 prefix, Rule IPv4 prefix, and
Length of Embedded Address bits
o Use of Hub and spoke mode or Mesh mode. (If all traffic should be
sent to the BR, or if direct CE to CE correspondence should be
supported).
o Use of IPv4-IPv6 Translation (MAP-T)
o The BR's IPv6 prefix used in the DMR
7.1. MAP CE
For a given MAP domain, the MAP configuration parameters are the same
across all CEs within that domain. These values may be conveyed and
configured on the CEs using a variety of methods, including; DHCPv6,
Broadband Forum's "TR-69" Residential Gateway management interface,
Netconf, or manual configuration. This document does not prescribe
any of these methods, but recommends that a MAP CE SHOULD implement
DHCPv6 options as per [I-D.ietf-softwire-map-dhcp]. Other
configuration and management methods may use the data model described
by this option for consistency and convenience of implementation on
CEs that support multiple configuration methods.
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Besides the MAP configuration parameters, a CE requires an IPv6
prefix to be assigned to the CE. This End-user IPv6 prefix is
configured as part of obtaining IPv6 Internet access, and is acquired
using standard IPv6 means applicable in the network where the CE is
located.
The MAP provisioning parameters, and hence the IPv4 service itself,
are tied to the End-user IPv6 prefix; thus, the MAP service is also
tied to this in terms of authorization, accounting, etc.
A single MAP CE MAY be connected to more than one MAP domain, just as
any router may have more than one IPv4-enabled service provider
facing interface and more than one set of associated addresses
assigned by DHCPv6. Each domain a given CE operates within would
require its own set of MAP configuration elements and would generate
its own IPv4 address. Each MAP domain requires a distinct End-user
IPv6 prefix.
7.2. MAP BR
The MAP BR MUST be configured with the same MAP elements as the MAP
CEs operating within the same domain.
For increased reliability and load balancing, the BR IPv6 prefix MAY
be shared across a given MAP domain. As MAP is stateless, any BR may
be used for forwarding to/from the domain at any time.
Since MAP uses provider address space, no specific IPv6 or IPv4
routes need to be advertised externally outside the service
provider's network for MAP to operate. However, the BR prefix needs
to be advertised in the service provider's IGP.
8. MAP-T Packet Forwarding
The end-to-end packet flow in MAP-T involves an IPv4 or IPv6 packet
being forwarded by a CE of BR in one of two directions for each such
case. This section presents a conceptual view of the operations
involved in such forwarding.
8.1. IPv4 to IPv6 at the CE
A MAP-T CE receiving IPv4 packets SHOULD perform NAPT NAT44
processing, and create any necessary NAPT44 bindings. The source
address and source port-range of packets resulting from the NAPT44
processing MUST correspond to the source IPv4 address and source
transport port-range assigned to the CE by means of the MAP Basic
Mapping Rule (BMR).
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The IPv4 packet is subject to a longest IPv4 destination address +
port match MAP rule selection, which then determines the parameters
for the subsequent NAT64 operation. By default, all traffic is
matched to the default mapping rule (DMR), and subject to the
stateless NAT64 operation using the DMR parameters for NAT64
Section 5.1. Packets that are matched to (optional) Forward Mapping
Rules (FMRs) are subject to the stateless NAT64 operation using the
FMR parameters Section 5 for the MAP algorithm. In all cases the
CE's MAP IPv6 address Section 6 is used as a source address.
A MAP-T CE MUST support a Default Mapping Rule and SHOULD support one
or more Forward Mapping Rules.
8.2. IPv6 to IPv4 at the CE
A MAP-T CE receiving an IPv6 packet performs its regular IPv6
operations (filtering, pre-routing, etc). Only packets that are
addressed to the CE's MAP-T IPv6 addresses, and with source addresses
matching the IPv6 map-rule prefixes of a DMR or FMR, are processed by
the MAP-T CE, with the DMR or FMR being selected based on a longest
match. The CE MUST check that each MAP-T received packet's
destination transport-layer destination port number is in the range
allowed for by the CE's MAP BMR configuration. The CE MUST silently
drop any non conforming packet and an appropriate counter
incremented. When receiving a packet whose source IP address longest
matches an FMR prefix, the CE MUST perform a check of consistency of
the source address against the allowed values as per the derived
allocated source port-range. If the source port number of a packet
is found to be outside the allocated range, the CE MUST drop the
packet and SHOULD respond with an ICMPv6 "Destination Unreachable,
Source address failed ingress/egress policy" (Type 1, Code 5).
For each MAP-T processed packet, the CE's NAT64 function MUST compute
an IPv4 source and destination addresses. The IPv4 destination
address is computed by extracting relevant information from the IPv6
destination and the information stored in the BMR as per Section 5.
The IPv4 source address is formed by classifying a packet's source as
longest matching a DMR or FMR rule prefix, and then using the
respective rule parameters for the NAT64 operation.
The resulting IPv4 packet is then forwarded to the CE's NAPT NAPT44
function, where the destination IPv4 address and port number MUST be
mapped to their original value, before being forwarded according to
the CE's regular IPv4 rules. When the NAPT44 function is not
enabled, by virtue of MAP configuration, the traffic from the
stateless NAT64 function is directly forwarded according to the CE's
IPv4 rules.
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8.3. IPv6 to IPv4 at the BR
A MAP-T BR receiving an IPv6 packet MUST select a matching MAP rule
based on a longest address match of the packet's source address
against the MAP Rules present on the BR. In combination with the
Port-Set-Id derived from the packet's source IPv6 address, the
selected MAP rule allows the BR to verify that the CE is using its
allowed address and port range. Thus, the BR MUST perform a
validation of the consistency of the source against the allowed
values from the identified port-range. If the packet's source port
number is found to be outside the range allowed, the BR MUST drop the
packet and increment a counter to indicate the event. The BR SHOULD
also respond with an ICMPv6 "Destination Unreachable, Source address
failed ingress/egress policy" (Type 1, Code 5).
When constructing the IPv4 packet, the BR MUST derive the source and
destination IPv4 addresses as per Section 5 of this document and
translate the IPv6 to IPv4 headers as per [RFC6145]. The resulting
IPv4 packet is then passed to regular IPv4 forwarding.
8.4. IPv4 to IPv6 at the BR
A MAP-T BR receiving IPv4 packets uses a longest match IPv4 +
transport layer port lookup to identify the target MAP-T domain and
select the FMR and DMR rules. The MAP-T BR MUST then compute and
apply the IPv6 destination addresses from the IPv4 destination
address and port as per the selected FMR. The MAP-T BR MUST also
compute and apply the IPv6 source addresses from the IPv4 source
address as per Section 5.1 (i.e. Using the IPv4 source and the BR's
IPv6 prefix it forms an IPv6 embedded IPv4 address). Throughout the
generic IPv4 to IPv6 header translation procedures following
[RFC6145] apply. The resulting IPv6 packets are then passed to
regular IPv6 forwarding.
Note that the operation of a BR when forwarding to/from MAP-T domains
that are defined without IPv4 address sharing is the same as that of
stateless NAT64 IPv4/IPv6 translation.
9. ICMP Handling
MAP-T CEs and BRs MUST follow ICMP/ICMPv6 translation as per
[RFC6145], however additional behavior is also required due to the
presence of NAPT44. Unlike TCP and UDP, which provide two transport
protocol port fields to represent both source and destination, the
ICMP/ICMPv6 [RFC0792], [RFC4443] Query message header has only one ID
field which needs to be used to identify a sending IPv4 host. When
receiving IPv4 ICMP messages, the MAP-T CE MUST rewrite the ID field
to a port value derived from the CE's Port-Set-Id.
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A MAP-T BR receiving an IPv4 ICMP packet , which contains an ID field
that is bound for a shared address in the MAP-T domain, SHOULD use
the ID value as a substitute for the destination port in determining
the IPv6 destination address. In all other cases, the MAP-T BR MUST
derive the destination IPv6 address by simply mapping the destination
IPv4 address without additional port info.
10. Fragmentation and Path MTU Discovery
Due to the different sizes of the IPv4 and IPv6 header, handling the
maximum packet size is relevant for the operation of any system
connecting the two address families. There are three mechanisms to
handle this issue: Path MTU discovery (PMTUD), fragmentation, and
transport-layer negotiation such as the TCP Maximum Segment Size
(MSS) option [RFC0897]. MAP can use all three mechanisms to deal
with different cases.
Note: The NAT64 [RFC6145]mechanism is not lossless. When IPv4
originated communication traverses across a double NAT64 function
(a.k.a. NAT464), any IPv4 originated ICMP-independent PathMTU
Discovery, as specified in [RFC 4821], ceases to be entirely
reliable. This is because the[RFC4821] defined DF=1/MF=1
combination, following a double NAT64 translation, results in DF=0/
MF=1.
10.1. Fragmentation in the MAP domain
Translating an IPv4 packet to carry it across the MAP domain will
increase its size typically by 20 bytes. The MTU in the MAP domain
should be well managed and the IPv6 MTU on the CE WAN side interface
SHOULD be configured so that no fragmentation occurs within the
boundary of the MAP domain.
Fragmentation in MAP-T domain SHOULD be handled as described in
section 4 and 5 of [RFC6145].
10.2. Receiving IPv4 Fragments on the MAP domain borders
Forwarding of an IPv4 packet received from the outside of the MAP
domain requires the IPv4 destination address and the transport
protocol destination port. The transport protocol information is
only available in the first fragment received. As described in
section 5.3.3 of [RFC6346] a MAP node receiving an IPv4 fragmented
packet from outside SHOULD reassemble the packet before sending the
packet onto the MAP domain. If the first packet received contains
the transport protocol information, it is possible to optimize this
behavior by using a cache and forwarding the fragments unchanged. A
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description of such a caching algorithm is outside the scope of this
document.
10.3. Sending IPv4 fragments to the outside
Two IPv4 hosts behind two different MAP CE's with the same IPv4
address sending fragments to an IPv4 destination host outside the
domain may happen to use the same IPv4 fragmentation identifier,
resulting in incorrect reassembly of the fragments at the destination
host. Given that the IPv4 fragmentation identifier is a 16 bit
field, it can be used similarly to port ranges. Thus, a MAP CE
SHOULD rewrite the IPv4 fragmentation identifier to a value
equivalent to a port of its allocated port-set.
11. NAT44 Considerations
The NAT44 implemented in the MAP CE SHOULD conform with the behavior
and best current practice documented in [RFC4787], [RFC5508], and
[RFC5382]. In MAP address sharing mode (determined by the MAP domain
/rule configuration parameters) the operation of the NAT44 MUST be
restricted to the available port numbers derived via the basic
mapping rule.
12. Usage Considerations
12.1. EA-bit length 0
The MAP solution supports use and configuration of domains where a
BMR expresses an EA-bit length of 0. This results in independence
between the IPv6 prefix assigned to the CE and the IPv4 address and/
or port-range used by MAP. The k-bits of PSID information may in
this case be derived from the BMR.
The constraint imposed is that each such MAP domain be composed of
just 1 MAP CE which has a predetermined IPv6 end-user prefix. The BR
would be configured with an FMR for each such CPE, where the rule
would uniquely associate the IPv4 address + optional PSID and the
IPv6 prefix of that given CE.
12.2. Mesh and Hub and spoke modes
The hub and spoke mode of communication, whereby all traffic sent by
a MAP-T CE is forwarded via a BR, and the mesh mode, whereby a CE is
directly able to forward traffic to another CE, are governed by the
activation of Forward Mapping Rule that cover the IPv4-prefix
destination, and port-index range. By default, a MAP CE configured
only with a BMR, as per this specification, will use it to configure
its IPv4 parameters and IPv6 MAP address without enabling mesh mode.
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12.3. Communication with IPv6 servers in the MAP-T domain
By default, MAP-T allows communication between both IPv4-only and any
IPv6 enabled devices, as well as with native IPv6-only servers
provided that the servers are configured with an IPv4-mapped IPv6
address. This address could be part of the IPv6 prefix used by the
DMR in the MAP-T domain. Such IPv6 servers (e.g. An HTTP server, or
a web content cache device) are thus able to serve both IPv6 users as
well as IPv4-only users alike utilizing IPv6. Any such IPv6-only
servers SHOULD have both A and AAAA records in DNS. DNS64 [RFC6147]
become required only when IPv6 servers in the MAP-T domain are
expected themselves to initiate communication to external IPv4-only
hosts.
12.4. Compatibility with other NAT64 solutions
The MAP-T CEs NAT64 function is by default compatible for use with
[RFC6146] stateful NAT64 devices that are placed in the operator's
network. In such a case the MAP-T CE's DMR prefix is configured to
correspond to the NAT64 device prefix. This in effect allows the use
of MAP-T CEs in environments that need to perform statistical
multiplexing of IPv4 addresses, while utilizing stateful NAT64
devices, and can take the role of a CLAT as defined in [RFC6877].
13. IANA Considerations
This specification does not require any IANA actions.
14. Security Considerations
Spoofing attacks: With consistency checks between IPv4 and IPv6
sources that are performed on IPv4/IPv6 packets received by MAP
nodes, MAP does not introduce any new opportunity for spoofing
attacks that would not already exist in IPv6.
Denial-of-service attacks: In MAP domains where IPv4 addresses are
shared, the fact that IPv4 datagram reassembly may be necessary
introduces an opportunity for DOS attacks. This is inherent to
address sharing, and is common with other address sharing
approaches such as DS-Lite and NAT64/DNS64. The best protection
against such attacks is to accelerate IPv6 support in both clients
and servers.
Routing-loop attacks: This attack may exist in some automatic
tunneling scenarios are documented in [RFC6324]. They cannot
exist with MAP because each BRs checks that the IPv6 source
address of a received IPv6 packet is a CE address based on
Forwarding Mapping Rule.
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Attacks facilitated by restricted port-set: From hosts that are not
subject to ingress filtering of [RFC2827], some attacks are
possible by an attacker injecting spoofed packets during ongoing
transport connections ([RFC4953], [RFC5961], [RFC6056]. The
attacks depend on guessing which ports are currently used by
target hosts, and using an unrestricted port-set is preferable,
i.e. Using native IPv6 connections that are not subject to MAP
port-range restrictions. To minimize this type of attacks when
using a restricted port set, the MAP CE's NAT44 filtering behavior
SHOULD be "Address-Dependent Filtering". Furthermore, the MAP CEs
SHOULD use a DNS transport proxy function to handle DNS traffic,
and source such traffic from IPv6 interfaces not assigned to MAP-
T. Practicalities of these methods are discussed in Section 5.9
of [I-D.dec-stateless-4v6].
ICMP Flooding Given the necessity to process and translate ICMP and
ICMPv6 messages by the BR and CE nodes, a foreseeable attack
vector is that of a flood of such messages leading to a saturation
of the node's ICMP computing resources. This attack vector is not
specific to MAP, and its mitigation lies a combination of policing
the rate of ICMP messages, policing the rate at which such
messages can get processed by the MAP nodes, and of course
identifying and blocking off the source(s) of such traffic.
[RFC6269] outlines general issues with IPv4 address sharing.
15. Contributors
The following individuals authored major contributions to this
document, and made the document possible:
Chongfeng Xie (China Telecom) Room 708, No.118, Xizhimennei Street
Beijing 100035 CN Phone: +86-10-58552116 Email: xiechf@ctbri.com.cn
Qiong Sun (China Telecom) Room 708, No.118, Xizhimennei Street
Beijing 100035 CN Phone: +86-10-58552936 Email: sunqiong@ctbri.com.cn
Rajiv Asati (Cisco Systems) 7025-6 Kit Creek Road Research Triangle
Park NC 27709 USA Email: rajiva@cisco.comc
Gang Chen (China Mobile) 53A,Xibianmennei Ave. Beijing 100053
P.R.China Email: chengang@chinamobile.com
Wentao Shang (CERNET Center/Tsinghua University) Room 225, Main
Building, Tsinghua University Beijing 100084 CN Email:
wentaoshang@gmail.com
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Guoliang Han (CERNET Center/Tsinghua University) Room 225, Main
Building, Tsinghua University Beijing 100084 CN Email:
bupthgl@gmail.com
Yu Zhai CERNET Center/Tsinghua University Room 225, Main Building,
Tsinghua University Beijing 100084 CN Email: jacky.zhai@gmail.com
16. Acknowledgements
This document is based on the ideas of many. In particular Remi
Despres, who has tirelessly worked on generalized mechanisms for
stateless address mapping.
The authors would also like to thank Mohamed Boucadair, Guillaume
Gottard, Dan Wing, Jan Zorz, Nejc Scoberne, Tina Tsou, Gang Chen,
Maoke Chen, Xiaohong Deng, Jouni Korhonen, Tomasz Mrugalski, Jacni
Qin, Chunfa Sun, Qiong Sun, Leaf Yeh, Andrew Yourtchenko, Roberta
Maglione and Hongyu Chen for their review and comments.
17. References
17.1. Normative References
[I-D.ietf-softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, "Mapping of Address and Port
with Encapsulation (MAP)", draft-ietf-softwire-map-12
(work in progress), November 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
[RFC6346] Bush, R., "The Address plus Port (A+P) Approach to the
IPv4 Address Shortage", RFC 6346, August 2011.
17.2. Informative References
[I-D.dec-stateless-4v6]
Dec, W., Asati, R., and H. Deng, "Stateless 4Via6 Address
Sharing", draft-dec-stateless-4v6-04 (work in progress),
October 2011.
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[I-D.ietf-softwire-map-dhcp]
Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
W., Bao, C., leaf.yeh.sdo@gmail.com, l., and X. Deng,
"DHCPv6 Options for configuration of Softwire Address and
Port Mapped Clients", draft-ietf-softwire-map-dhcp-11
(work in progress), November 2014.
[I-D.ietf-softwire-stateless-4v6-motivation]
Boucadair, M., Matsushima, S., Lee, Y., Bonness, O.,
Borges, I., and G. Chen, "Motivations for Carrier-side
Stateless IPv4 over IPv6 Migration Solutions", draft-ietf-
softwire-stateless-4v6-motivation-05 (work in progress),
November 2012.
[I-D.maglione-softwire-map-t-scenarios]
Maglione, R., Dec, W., Leung, I., and E. Mallette, "Use
cases for MAP-T", draft-maglione-softwire-map-
t-scenarios-05 (work in progress), October 2014.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC0897] Postel, J., "Domain name system implementation schedule",
RFC 897, February 1984.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC
2663, August 1999.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
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[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", RFC
4953, July 2007.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
[RFC5961] Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
Robustness to Blind In-Window Attacks", RFC 5961, August
2010.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056, January
2011.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
April 2011.
[RFC6219] Li, X., Bao, C., Chen, M., Zhang, H., and J. Wu, "The
China Education and Research Network (CERNET) IVI
Translation Design and Deployment for the IPv4/IPv6
Coexistence and Transition", RFC 6219, May 2011.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, June
2011.
[RFC6324] Nakibly, G. and F. Templin, "Routing Loop Attack Using
IPv6 Automatic Tunnels: Problem Statement and Proposed
Mitigations", RFC 6324, August 2011.
[RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
Combination of Stateful and Stateless Translation", RFC
6877, April 2013.
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Appendix A. Examples of MAP-T translation
Example 1 - Basic Mapping Rule:
Given the following MAP domain information and IPv6 end-user
prefix assigned to a MAP CE:
End-user IPv6 prefix: 2001:db8:0012:3400::/56
Basic Mapping Rule: {2001:db8:0000::/40 (Rule IPv6 prefix),
192.0.2.0/24 (Rule IPv4 prefix),
16 (Rule EA-bits length)}
PSID length: (16 - (32 - 24) = 8. (Sharing ratio of 256)
PSID offset: 6 (default)
A MAP node (CE or BR) can via the BMR, or equivalent FMR,
determine the IPv4 address and port-set as shown below:
EA bits offset: 40
IPv4 suffix bits (p): Length of IPv4 address (32) - IPv4 prefix
length (24) = 8
IPv4 address: 192.0.2.18 (0xc0000212)
PSID start: 40 + p = 40 + 8 = 48
PSID length (q): o - p = (End-user prefix len -
rule IPv6 prefix len) - p
= (56 - 40) - 8 = 8
PSID: 0x34
Available ports (63 ranges): 1232-1235, 2256-2259, ...... ,
63696-63699, 64720-64723
The BMR information allows a MAP CE to determine (complete)
its IPv6 address within the indicated end-user IPv6 prefix.
IPv6 address of MAP CE: 2001:db8:0012:3400:0000:c000:0212:0034
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Example 2 - BR:
Another example can be made of a MAP-T BR,
configured with the following FMR when receiving a packet
with the following characteristics:
IPv4 source address: 10.2.3.4 (0x0a020304)
TCP source port: 80
IPv4 destination address: 192.0.2.18 (0xc0000212)
TCP destination port: 1232
Forwarding Mapping Rule: {2001:db8::/40 (Rule IPv6 prefix),
192.0.2.0/24 (Rule IPv4 prefix),
16 (Rule EA-bits length)}
MAP-T BR Prefix (DMR): 2001:db8:ffff::/64
The above information allows the BR to derive as follows
the mapped destination IPv6 address for the corresponding
MAP-T CE, and also the source IPv6 address for
the mapped IPv4 source address.
IPv4 suffix bits (p): 32 - 24 = 8 (18 (0x12))
PSID length: 8
PSID: 0 x34 (1232)
The resulting IPv6 packet will have the following header fields:
IPv6 source address: 2001:db8:ffff:0:000a:0203:0400::
IPv6 destination address: 2001:db8:0012:3400:0000:c000:0212:0034
TCP source Port: 80
TCP destination Port: 1232
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Example 3- FMR:
An IPv4 host behind a MAP-T CE (configured as per the previous
examples) corresponding with an IPv4 host 10.2.3.4 will have its
packets converted into IPv6 using the DMR configured on the MAP-T
CE as follows:
Default Mapping Rule: {2001:db8:ffff::/64 (Rule IPv6 prefix),
0.0.0.0/0 (Rule IPv4 prefix)}
IPv4 source address: 192.0.2.18
IPv4 destination address: 10.2.3.4
IPv4 source port: 1232
IPv4 destination port: 80
MAP-T CE IPv6 source address: 2001:db8:0012:3400:0000:c000:0212:0034
IPv6 destination address: 2001:db8:ffff:0:000a:0203:0400::
Example 4 - Rule with no embedded address bits and no address sharing
End-user IPv6 prefix: 2001:db8:0012:3400::/56
Basic Mapping Rule: {2001:db8:0012:3400::/56 (Rule IPv6 prefix),
192.0.2.1/32 (Rule IPv4 prefix),
0 (Rule EA-bits length)}
PSID length: 0 (Sharing ratio is 1)
PSID offset: n/a
A MAP node can via the BMR or equivalent FMR, determine
the IPv4 address and port-set as shown below:
EA bits offset: 0
IPv4 suffix bits (p): Length of IPv4 address - IPv4 prefix
length = 32 - 32 = 0
IPv4 address: 192.0.2.18 (0xc0000212)
PSID start: 0
PSID length: 0
PSID: null
The BMR information allows a MAP CE also to determine (complete)
its full IPv6 address by combining the IPv6 prefix with the MAP
interface identifier (that embeds the IPv4 address).
IPv6 address of MAP CE: 2001:db8:0012:3400:0000:c000:0201:0000
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Example 5 - Rule with no embedded address bits and address sharing
(sharing ratio 256)
End-user IPv6 prefix: 2001:db8:0012:3400::/56
Basic Mapping Rule: {2001:db8:0012:3400::/56 (Rule IPv6 prefix),
192.0.2.18/32 (Rule IPv4 prefix),
0 (Rule EA-bits length)}
PSID length: (16 - (32 - 24)) = 8. Sharing ratio of 256.
Provisioned with DHCPv6.
PSID offset: 6 (default)
PSID: 0x20 (Provisioned with DHCPv6)
A MAP node can via the BMR determine the IPv4 address and port-set
as shown below:
EA bits offset: 0
IPv4 suffix bits (p): Length of IPv4 address - IPv4 prefix
length = 32 -32 = 0
IPv4 address 192.0.2.18 (0xc0000212)
PSID start: 0
PSID length: 8
PSID: 0x34
Available ports (63 ranges) : 1232-1235, 2256-2259, ...... ,
63696-63699, 64720-64723
The BMR information allows a MAP CE also to determine (complete)
its full IPv6 address by combining the IPv6 prefix with the MAP
interface identifier (that embeds the IPv4 address and PSID).
IPv6 address of MAP CE: 2001:db8:0012:3400:0000:c000:0212:0034
Note that the IPv4 address and PSID is not derived from the IPv6
prefix assigned to the CE, but provisioned separately using for
example MAP options in DHCPv6.
Appendix B. Port mapping algorithm
The driving principles and the mathematical expression of the mapping
algorithm used by MAP can be found in Appendix B of
[I-D.ietf-softwire-map]
Authors' Addresses
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Xing Li
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Email: xing@cernet.edu.cn
Congxiao Bao
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Email: congxiao@cernet.edu.cn
Wojciech Dec (editor)
Cisco Systems
Haarlerbergpark Haarlerbergweg 13-19
Amsterdam, NOORD-HOLLAND 1101 CH
Netherlands
Email: wdec@cisco.com
Ole Troan
Cisco Systems
Oslo
Norway
Email: ot@cisco.com
Satoru Matsushima
SoftBank Telecom
1-9-1 Higashi-Shinbashi, Munato-ku
Tokyo
Japan
Email: satoru.matsushima@tm.softbank.co.jp
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Tetsuya Murakami
IP Infusion
1188 East Arques Avenue
Sunnyvale
USA
Email: tetsuya@ipinfusion.com
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