Internet DRAFT - draft-ietf-lisp-signal-free-multicast
draft-ietf-lisp-signal-free-multicast
Network Working Group V. Moreno
Internet-Draft Cisco Systems
Intended status: Experimental D. Farinacci
Expires: September 9, 2018 lispers.net
March 8, 2018
Signal-Free LISP Multicast
draft-ietf-lisp-signal-free-multicast-09
Abstract
When multicast sources and receivers are active at LISP sites, the
core network is required to use native multicast so packets can be
delivered from sources to group members. When multicast is not
available to connect the multicast sites together, a signal-free
mechanism can be used to allow traffic to flow between sites. The
mechanism within here uses unicast replication and encapsulation over
the core network for the data-plane and uses the LISP mapping
database system so encapsulators at the source LISP multicast site
can find decapsulators at the receiver LISP multicast sites.
Requirements Language
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 [RFC2119].
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://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 September 9, 2018.
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Copyright Notice
Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 5
4. General Procedures . . . . . . . . . . . . . . . . . . . . . 7
4.1. General Receiver-Site Procedures . . . . . . . . . . . . 8
4.1.1. Multicast Receiver Detection . . . . . . . . . . . . 8
4.1.2. Receiver-Site Registration . . . . . . . . . . . . . 8
4.1.3. Consolidation of the Replication-List . . . . . . . . 9
4.2. General Source-Site Procedures . . . . . . . . . . . . . 10
4.2.1. Multicast Tree Building at the Source-Site . . . . . 10
4.2.2. Multicast Destination Resolution . . . . . . . . . . 10
4.3. General LISP Notification Procedures . . . . . . . . . . 11
5. Source Specific Multicast Trees . . . . . . . . . . . . . . . 11
5.1. Source Directly Connected to Source-ITRs . . . . . . . . 12
5.2. Source not Directly Connected to Source-ITRs . . . . . . 12
6. Multi-Homing Considerations . . . . . . . . . . . . . . . . . 12
6.1. Multiple ITRs at a Source-Site . . . . . . . . . . . . . 12
6.2. Multiple ETRs at a Receiver-Site . . . . . . . . . . . . 13
6.3. Multiple RLOCs for an ETR at a Receiver-Site . . . . . . 13
6.4. Multicast RLOCs for an ETR at a Receiver-Site . . . . . . 14
7. PIM Any Source Multicast Trees . . . . . . . . . . . . . . . 14
8. Signal-Free Multicast for Replication Engineering . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Document Change Log . . . . . . . . . . . . . . . . 21
A.1. Changes to draft-ietf-lisp-signal-free-multicast-09 . . . 21
A.2. Changes to draft-ietf-lisp-signal-free-multicast-08 . . . 21
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A.3. Changes to draft-ietf-lisp-signal-free-multicast-07 . . . 21
A.4. Changes to draft-ietf-lisp-signal-free-multicast-06 . . . 21
A.5. Changes to draft-ietf-lisp-signal-free-multicast-05 . . . 21
A.6. Changes to draft-ietf-lisp-signal-free-multicast-04 . . . 22
A.7. Changes to draft-ietf-lisp-signal-free-multicast-03 . . . 22
A.8. Changes to draft-ietf-lisp-signal-free-multicast-02 . . . 22
A.9. Changes to draft-ietf-lisp-signal-free-multicast-01 . . . 22
A.10. Changes to draft-ietf-lisp-signal-free-multicast-00 . . . 23
A.11. Changes to draft-farinacci-lisp-signal-free-multicast-04 23
A.12. Changes to draft-farinacci-lisp-signal-free-multicast-03 23
A.13. Changes to draft-farinacci-lisp-signal-free-multicast-02 23
A.14. Changes to draft-farinacci-lisp-signal-free-multicast-01 23
A.15. Changes to draft-farinacci-lisp-signal-free-multicast-00 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
When multicast sources and receivers are active at LISP sites, and
the core network between the sites does not provide multicast
support, a signal-free mechanism can be used to create an overlay
that will allow multicast traffic to flow between sites and connect
the multicast trees at the different sites.
The signal-free mechanism proposed here does not extend PIM [RFC7761]
over the overlay as proposed in [RFC6831], nor does the mechanism
utilize direct signaling between the Receiver-ETRs and Sender-ITRs as
described in [I-D.farinacci-lisp-mr-signaling]. The signal-free
mechanism proposed reduces the amount of signaling required between
sites to a minimum and is centered around the registration of
Receiver-sites for a particular multicast-group or multicast-channel
with the LISP Mapping System.
Registrations from the different receiver-sites will be merged at the
Mapping System to assemble a multicast-replication-list inclusive of
all RLOCs that lead to receivers for a particular multicast-group or
multicast-channel. The replication-list for each specific multicast-
entry is maintained as a database mapping entry in the LISP Mapping
System.
When the ITR at the source-site receives multicast traffic from
sources at its site, the ITR can query the mapping system by issuing
Map-Request messages for the (S,G) source and destination addresses
in the packets received. The Mapping System will return the RLOC
replication-list to the ITR, which the ITR will cache as per standard
LISP procedure. Since the core is assumed to not support multicast,
the ITR will replicate the multicast traffic for each RLOC on the
replication-list and will unicast encapsulate the traffic to each
RLOC. The combined function or replicating and encapsulating the
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traffic to the RLOCs in the replication-list is referred to as "rep-
encapsulation" in this document.
The document describes the General Procedures (Section 4) and
information encoding that are required at the Receiver-sites and
Source-sites to achieve signal-free multicast interconnectivity. The
General Procedures for Mapping System Notifications to different
sites are also described. A section dedicated to the specific case
of SSM trees discusses the implications to the General Procedures for
SSM multicast trees over different topological scenarios. A section
on ASM support is included to identify the constraints that come
along with supporting it using LISP Signal-Free multicast.
There is a section dedicated to Replication Engineering. A mechanism
to reduce the impact of head-end replication. The mapping system,
via LISP Signal-Free mechanisms, can be used to build a layer of
RTRs.
2. Definition of Terms
LISP related terms, notably Map-Request, Map-Reply, Ingress Tunnel
Router (ITR), Egress Tunnel Router (ETR), Map-Server (MS) and Map-
Resolver (MR) are defined in the LISP specification [RFC6830].
Extensions to the definitions in [RFC6830] for their application to
multicast routing are documented in [RFC6831].
Terms defining interactions with the LISP Mapping System are defined
in [RFC6833].
The following terms are consistent with the definitions in [RFC6830]
and [RFC6831]. The terms are specific cases of the general terms and
are here defined to facilitate the descriptions and discussions
within this particular document.
Source: Multicast source end-point. Host originating multicast
packets.
Receiver: Multicast group member end-point. Host joins multicast
group as a receiver of multicast packets sent to the group.
Receiver-site: LISP site where multicast receivers are located.
Source-site: LISP site where multicast sources are located.
RP-site: LISP site where an ASM PIM Rendezvous Point [RFC7761] is
located. The RP-site and the Source-site MAY be the same in some
situations.
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Receiver-ETR: LISP decapsulating xTR at the Receiver-site. This is a
multicast ETR.
Source-ITR: LISP encapsulating xTR at the Source-site. This is a
multicast ITR.
RP-xTR: LISP xTR at the RP-site. This is typically a multicast ITR.
Replication-list: Mapping-entry containing the list of RLOCs that
have registered Receivers for a particular multicast-entry.
Multicast-entry: A tuple identifying a multicast tree. Multicast-
entries are in the form of (S-prefix, G-prefix).
Rep-encapsulation: The process of replicating and then encapsulating
traffic to multiple RLOCs.
Re-encapsulating Tunnel Router (RTR): An RTR is a router that
implements the re-encapsulating tunnel function detailed in Section 8
of the main LISP specification [RFC6830]. A LISP RTR performs packet
re-routing by chaining ETR and ITR functions, whereby it first
removes the LISP header of an ingress packet and then prepends a new
LISP header to an egress packet.
RTR Level: An RTR level is encoded in a Replication-List-Entry (RLE)
LCAF Type detailed in [RFC8060]. Each entry in the replication list
contains an address of an xTR and a level value. Level values are
used to create a replication hierarchy so that ITRs at source LISP
sites replicate to the lowest (smaller value) level number RTRs in a
RLE entry. And then RTRs at a given level replicate to the next
higher level of RTRs. The number of RTRs at each level are
engineered to control the fan-out or replication factor so a tradeoff
between the width of the level versus the number of levels can be
selected.
ASM: Any-Source Multicast as defined in [RFC3569] and [RFC7761] where
multicast distribution trees are built with a Rendezvous Point.
SSM: Source Specific Multicast as defined in [RFC3569] where
multicast distribution trees are built and rooted at the multicast
router(s) directly connected to the multicast source.
3. Reference Model
The reference model that will be used for the discussion of the
Signal-Free multicast tree interconnection is illustrated in
Figure 1.
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MS/MR
+---+
| |
+---+ +---+ +---+ +---+ +---+
Src-1 ----| R1|-----|ITR| | |ETR|------| R2|------ Rcv-2
+---+ +---+ | +---+ +---+
\ | /
Source-site-1 \ | / Receiver-site-2
\ | /
\ | /
\ | /
Core
/ \
/ \
/ \
/ \
/ \
+---+ +---+
Src-3 --------------|ITR| |ETR|----------------- Rcv-4
+---+ +---+
Source-site-3 Receiver-site-4
Figure 1: LISP Multicast Generic Reference Model
Sites 1 and 3 are Source-sites.
Source-site-3 presents a Source (Src-3) that is directly connected to
the Source-ITR
Source-site-1 presents a Source (Src-1) that is one hop or more away
from the Source-ITR
Receiver-site-2 and 4 are receiver sites with not-directly connected
and directly connected Receiver end-points respectively
R1 is a multicast router in Source-site-1.
R2 is a multicast router at the Receiver-site.
The Map-Servers and Resolvers are reachable in the RLOC space in the
Core, only one is shown for illustration purposes, but these can be
many or even part of a Distributed Mapping System, such as a DDT
Tree.
The procedures for interconnecting multicast Trees over an overlay
can be broken down into three functional areas:
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o Receiver-site procedures
o Source-site procedures
o LISP notification procedures
The receiver site procedures will be common for most tree types and
topologies.
The procedures at the source site can vary depending on the type of
trees being interconnected as well as based on the topological
relation between sources and source-site xTRs. For ASM trees, a
special case of the Source-site is the RP-site for which a variation
of the Source-site procedures MAY be necessary if ASM trees are to be
supported in future specifications of LISP Signal-Free multicast.
The LISP notification procedures between sites are normalized for the
different possible scenarios. Certain scenarios MAY benefit from a
simplified notification mechanism or no notification requirement at
all.
4. General Procedures
The interconnection of multicast trees across different LISP sites
involves the following procedures to build the necessary multicast
distribution trees across sites.
1. The presence of multicast Receiver end-points is detected by the
Receiver-ETRs at the Receiver-sites.
2. Receiver-ETRs register their RLOCs as part of the replication-
list for the multicast-entry the detected Receivers subscribe to.
3. The Mapping-system merges all receiver-ETR or delivery-group
RLOCs to build a comprehensive replication-list inclusive of all
Receiver-sites for each multicast-entry.
4. LISP Map-Notify messages MUST be sent to the Source-ITR informing
of any changes in the replication-list.
5. Multicast-tree building at the Source-site is initiated when the
Source-ITR receives the LISP Notification.
Once the multicast distribution trees are built, the following
forwarding procedures may take place:
1. The Source sends multicast packets to the multicast group
destination address.
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2. Multicast traffic follows the multicast tree built at the Source-
site and makes its way to the Source-ITRs.
3. The Source-ITR will issue a map-request to resolve the
replication-list for the multicast-entry.
4. The Mapping System responds to the Source-ITR with a map-reply
containing the replication-list for the multicast group
requested.
5. The Source-ITR caches the replication-list received in the map-
reply for the multicast-entry.
6. Multicast traffic is rep-encapsulated. That is, the packet is
replicated for each RLOC in the replication-list and then
encapsulated to each one.
4.1. General Receiver-Site Procedures
4.1.1. Multicast Receiver Detection
When the Receiver-ETRs are directly connected to the Receivers (e.g.
Receiver-site-4 in Figure 1), the Receiver-ETRs will receive IGMP
Reports from the Receivers indicating which group the Receivers wish
to subscribe to. Based on these IGMP Reports, the receiver-ETR is
made aware of the presence of Receivers as well as which group they
are interested in.
When the Receiver-ETRs are several hops away from the Receivers (e.g.
Receiver-site-2 in Figure 1), the Receiver-ETRs will receive PIM join
messages which will allow the Receiver-ETR to know that there are
multicast Receivers at the site and also learn which multicast group
the Receivers are for.
4.1.2. Receiver-Site Registration
Once the Receiver-ETRs detect the presence of Receivers at the
Receiver-site, the Receiver-ETRs MUST issue Map-Register messages to
include the Receiver-ETR RLOCs in the replication-list for the
multicast-entry the Receivers joined.
The Map-Register message MUST use the multicast-entry (Source, Group)
tuple as its EID record type with the Receiver-ETR RLOCs conforming
the locator set.
The EID in the Map-Register message MUST be encoded using the
Multicast Information LCAF type defined in [RFC8060].
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The RLOC in the Map-Register message MUST be encoded using the
Replication List Entry (RLE) LCAF type defined in [RFC8060] with the
Level Value fields for all entries set to 128 (decimal).
The encoding described above MUST be used consistently for Map-
Register messages, entries in the Mapping System, Map-reply messages
as well as the map-cache at the Source-ITRs.
The Map-Register messages [RFC6830] sent by the receiver-ETRs MUST
have the following bits set as here specified:
1. merge-request-bit set to 1. The Map-Register messages are sent
with "Merge Semantics". The Map-Server will receive
registrations from a multitude of Receiver-ETRs. The Map-Server
will merge the registrations for common EIDs and maintain a
consolidated replication-list for each multicast-entry.
2. want-map-notify-bit (M) set to 0. This tells the Mapping System
that the receiver-ETR does not expect to receive Map-Notify
messages as it does not need to be notified of all changes to the
replication-list.
3. proxy-reply-bit (P) set to 1. The merged replication-list is
kept in the Map-Servers. By setting the proxy-reply bit, the
receiver-ETRs instruct the Mapping-system to proxy reply to map-
requests issued for the multicast entries.
Map-Register messages for a particular multicast-entry MAY be sent
for every receiver detected, even if previous receivers have been
detected for the particular multicast-entry. This allows the
replication-list to remain up to date.
Receiver-ETRs MUST be configured to know what Map-Servers Map-
Register messages are sent to. The configuration is likely to be
associated with an S-prefix that multiple (S,G) entries match to and
are more specific for. Therefore, the S-prefix determines the Map-
Server set in the least number of configuration statements.
4.1.3. Consolidation of the Replication-List
The Map-Server will receive registrations from a multitude of
Receiver-ETRs. The Map-Server will merge the registrations for
common EIDs and consolidate a replication-list for each multicast-
entry.
When an ETR sends an RLE RLOC-record in a Map-Register and the RLE
entry already exists in the Map-Server's RLE merged list, the Map-
Server will replace the single RLE entry with the information from
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the Map-Register RLOC-record. The Map-Server MUST NOT merge
duplicate RLOCs in the consolidated replication-list.
4.2. General Source-Site Procedures
Source-ITRs MUST register the unicast EIDs of any Sources or
Rendezvous Points that may be present on the Source-site. In other
words, it is assumed that the Sources and RPs are LISP EIDs.
The registration of the unicast EIDs for the Sources or Rendezvous
Points allows the Map-Server to know where to send Map-Notify
messages to. Therefore, the Source-ITR MUST register the unicast
S-prefix EID with the want-map-notify-bit set in order to receive
Map-Notify messages whenever there is a change in the replication-
list.
4.2.1. Multicast Tree Building at the Source-Site
When the source site receives the Map-Notify messages from the
mapping system as described in Section 4.3, it will initiate the
process of building a multicast distribution tree that will allow the
multicast packets from the Source to reach the Source-ITR.
The Source-ITR MUST issue a PIM join for the multicast-entry for
which it received the Map-Notify message. The join will be issued in
the direction of the source or in the direction of the RP for the SSM
and ASM cases respectively.
4.2.2. Multicast Destination Resolution
On reception of multicast packets, the source-ITR obtains the
replication-list for the (S,G) addresses in the packets.
In order to obtain the replication-list, the Source-ITR MUST issue a
Map-Request message in which the EID is the (S,G) multicast tuple
which is encoded using the Multicast Info LCAF type defined in
[RFC8060].
The Mapping System (most likely the Map-Server) will Map-reply with
the merged replication-list maintained in the Mapping System. The
Map-reply message MUST follow the format defined in [RFC6830], its
EID is encoded using the Multicast Info LCAF type and the
corresponding RLOC-records are encoded using the RLE LCAF type. Both
LCAF types defined in [RFC8060].
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4.3. General LISP Notification Procedures
The Map-Server will issue LISP Map-Notify messages to inform the
Source-site of the presence of receivers for a particular multicast
group over the overlay.
Updated Map-Notify messages SHOULD be issued every time a new
registration is received from a Receiver-site. This guarantees that
the source-sites are aware of any potential changes in the multicast-
distribution-list membership.
The Map-Notify messages carry (S,G) multicast EIDs encoded using the
Multicast Info LCAF type defined in [RFC8060].
Map-Notify messages will be sent by the Map-Server to the RLOCs with
which the unicast S-prefix EID was registered. In the case when
sources are discovered dynamically [I-D.ietf-lisp-eid-mobility], xTRs
MUST register sources explicitly with the want-map-notify-bit set.
This is so the ITR in the site the source has moved to can get the
most current replication list.
When both the Receiver-sites and the Source-sites register to the
same Map-Server, the Map-Server has all the necessary information to
send the Map-Notify messages to the Source-site.
When the Map-Servers are distributed (when using LISP-DDT [RFC8111]),
the Receiver-sites MAY register to one Map-Server while the Source-
site registers to a different Map-Server. In this scenario, the Map-
Server for the receiver sites MUST resolve the unicast S-prefix EID
across a distributed mapping transport system, per standard LISP
lookup procedures and obtain the necessary information to send the
Map-Notify messages to the Source-site. The Map-Notify messages are
sent with an authentication length of 0 as they would not be
authenticated.
When the Map-Servers are distributed, different Receiver-sites MAY
register to different Map-Servers. However, this is not supported
with the currently defined mechanisms.
5. Source Specific Multicast Trees
The interconnection of Source Specific Multicast (SSM) Trees across
sites will follow the General Receiver-site Procedures described in
Section 4.1 on the Receiver-sites.
The Source-site Procedures will vary depending on the topological
location of the Source within the Source-site as described in
Section 5.1 and Section 5.2 .
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5.1. Source Directly Connected to Source-ITRs
When the Source is directly connected to the source-ITR, it is not
necessary to trigger signaling to build a local multicast tree at the
Source-site. Therefore Map-Notify messages are not required to
initiate building of the multicast tree at the Source-site.
Map-Notify messages are still required to ensure that any changes to
the replication-list are communicated to the Source-site so that the
map-cache at the Source-ITRs is kept updated.
5.2. Source not Directly Connected to Source-ITRs
The General LISP Notification Procedures described in Section 4.3
MUST be followed when the Source is not directly connected to the
source-ITR. On reception of Map-Notify messages, local multicast
signaling MUST be initiated at the Source-site per the General Source
Site Procedures for Multicast Tree building described in
Section 4.2.1.
In the SSM case, the IP address of the Source is known and it is also
registered with the LISP mapping system. Thus, the mapping system
MAY resolve the mapping for the Source address in order to send Map-
Notify messages to the correct source-ITR.
6. Multi-Homing Considerations
6.1. Multiple ITRs at a Source-Site
When multiple ITRs exist at a source multicast site, care MUST be
taken that more than one ITR does not head-end replicate packets else
receiver multicast sites will receive duplicate packets. The
following procedures will be used for each topology scenarios:
o When more than one ITR is directly connected to the source host,
either the PIM DR or the IGMP querier (when PIM is not enabled on
the ITRs) is responsible for packet replication. All other ITRs
silently drop the packet. In the IGMP querier case, one or more
ITRs on the source LAN MUST be IGMP querier candidates.
Therefore, it is required they are configured as such.
o When more than one ITR is multiple hops away from the source host
and one of the ITRs is the PIM Rendezvous Point, then the PIM RP
is responsible for packet replication.
o When more than one ITR is multiple hops away from the source host
and the PIM Rendezvous Point is not one of the ITRs, then one of
the ITRs MUST join to the RP. When a Map-Notify is received from
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the Map-Server by an ITR, only the highest RLOC addressed ITR will
join toward the PIM RP or toward the source.
6.2. Multiple ETRs at a Receiver-Site
When multiple ETRs exist in a receiver multicast site, and each
create multicast join state, they each Map-Register their RLOC
addresses to the mapping system. In this scenario, the replication
happens on the overlay causing multiple ETR entry points to replicate
to all receivers versus a single ETR entry point replicating to all
receivers. If an ETR does not create join state, because it has not
received PIM joins or IGMP reports, it will not Map-Register its RLOC
addresses to the mapping system. The same procedures in Section 4.1
are followed.
When multiple ETRs exist on the same LAN as a receiver host, then the
PIM DR, when PIM is enabled, or the IGMP querier is responsible for
sending a Map-Register for its RLOC. In the IGMP case, one or more
ETRs on LAN MUST be IGMP querier candidates. Therefore, it is
required they are configured as such.
6.3. Multiple RLOCs for an ETR at a Receiver-Site
It MAY be desirable to have multiple underlay paths to an ETR for
multicast packet delivery. This can be done by having multiple RLOCs
assigned to an ETR and having the ETR send Map-Registers for all its
RLOCs. By doing this, an ITR can choose a specific path based on
underlay performance and/or RLOC reachability.
It is recommended that an ETR sends a Map-Register with a single
RLOC-record that uses the ELP LCAF type [RFC8060] that is nested
inside RLE entry LCAF. For example say ETR1 has assigned RLOC1 and
RLOC2 for a LISP receiver site. And there is ETR2 in another LISP
receiver site, that has RLOC3. The two receiver sites have the same
(S,G) being joined. Here is how the RLOC-record is encoded on each
ETR:
ETR1: EID-record: (S,G)
RLOC-record: RLE[ ELP{ (RLOC1,s,p), (RLOC2,s,p) } ]
ETR2: EID-record: (S,G)
RLOC-record: RLE[ RLOC3 ]
And here is how the entry is merged and stored on the Map-Server
since the Map-Registers have an RLE encoded RLOC-record:
MS: EID-record: (S,G)
RLOC-record: RLE[ RLOC3, ELP{ (RLOC1,s,p), (RLOC2,s,p) } ]
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When the ITR receives a packet from a multicast source S for group G,
it uses the merged RLOC-record, returned from the Map-Server. The
ITR replicates the packet to (RLOC3 and RLOC1) or (RLOC3 and RLOC2).
Since it is required for the s-bit to be set for RLOC1, the ITR MUST
replicate to RLOC1 if it is reachable. When the required p-bit is
also set, the RLOC-reachability mechanisms from [RFC6830] are
followed. If the ITR determines that RLOC1 is unreachable, it uses
RLOC2, as long as RLOC2 is reachable.
6.4. Multicast RLOCs for an ETR at a Receiver-Site
This specification is focused on underlays without multicast support,
but does not preclude the use of multicast RLOCs in RLE entries.
ETRs MAY register multicast EID entries using multicast RLOCs. In
such cases the ETRs will get joined to underlay multicast
distribution trees by using IGMP as a multicast host using mechanisms
in [RFC2236] and [RFC3376].
7. PIM Any Source Multicast Trees
LISP signal-free multicast can support ASM Trees in limited but
acceptable topologies. It is suggested for the simplification of
building ASM trees across the LISP overlay to have PIM-ASM run
independently in each LISP site. What this means, is that a PIM
Rendezvous Point (RP) is configured in each LISP site so PIM Register
procedures and (*,G) state maintenance is contained within the LISP
site.
The following procedure will be used to support ASM in each LISP
site:
1. In a Receiver-site, the RP is colocated with the ETR. RPs for
different groups can be spread across each ETR, but is not
required.
2. When (*,G) state is created in an ETR, the procedures in
Section 4.1.2 are followed. In addition, the ETR registers
(S-prefix,G), where S-prefix is 0/0 (the respective unicast
default route for the address-family) to the mapping system.
3. In a Source-site, the RP is colocated with the ITR. RPs for
different groups can be spread across each ITR, but is not
required.
4. When a multicast source sends a packet, a PIM Register message is
delivered to the ITR and the procedures in Section 4.2 are
followed.
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5. When the ITR sends a Map-Request for (S,G) and no Receiver-site
has registered for (S,G), the mapping system will return the
(0/0,G) entry to the ITR so it has a replication list of all the
ETRs that have received (*,G) state.
6. The ITR stores the replication-list in its map-cache for (S,G).
It replicates packets to all ETRs in the list.
7. ETRs decapsulate packets and forward based on (*,G) state in
their site.
8. When last-hop PIM routers join the newly discovered (S,G), the
ETR will store the state and follow the procedures in
Section 4.1.2.
8. Signal-Free Multicast for Replication Engineering
The mechanisms in this draft can be applied to the LISP Replication-
Engineering [I-D.coras-lisp-re] design. Rather than having the
layered LISP-RE RTR hierarchy use signaling mechanisms, the RTRs can
register their availability for multicast tree replication via the
mapping database system.
As stated in [I-D.coras-lisp-re], the RTR layered hierarchy is used
to avoid head-end replication in replicating nodes closest to a
multicast source. Rather than have multicast ITRs replicate to each
ETR in an RLE entry of a (S,G) mapping database entry, it could
replicate to one or more layer-0 RTRs in the LISP-RE hierarchy.
This draft documents how the RTR hierarchy is determined but not what
are the optimal layers of RTRs to use. Methods for determining
optimal paths or RTR topological closeness are out of scope for his
document.
There are two formats an (S,G) mapping database entry could have.
One format is a 'complete-format' and the other is a 'filtered-
format'. A 'complete-format' entails an (S,G) entry having multiple
RLOC records which contain both ETRs that have registered as well as
the RTRs at the first level of the LISP-RE hierarchy for the ITR to
replicate to. When using 'complete-format', the ITR has the ability
to select if it replicates to RTRs or to the registered ETRs at the
receiver sites. A 'filtered-format' (S,G) entry is one where the
Map-Server returns the RLOC-records that it decides the ITR SHOULD
use. So replication policy is shifted from the ITRs to the mapping
system. The Map-Servers can also decide for a given ITR, if it uses
a different set of replication targets per (S,G) entry for which the
ITR is replicating for.
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The procedure for the LISP-RE RTRs to make themselves available for
replication can occur before or after any receivers join an (S,G)
entry or any sources send for a particular (S,G) entry. Therefore,
newly configured RTR state will be used to create new (S,G) state and
inherited into existing (S,G) state. A set of RTRs can register
themselves to the mapping system or a third-party can do so on their
behalf. When RTR registration occurs, it is done with an (S-prefix,
G-prefix) entry so it can advertise its replication services for a
wide-range of source/group combinations.
When a Map-Server receives (S,G) registrations from ETRs and
(S-prefix, G-prefix) registrations from RTRs, it has the option of
merging the RTR RLOC-records for each (S,G) that is more-specific for
the (S-prefix, G-prefix) entry or keep them separate. When merging,
a Map-Server is ready to return a 'complete-format' Map-Reply. When
keeping the entries separate, the Map-Server can decide what to
include in a Map-Reply when a Map-Request is received. It can
include a combination of RLOC-records from each entry or decide to
use one or the other depending on policy configured.
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+---+ +----+
Src-1 --------------|ITR| |ETR1|---------------- Rcv-1
+---+ +----+
\ /
Source-site-1 \ / Receiver-site-1
\ /
\ /
+----+ \ / +----+
|RTR1| \ / |RTR2| Level-0
+----+ \ / +----+
\ <^^^^^^^^^^^^^^> /
\ < > /
< Core-Network >
< >
<vvvvvvvvvvvvvv>
/ / \ \
/ / \ \
+----+ / / \ \ +----+
|RTR3| / \ |RTR4| Level-1
+----+ / \ +----+
/ \
/ \
+----+ +----+
Rcv-2 --------------|ETR2| |ETR3|---------------- Rcv-3
+----+ +----+
Receiver-site-2 Receiver-site-3
Figure 2: LISP-RE Reference Model
Here is a specific example, illustrated in Figure 2, of (S,G) and
(S-prefix, G-prefix) mapping database entries when a source S is
behind an ITR and there are receiver sites joined to (S,G) via ETR1,
ETR2, and ETR3. And there exists a LISP-RE hierarchy of RTR1 and
RTR2 at level-0 and RTR3 and RTR4 at level-1:
EID-record: (S,G)
RLOC-record: RLE: (ETR1, ETR2, ETR3), p1
EID-record: (S-prefix, G-prefix)
RLOC-record: RLE: (RTR1(L0), RTR2(L0), RTR3(L1), RTR4(L1)), p1
The above entries are in the form of how they were registered and
stored in a Map-Server. When a Map-Server uses 'complete-format', a
Map-Reply it originates has the mapping record encoded as:
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EID-record: (S,G)
RLOC-record: RLE: (RTR1(L0), RTR3(L1)), p1
RLOC-record: RLE: (ETR1, ETR2, ETR3), p1
The above Map-Reply allows the ITR to decide if it replicates to the
ETRs or if it SHOULD replicate only to level-0 RTR1. This decision
is left to the ITR since both RLOC-records have priority 1. If the
Map-Server wanted to force the ITR to replicate to RTR1, it would set
the ETRs RLOC-record to priority greater than 1.
When a Map_server uses "filtered-format', a Map-Reply it originates
has the mapping record encoded as:
EID-record: (S,G)
RLOC-record: RLE: (RTR1(L0), RTR3(L1)), p1
An (S,G) entry can contain alternate RTRs. So rather than
replicating to multiple RTRs, one of a RTR set MAY be used based on
the RTR reachability status. An ITR can test reachability status to
any layer-0 RTR using RLOC-probing so it can choose one RTR from a
set to replicate to. When this is done the RTRs are encoded in
different RLOC-records versus together in one RLE RLOC-record. This
moves the replication load off the ITRs at the source site to the
RTRs inside the network infrastructure. This mechanism can also be
used by level-n RTRs to level-n+1 RTRs.
The following mapping would be encoded in a Map-Reply sent by a Map-
Server and stored in the ITR. The ITR would use RTR1 until it went
unreachable and then switch to use RTR2:
EID-record: (S,G)
RLOC-record: RTR1, p1
RLOC-record: RTR2, p2
9. Security Considerations
[I-D.ietf-lisp-sec] defines a set of security mechanisms that provide
origin authentication, integrity and anti-replay protection to LISP's
EID-to-RLOC mapping data conveyed via mapping lookup process. LISP-
SEC also enables verification of authorization on EID-prefix claims
in Map-Reply messages.
Additional security mechanisms to protect the LISP Map-Register
messages are defined in [RFC6833].
The security of the Mapping System Infrastructure depends on the
particular mapping database used. The [RFC8111] specification, as an
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example, defines a public-key based mechanism that provides origin
authentication and integrity protection to the LISP DDT protocol.
Map-Replies received by the source-ITR can be signed (by the Map-
Server) so the ITR knows the replication-list is from a legit source.
Data-plane encryption can be used when doing unicast rep-
encapsulation as described in [RFC8061].
10. IANA Considerations
This document has no IANA implications
11. Acknowledgements
The authors want to thank Greg Shepherd, Joel Halpern and Sharon
Barkai for their insightful contribution to shaping the ideas in this
document. A special thanks to Luigi Iannone, LISP WG co-chair, for
shepherding this working group document. Thanks also goes to Jimmy
Kyriannis, Paul Vinciguerra, Florin Coras, and Yan Filyurin for
testing an implementation of this draft.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
<https://www.rfc-editor.org/info/rfc2236>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>.
[RFC3569] Bhattacharyya, S., Ed., "An Overview of Source-Specific
Multicast (SSM)", RFC 3569, DOI 10.17487/RFC3569, July
2003, <https://www.rfc-editor.org/info/rfc3569>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
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[RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The
Locator/ID Separation Protocol (LISP) for Multicast
Environments", RFC 6831, DOI 10.17487/RFC6831, January
2013, <https://www.rfc-editor.org/info/rfc6831>.
[RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation
Protocol (LISP) Map-Server Interface", RFC 6833,
DOI 10.17487/RFC6833, January 2013,
<https://www.rfc-editor.org/info/rfc6833>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060,
February 2017, <https://www.rfc-editor.org/info/rfc8060>.
[RFC8111] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
Smirnov, "Locator/ID Separation Protocol Delegated
Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111,
May 2017, <https://www.rfc-editor.org/info/rfc8111>.
12.2. Informative References
[I-D.coras-lisp-re]
Coras, F., Cabellos-Aparicio, A., Domingo-Pascual, J.,
Maino, F., and D. Farinacci, "LISP Replication
Engineering", draft-coras-lisp-re-08 (work in progress),
November 2015.
[I-D.farinacci-lisp-mr-signaling]
Farinacci, D. and M. Napierala, "LISP Control-Plane
Multicast Signaling", draft-farinacci-lisp-mr-signaling-06
(work in progress), February 2015.
[I-D.ietf-lisp-eid-mobility]
Portoles-Comeras, M., Ashtaputre, V., Moreno, V., Maino,
F., and D. Farinacci, "LISP L2/L3 EID Mobility Using a
Unified Control Plane", draft-ietf-lisp-eid-mobility-01
(work in progress), November 2017.
[I-D.ietf-lisp-sec]
Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D.
Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-14
(work in progress), October 2017.
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[RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol
(LISP) Data-Plane Confidentiality", RFC 8061,
DOI 10.17487/RFC8061, February 2017,
<https://www.rfc-editor.org/info/rfc8061>.
Appendix A. Document Change Log
[RFC Editor: Please delete this section on publication as RFC.]
A.1. Changes to draft-ietf-lisp-signal-free-multicast-09
o Posted March 2018.
o Fixed idnits in draft.
A.2. Changes to draft-ietf-lisp-signal-free-multicast-08
o Posted February 2018.
o Fixed last call editorial comments.
A.3. Changes to draft-ietf-lisp-signal-free-multicast-07
o Posted November 2017.
o Changes after shepherd review and RFC1918 terminology compliant.
A.4. Changes to draft-ietf-lisp-signal-free-multicast-06
o Posted July 2017.
o Stig made a comment about referencing RFC6831 when an RLOC is a
multicast address. It opens up a lot of assumptions on what parts
of RFC6831 is performed and which parts should not be performed.
In the case of signal-free-multicast, join the underlay trees as a
multicast host by using IGMP.
A.5. Changes to draft-ietf-lisp-signal-free-multicast-05
o Posted July 2017.
o Make it clear that when a RLE is sent by an ETR and it is already
in the merged RLE list on the Map-Server, that the Map-Server
replaces the RLE entry (versus adding a duplicate RLE entry to the
list).
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o Make it clear that an RLOC can be a unicast or multicast address.
Then make a reference to RFC6831 about mechanisms to support
multicast RLOCs.
o Fix some typos.
A.6. Changes to draft-ietf-lisp-signal-free-multicast-04
o Posted May 2017.
o Make it clear that recieiver-ETRs need configuraiton information
for what Map-Servers (S,G) entries are registered to.
o Make it clear this document indicates what RTR layered hierarchy
to use and not if its the best hierarchy to use.
A.7. Changes to draft-ietf-lisp-signal-free-multicast-03
o Posted April 2017.
o Add "Multi-Homing Considerations" section to describe the case
where a source LISP site has multiple ITRs and the multicast
distribution tree at the source site branches to more than one
ITR. And at receiver sites where there are multiple ETRs and
multiple RLOCs per ETR.
A.8. Changes to draft-ietf-lisp-signal-free-multicast-02
o Posted October 2016.
o Updated document expiration timer.
A.9. Changes to draft-ietf-lisp-signal-free-multicast-01
o Posted April 2016.
o Add text to define RTRs and indicate how RTR level number is used
for LISP-RE.
o Draw figure 2 that shows a LISP-RE topology.
o Indicate that PIM-ASM or (*,G) trees can be supported in LISP
Signal-Free Multicast.
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A.10. Changes to draft-ietf-lisp-signal-free-multicast-00
o Posted late December 2015.
o Converted draft-farinacci-lisp-signal-free-multicast-04 into LISP
working group draft.
A.11. Changes to draft-farinacci-lisp-signal-free-multicast-04
o Posted early December 2015.
o Update references and document timer.
A.12. Changes to draft-farinacci-lisp-signal-free-multicast-03
o Posted June 2015.
o Update references and document timer.
A.13. Changes to draft-farinacci-lisp-signal-free-multicast-02
o Posted December 2014.
o Added section about how LISP-RE can use the mechanisms from
signal-free-multicast so we can avoid head-end replication and
avoid signalling across a layered RE topology.
A.14. Changes to draft-farinacci-lisp-signal-free-multicast-01
o Posted June 2014.
o Changes based on implementation experience of this draft.
A.15. Changes to draft-farinacci-lisp-signal-free-multicast-00
o Posted initial draft February 2014.
Authors' Addresses
Victor Moreno
Cisco Systems
170 Tasman Drive
San Jose, California 95134
USA
Email: vimoreno@cisco.com
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Dino Farinacci
lispers.net
San Jose, CA 95120
USA
Email: farinacci@gmail.com
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