wdiff draft-ietf-mboned-msdp-deploy-00.txt draft-ietf-mboned-msdp-deploy-01.txt

MBONED Working GroupINTERNET-DRAFT Mike McBride
Internet Draft
draft-ietf-mboned-msdp-deploy-01.txt John Meylor
Cisco Systems
David Meyer
Sprint
Category Best Current Practice
Expires: November 2003 May 2003

Multicast Source Discovery Protocol (MSDP) Deployment Scenarios

<draft-ietf-mboned-msdp-deploy-00.txt>

1.
<draft-ietf-mboned-msdp-deploy-01.txt>

Status of this Memo Document

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. RFC2026.

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2. Abstract

This document describes best current practices for intra-domain is a product of an individual. Comments are solicited
and
inter-domain MSDP deployment.

3. should be addressed to the author(s).

4. Introduction

The

Abstract

This document describes best current practices for intra-domain and
inter-domain deployment of the Multicast Source Discovery Protocol [MSDP] is a mechanism to
connect multiple PIM-SM [RFC2117] domains together. Each PIM-SM
domain uses its own independent Rendezvous Point, or RP, and does not
have to depend on RPs
(MSDP) in other domains. Current best practice for
MSDP deployment utilizes conjunction with Protocol Independent Multicast (Sparse Mode)
and the Border Gateway Protocol With multi-protocol extensions
[RFC2858,NICKLESS]. This document outlines how these protocols work
together to provide Intra-domain and Inter-domain Any Source
multicast (ASM) service. In addition, this document describes how
MSDP can provide a PIM-SM domain with RP redundancy and load
balancing using the Anycast RP mechanism [ANYCAST-RP].

5. Sparse Mode
(PIM-SM).

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Inter-domain MSDP peering scenarios

The following sections describe the different inter-domain MSDP
peering possibilities and their deployment options.

5.1. scenarios. . . . . . . . . . . . . . 3
2.1. Peering between PIM border routers (Single hop peering)

In this case, the routers. . . . . . . . . . . . . 4
2.2. Peering between non border routers. . . . . . . . . . . . . 5
2.3. MSDP peers within the domain each have their own RP
located within a bounded PIM domain. In addition, peering without BGP. . . . . . . . . . . . . . . . . . 6
2.4. MSDP peering at a domain has it's
own Autonomous Number (AS) and BGP speakers. The domain may also have
multiple Multicast Exchange. . . . . . . . . . . . 7
3. Intra-domain MSDP speakers. Each router has an peering scenarios. . . . . . . . . . . . . . 7
3.1. Peering between MSDP and MBGP configured routers. . . . . . 7
3.2. MSDP peer is not BGP peering with
its peer routers. These deployments typically configure the (or no BGP
peering peer). . . . . . . . . 8
3.3. Hierarchical Mesh Groups. . . . . . . . . . . . . . . . . . 9
3.4. MSDP and Route Reflectors . . . . . . . . . . . . . . . . . 10
3.5. MSDP peering using the same directly connected next hop
peer IP address or another IP address from the same router. Typical
deployments of this type are providers who have a direct peering with
other providers or with providers who use their edge router to
MSDP/MBGP peer with customers.

For a direct peering inter-domain environment to be successful, the
first AS and Anycast RPs. . . . . . . . . . . . . . . . . . . . 11
4. Intellectual Property. . . . . . . . . . . . . . . . . . . . . 11
5. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations. . . . . . . . . . . . . . . . . . . . 12
6.1. Filtering SA messages . . . . . . . . . . . . . . . . . . . 12
6.2. SA message state limits . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References. . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References. . . . . . . . . . . . . . . . . . . 14
9. Author's Addresses . . . . . . . . . . . . . . . . . . . . . . 15
10. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 15

1. Introduction

MSDP [MSDP] is used primarily in the BGP best path to the originating RP must two deployment scenarios:

o Between PIM Domains

MSDP can be the same
as the AS of the used between Protocol Independent Multicast Sparse
Mode (PIM-SM) [RFC2362] domains to convey information
about active sources available in other domains. MSDP peer [MSDP]. As an example, consider the
following topology:

AS1----AS2----AS4
| /
| /
| /
AS3

In this case, AS4 receives an Source Active SA Message (SA),
originated by AS1 via AS2, which also has an BGP peering with AS4.
The BGP first hop AS from AS4,
used in the best path to the originating
RP, such cases is AS2. The origin AS of generally one to one peering, and
utilizes the sending MSDP peer is also AS2. The deterministic peer-RPF (Reverse Path Forwarding) check passes and the SA message is
forwarded.

A peer-RPF failure will occur
rules described in this topology when the BGP first-hop
AS MSDP specification (i.e., does not use
mesh-groups). Peerings can be aggregated on a single MSDP
peer. Such a peer can typically have from one to hundreds of
peerings, which is similar in the best path scale to the originating RP BGP peerings.

o Within a PIM Domain

MSDP is AS2 while often used between Anycast Rendezvous Points
(Anycast-RPs) [RFC3446] within a PIM domain to synchronize
information about the origin AS active sources being served by each
Anycast-RP peer (by virtue of the sending MSDP peer is AS3. An IGP reachability). MSDP peering between AS2 and AS4
would prevent
used in this failure from occurring.

5.2. Peering between non border routers (Multi-hop peering)

While the eBGP peer scenario is typically directly connected between border
routers, it based on MSDP mesh groups,
where anywhere from two to tens of peers can comprise a given
mesh group, although more than ten is common not typical. One or more
of these mesh-group peers may then also have additional
one-to-one peering with MSDP peers outside that PIM domain for the
discovery of external sources. MSDP peer to be located deeper into the
transit providers AS. However, for anycast-RP without
external MSDP scalability peering is sacrificed if a
provider must maintain BGP valid deployment option and common.

Current best practice for MSDP peerings deployment utilizes PIM-SM and the
Border Gateway Protocol with all their edge
routers so that they can BGP multi-protocol extensions (MBGP)
[RFC1771, RFC2858]. This document outlines how these protocols work
together to provide an intra-domain and inter-domain Any Source
Multicast (ASM) service.

2. Inter-domain MSDP peer with customer routers.
Alternatively, providers commonly choose a few dedicated routers
within their core network for peering scenarios

The following sections describe the most common inter-domain MSDP peerings to
peering possibilities and their
customers. These core MSDP deployment options.

2.1. Peering between PIM border routers will also typically be in

In this case, the
providers intra-domain MSDP mesh [MSDP] group and configured for
Anycast RP. All multicast routers in the providers AS should
statically point to peers within the Anycast RP address. AutoRP and BSR mechanisms
could be used to disseminate domain have their own RP information
located within the provider's
network.

For an SA message to be accepted in this (multi-hop peering)
environment, the a bounded PIM domain. In addition, a domain has it's
own Autonomous System (AS) number MBGP speakers. The domain may also
have multiple MSDP peer address must be in the same AS as the AS
of the speakers. Each border router has an MSDP and MBGP
peering with its peer and must be advertised via MBGP. For example, using routers. These external MSDP peering
deployments typically configure the diagram below, if customer R1 router is MBGP peering with AS2
provider's R2 router and if R1 is MSDP peering with R3 router, then
R2 and R3 must be in
using the same AS. R1 also must have the MSDP directly connected next hop peer IP address or other
IP address from the same router. Typical deployments of R3 in its BGP table.

+--+ +--+ +--+
|R1|----|R2|----|R3|
+--+ +--+ +--+
AS1 AS2 AS2

5.3. MSDP peering without BGP

In this case, an enterprise maintains its own RP and has an MSDP type are
providers who have a direct peering with other providers, providers
peering at an exchange, or providers who use their service provider, but does not BGP edge router to
MSDP/MBGP peer with them.
MSDP relies upon BGP path information customers.

For a direct peering inter-domain environment to learn be successful, the MSDP topology for
first AS in the SA peer-RPF check. MSDP can MBGP best path to the originating RP should be deployed without BGP, however, and the
same as a result there are some special cases where the requirement to
perform AS of the MSDP peer. As an peer-RPF check on example, consider the BGP path information is suspended.
following topology:

AS1----AS2----AS4
| /
| /
| /
AS3

In this case (when there is only a single MSDP peer connection) a
default peer (default MSDP route) is configured and either the
originating RP is directly connected or case, AS4 receives a mesh group is used. An
enterprise will Source Active (SA) message, originated
by AS1, from AS2. AS2 also typically configure a unicast default route has an MBGP peering with AS4. The MBGP
first hop AS from
their border router AS4, in the best path to the provider's border router and then MSDP
peer with originating RP, is
AS2. The origin AS of the provider's border router. If internal sending MSDP peerings are peer is also used within AS2. In this
case, the enterprise, then an peer-Reverse Path Forwarding check (peer-RPF check) passes
and the SA message is forwarded.

A peer-RPF failure would occur in this topology when the MBGP first
hop AS, in the best path to the originating RP, is AS2 while the
origin AS of the sending MSDP default peer will need
to be configured on is AS3. This reliance upon BGP AS
PATH information prevents endless looping of SA packets.

Router code, which has adopted the border router pointing to latest rules in the provider. In
this way, all external multicast sources MSDP draft,
will be learned and internal
sources can be advertised.

5.4. relax the rules Between AS's a bit. In the following topology we
have an MSDP peering between mesh groups

Mesh groups which are within different PIM domains can MSDP peer with
one another AS1<->AS3 and AS3<->AS4:

RP
AS1----AS2----AS3----AS4
If the first AS in best path to exchange information about active sources. An the RP
within AS1's mesh group may does not equal the MSDP peer,
MSDP peer RPF fails. So AS1 cannot MSDP peer with an RP which AS3 since AS2 is within
AS2's mesh group. However, there should be no mesh group
the first AS in common
between PIM domains. It is important the MBGP best path to note however, that mesh
groups that span PIM domains is not recommended, as SA forwarding
loops can develop. As an example, consider AS4 RP. With the following topology:

AS2
/ \
/ \
/ \
/ \
/ \
AS1 -------- AS3
If each AS had their own intra-domain MSDP mesh group, and if there
was an inter-domain latest MSDP mesh group between AS1-AS2, AS1-AS3, and
AS2-AS3 then an SA loop would be created. Since there is no RPF check
between mesh groups,
draft compliant code, AS 1 will choose the SAs would loop around from one PIM domain to
another.

5.5. MSDP peering at a Multicast Exchange

Multicast exchanges allow multicast providers to peer at a common IP
subnet and share MSDP SA updates. Each provider in the closest AS
along best AS path to the RP. AS1 will then accept SA's coming from
AS3. If there are multiple MSDP and BGP peers to routers within the same AS,
the peer with each others directly connected exchange the highest IP address. Each
exchange router will send/receive SAs over address is chosen as the exchange fabric. They
will then be able to forward SAs throughout their domain to their
customers and any direct provider peerings.

6. Intra-domain RPF peer.

2.2. Peering between non border routers

When MSDP peering scenarios

The following sections describe the different between border routers, intra-domain MSDP
peering possibilities
scalability is restricted because it is necessary to also maintain
MBGP and their deployment options.

6.1. Peering between routers configured for both MSDP and MBGP

The next hop IP address of peerings internally towards their border routers.
Within the iBGP peer (that is MSDP is advertising
as intra-domain, the border router becomes the announcer of
the next hop toward towards the originating RP) is used for the peer-RPF
check. RP. This is different from requires that all
intra-domain MSDP peerings must mirror the inter-domain BGP/MSDP case, where MBGP path back towards the
border router. External MSDP (eMSDP) peerings rely upon AS path information is used for
peer rpf checking, while internal MSDP (iMSDP) peerings rely upon the peer-RPF check. For this reason,
announcer of the next hop.

While the eMBGP peer is typically directly connected between border
routers, it is necessary common for the IP address of the MSDP eMSDP peer connection to be located deeper into
the same as the internal BGP peer connection whether or not transit providers AS. Providers, which desire more flexibility in
MSDP peering placement, commonly choose a few dedicated routers
within their core network for the
MSDP/MBGP peers are directly connected. A successful deployment would
be similar inter-domain MSDP peerings to their
customers. These core MSDP routers will also typically be in the following:

+----+
| Rb | 3.3.3.3
/ +----+
AS1 AS2 / |
+---+ +--+ / |
|RP1|---------|Ra| |
+---+ +--+ |
1.1.1.1 2.2.2.2 |
\ |
\ |
\ +-----+
| RP2 |
+-----+

Where RP2
providers intra-domain MSDP mesh group and MBGP peers with Ra using 2.2.2.2 and with Rb using
3.3.3.3. When configured for Anycast RP.
All multicast routers in the MSDP SA update arrives on RP2 from Ra, providers AS should statically point to
the MSDP RPF
check Anycast RP address. Static RP assignment is the most commonly
used method for 1.1.1.1 passes because RP2 receives group to RP mapping due to its deterministic nature.
Auto-RP [AUTORP] and/or the Bootstrap Router (BSR) [BSR] dynamic RP
mapping mechanisms could be also used to disseminate RP information
within the provider's network

For an SA update from
2.2.2.2 which is message to be accepted in this (multi-hop peering)
environment, we rely upon the correct BGP next hop (or closest, with latest MSDP
spec) AS in the best path towards originating RP for 1.1.1.1.

When RP2 receives the same SA update from rpf check.
The MSDP peer 3.3.3.3, address should be in the BGP
lookup for 1.1.1.1 shows a next hop same AS as the AS of 2.2.2.2 so RPF correctly
fails, preventing a loop.

This deployment would the
border routers MBGP peer. The MSDP peer address should be advertised
via MBGP.

For example, using the diagram below, if customer R1 router is MBGP
peering with R2 router and if R1 is MSDP peering with R3 router, then
R2 and R3 must be in the same AS. The MSDP peer with the highest IP
address will be chosen as the MSDP RPF peer. R1 must also fail have the
MSDP peer address of R3 in its MBGP table.

+--+ +--+ +--+
|R1|----|R2|----|R3|
+--+ +--+ +--+
AS1 AS2 AS2

From R3's perspective, AS1 (R1) is the MBGP next AS in the best path
towards the originating RP. As long as AS1 is the next AS (or
closest) in the best path towards the originating RP, RPF will
succeed on an update SAs arriving from Ra to RP2 if RP2
was BGP R1.

In contrast, with the single hop scenario, with R2 (instead of R3)
border MSDP peering with R1 border, R2s MBGP address becomes the
announcer of the next hop for R3, towards the originating RP, and R3
must peer with that R2 address. And all AS2 intra-domain MSDP peers
need to an follow iMBGP (or other IGP) peerings towards R2 since iMSDP
has a dependence upon peering with the address of the MBGP (or other than 2.2.2.2 on Ra. Intra-domain
deployments should have
IGP) announcer of the next hop.

2.3. MSDP and MBGP peering addresses which match.

6.2. without BGP

In this case, an enterprise maintains its own RP and has an MSDP peer is
peering with their service provider, but does not BGP peer (or no BGP peer)

This is a common with them.
MSDP intra-domain deployment in environments where
few routers are running relies upon BGP or where path information to learn the MSDP topology for
the SA peer-RPF check. MSDP can be deployed without BGP, however, and
as a result there are some special cases where the requirement to
perform an peer-RPF check on the BGP path information is suspended.
These cases are when there is only a single MSDP peer connection, a
default peer (default MSDP route) is configured, the originating RP
is directly connected, a mesh group is used, or an implementation is
is used which allows for an MSDP peer RPF check using an IGP.

An enterprise will typically configure a unicast default route from
their border router to the provider's border router and then MSDP
peer with the provider's MSDP router. If internal MSDP peerings are
also used within the enterprise, then an MSDP default peer will need
to be configured on the border router pointing to the provider. In
this way, all external multicast sources will be learned and internal
sources can be advertised. If only a single MSDP peering was used (no
internal MSDP peerings) towards the provider, then this stub site
will MSDP default peer towards the provider and skip the BGP RPF
check.

2.4. MSDP peering at a Multicast Exchange

Multicast exchanges allow multicast providers to peer at a common IP
subnet (or by using point to point virtual LANs) and share MSDP SA
updates. Each provider will MSDP and MBGP peer with each others
directly connected exchange IP address. Each exchange router will
send/receive SAs to/from their MSDP peers. They will then be able to
forward SAs throughout their domain to their customers and any direct
provider peerings.

3. Intra-domain MSDP peering scenarios

The following sections describe the different intra-domain MSDP
peering possibilities and their deployment options.

3.1. Peering between MSDP and MBGP configured routers

The next hop IP address of the iBGP peer is typically used for the
MSDP peer-RPF check (IGP can also be used). This is different from
the inter-domain BGP/MSDP case, where AS path information is used for
the peer-RPF check. For this reason, it is necessary for the IP
address of the MSDP peer connection be the same as the internal MBGP
peer connection whether or not the MSDP/MBGP peers are directly
connected. A successful deployment would be similar to the following:

+----+
| Rb | 3.3.3.3
/ +----+
AS1 AS2 / |
+---+ +--+ / |
|RP1|---------|Ra| |
+---+ +--+ |
1.1.1.1 2.2.2.2 |
\ |
\ |
\ +-----+
| RP2 |
+-----+
Where RP2 MSDP and MBGP peers with Ra (using 2.2.2.2) and with Rb
(using 3.3.3.3). When the MSDP SA update arrives on RP2 from Ra, the
MSDP RPF check for 1.1.1.1 passes because RP2 receives the SA update
from MSDP peer 2.2.2.2 which is also the correct MBGP next hop for
1.1.1.1.

When RP2 receives the same SA update from MSDP peer 3.3.3.3, the MBGP
lookup for 1.1.1.1 shows a next hop of 2.2.2.2 so RPF correctly
fails, preventing a loop.

was MBGP peering to an address other than 2.2.2.2 on
Ra. Intra-domain deployments must have MSDP and MBGP (or other
IGP) peering addresses which match, unless a method to skip the
peer rpf check is deployed.

3.2. MSDP peer is not BGP peer (or no BGP peer)

This is a common MSDP intra-domain deployment in environments where
few routers are running MBGP or where the domain is not running MBGP.
The problem here is that the MSDP peer address needs to be the same
as the MBGP peer address. To get around this requirement, the intra-
domain MSDP RPF rules have been relaxed in the following topologies:

o By configuring the MSDP peer as a mesh group peer

o By having the MSDP peer be the only MSDP peer

o By configuring a default MSDP peer

o By peering with the originating RP.

o By relying upon an IGP for MSDP peer RPF

The common choice around the intra-domain BGP peering requirement,
when more than one MSDP peer is configured, is to deploy MSDP mesh
groups. When a MSDP mesh group is deployed, there is no RPF check on
arriving SA messages when received from a mesh group peer.
Subsequently, SA messages are always accepted from mesh group peers.
MSDP mesh groups were developed to reduce the amount of SA traffic in
the network since SAs, which arrive from a mesh group peer, are not
flooded to peers within that same mesh group. Mesh groups must be
fully meshed.

If recent (but not currently widely deployed) router code is running
which is fully complaint with the latest MSDP draft, another option,
to work around not having BGP to MSDP RPF peer, is to RPF using an
IGP like OSPF, IS-IS, RIP, etc. This new capability will allow for
Enterprise customers, who are not running BGP and who don't want to
run mesh groups, to use their existing IGP to satisfy the MSDP peer
RPF rules.

3.3. Hierarchical Mesh Groups

Hierarchal Mesh Groups are occasionally deployed in intra-domain
environments where there are a large number of MSDP peers. Allowing
multiple mesh groups to forward to one another can reduce the number
of MSDP peerings per router (due to the full mesh requirement) and
hence reduce router load. A good hierarchical mesh group
implementation (one which prevents looping) contains a core mesh
group in the backbone and these core routers serve as mesh group
aggregation routers:

[R2]{A,2}
/ \
/ \
/ \
/ \
/ \
/ \
/ \
{A,1}[R1]-------------[R3]{A,3}

In this example, R1, R2, R3 are in MSDP mesh group A (the core mesh
group) and each serves as MSDP aggregation routers for their leaf (or
second tier) mesh groups 1, 2, and 3. Since SA messages received from
a mesh group peer are not forwarded to peers within that same mesh
group, SA messages will not loop. Do not create topologies which
connect mesh-groups in a loop. In the above example for instance,
second tier mesh-groups 1, 2, and 3 must not directly exchange SA
messages with each other or an endless SA loop will occur.

Redundancy, between mesh groups, will also cause a loop and is
subsequently not available with Hierarchical mesh groups. For
instance, assume R3 had two routers connecting it's leaf mesh group 3
with the core mesh group A. A loop would be created between mesh
group 3 and mesh group A because each mesh group must be fully meshed
between peers.

3.4. MSDP and Route Reflectors

or confederation members, be fully meshed to prevent loops. In
the route reflector environment, MSDP requires that the route
reflector clients peer with the route reflector since the RR is
the BGP announcer of the next hop towards the domain is not running BGP. originating
RP. The problem here RR is that not the MSDP peer address needs to be BGP next hop, but is the same
as announcer of the
BGP peer address. To get around this requirement, next hop. The announcer of the intra-
domain next hop is the address
typically used for MSDP peer RPF rules have been relaxed in certain as follows:

o By configuring checks. For example, consider
the following case:

Ra--------RR
/|\
/ | \
A B C

Ra is forwarding MSDP peer as a mesh group peer,
o By having SAs to the route reflector RR. Routers A, B,
and C also MSDP peer be with RR. When RR forwards the only MSDP peer,
o By configuring a default SA to A, B, and C,
these RR clients will accept the SA because RR is the announcer of
the next hop to the originating RP address.

An SA will peer-RPF fail, if Ra MSDP peer, or
o By peering peers directly with Routers A,
B, or C, because the originating RP.

The common choice around announcer of the intra-domain BGP peering requirement,
when more than one MSDP peer next hop is configured, RR, but the SA
update came from Ra. Proper deployment is to deploy have RR clients MSDP mesh
groups. When a
peer with the RR. MSDP mesh group is deployed, there groups may be used to work around this
requirement. External MSDP peerings will also prevent this
requirement since the next AS is no RPF check on
arriving SA messages when received from a mesh group peer.
Subsequently, SA messages are always accepted from mesh group peers. compared between MBGP and MSDP
peerings, rather than the IP address of the announcer of the next
hop.

Some recent MSDP implementations conform to the latest MSDP mesh groups are helpful in reducing draft
which relaxes the amount requirement of SA traffic peering with the Advertiser of the
Next Hop (the Route Reflector). This new rule allows for peering with
the Next-Hop, in addition to the network since SAs are not flooded Advertiser of the next hop. In the
example above, for instance, if Ra is the Next-Hop (perhaps due to other mesh group peers.

7.
using BGP's Next hop self attribute) and if routers A,B,C are peering
with Ra, the SA's received from Ra will now succeed.

3.5. MSDP and Anycast RPs

A network network, with multiple RPs, can achieve RP load sharing and
redundancy by using the Anycast RP mechanism in conjunction with MSDP
mesh groups
[ANYCAST-RP]. [RFC3446]. This mechanism is a common deployment
technique used within a domain by service providers, who commonly providers and Enterprises
which deploy several RPs within their domain. These RPs will all each
have the same IP address configured on a Loopback interface (making
this the anycast addresses). Anycast address). These RPs will MSDP peer with each other
using a separate loopback interface and are part of the same fully
meshed MSDP mesh group. This second Loopback
interface loopback interface, used for MSDP
peering, will typically also be used for the MBGP peering. All
routers within the provider's domain will learn of the Anycast RP
address either through AutoRP, Auto-RP, BSR, or a static RP assignment. Each
designated router in the domain will send source registers and group
joins to the Anycast RP address. Unicast routing will direct those
registers and joins to the nearest Anycast RP. If a particular
Anycast RP router fails, unicast routing will direct subsequent
registers and joins to the nearest Anycast RP. That RP will then
forward an MSDP update to all peers within the global MSDP mesh
group. Each RP will then forward (or receive) the SAs to (from)
external customers and providers.

7.1. Hierarchical Mesh Groups

Hierarchial Mesh Groups are typically deployed in intra-domain
environments where there are a large number of MSDP peers. Allowing
multiple mesh groups to forward to one another can reduce the number
of MSDP peerings per router and hence reduce router load. A good
hierarchical mesh group implementation (one which prevents looping)
contains a core mesh group in the backbone and these core routers
serve as mesh group aggregation routers:

[R2]{A,2}
/ \
/ \
/ \
/ \
/ \
/ \
/ \
{A,1}[R1]-------------[R3]{A,3}
In this example, R1, R2, R3 are in MSDP mesh group A (the core mesh
group) and each serves as MSDP aggregation routers for their mesh
groups 1, 2, and 3. Since SA messages received from a mesh group peer
are not forwarded to peers within that same mesh group, SA messages
will not loop. In particular, do not create topologies which connect
mesh-groups in a loop. In within the above example for instance, "second
tier" mesh-groups 1, 2, and 3 must not directly exchange SA message.

7.2. Anycast MSDP mesh
group. Each RP will then forward (or receive) the SAs to (from)
external customers and Route Reflectors

BGP requires all iBGP speakers that are not route-reflector clients providers.

4. Intellectual Property

The IETF takes no position regarding the validity or confederation members scope of any
intellectual property or other rights that might be fully meshed. This requirement does not
scale when there are large number claimed to
pertain to the implementation or use of iBGP speakers. In the route-
reflector environment, MSDP requires technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the route reflector clients
peer
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the route reflector. For example, consider result of an attempt made to
obtain a general license or permission for the following
case:

Ra--------RR
/|\
/ | \
A B C

Ra is forwarding MSDP SAs use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the route reflector RR. Routers A, B,
and C also MSDP peer with RR. When RR forwards information to the SA IETF Executive
Director.

5. Acknowledgments

The authors would like to A, B, thank John Zwiebel and C,
these RR clients will accept Swapna Yelamanchi
for their feedback on earlier versions of this document.

6. Security Considerations

An MSDP service should be secured by explicitly controlling the SA because RR state
which is created by, and passed within, the iBGP next hop
for the originating RP address.

An SA will peer-RPF fail if Ra MSDP peers directly service. As with Routers A, B,
unicast routing state, MSDP state should be controlled locally, at
the edge origination points. Selective filtering at the multicast
service edge helps ensure that only intended sources result in sa-
message creation, and C because this control helps to reduce the iBGP next hop for RR's clients is RR, but likelihood of
state-aggregation related problems in the SA
update came from Ra. Proper deployment is core. There are a variety
of points where local policy should be applied to have RR's clients MSDP
peer with RR.

7.3. the MSDP service.

6.1. Filtering SA messages

The process of originating sa-messages should be filtered to ensure
only intended local sources are resulting in sa-message origination.
In addition, MSDP speakers should filter on which sa-messages get
received and forwarded.

Typically there is a fair amount of (S,G) state in a PIM-SM domain
that is local to the domain. However, without proper filtering, SA- sa-
messages containing these local (S,G) announcements may be advertised
to the global MSDP infrastructure. Examples of this includes domain
local applications that use global IP multicast addresses and sources
that use RFC 1918 addresses [RFC1918]. To improve on the scalability
of MSDP and to avoid global visibility of domain local (S,G)
information, the following external SA filter list is recommended to
help prevent unnecessary creation, forwarding, and caching of some of
these well-known �domain local� sources [IANA]. domain local sources.

224.0.0.0/4 Local Specific local application packets
(packets from any application which are intended to stay
adminstratively scoped, but use global addressing. The
current list of applications which could be filtered
is dynamic and subject to individual policy. See WG
mail group for latest recommendations) [IANA]
224.0.1.39 AutoRP Auto-RP Announce [AUTORP]
224.0.1.40 AutoRP Auto-RP Discovery [AUTORP]
239.0.0.0/8 Admin. Administratively Scoped IP Multicast [RFC2365]
10.0.0.0/8 private Private addresses [RFC1918]
127.0.0.0/8 private Private addresses [RFC1918]
172.16.0.0/12 private Private addresses [RFC1918]
192.168.0.0/16 private Private addresses [RFC1918]
232.0.0.0/8 Default SSM-range

8. Author's Addresses

Mike McBride
Cisco Systems
mcbride@cisco.com

John Meylor
Cisco Systems
jmeylor@cisco.com

David Meyer
Sprint
Email: dmm@sprint.net

9. REFERENCES

[ANYCAST-RP] D. Meyer et. al, "Anycast RP mechanism using PIM [SSM]

6.2. SA message state limits

Proper filtering on sa-message origination, receipt, and
MSDP", draft-ietf-mboned-anycast-rp-08.txt, May, 2001.

[NICKLESS] Bill Nickless, "IPv4 Multicast Best Current Practice",
draft-nickless-ipv4-mcast-bcp-01.txt, February 2002.

[IANA] http://www.iana.org forwarding
will significantly reduce the likelihood of unintended and unexpected
spikes in MSDP state However, a sa-cache state limit SHOULD BE be
configured as a final safeguard to state spikes.

7. IANA Considerations

This document creates a no new requirements on IANA namespaces
[RFC2434].

8. References

8.1. Normative References

[MSDP] Meyer, D. Meyer and Bill W. Fenner (Editors), "The Multicast
Source Discovery Protocol (MSDP)", draft-ietf-msdp-spec-13.txt,
November 2001. draft-ietf-msdp-spec-19.txt,
May 2003. Work in Progress.

[SSM] Holbrook, H., and B. Cain, "Source-Specific
Multicast for IP", draft-ietf-ssm-arch-03.txt,
May, 2003. Work in Progress.

[RFC1771] Rekhter, Y., and T. Li, "A Border Gateway
Protocol 4 (BGP-4)", RFC 1771, March 1995.

[RFC1918] Y. Rekhter, R. Moskowitz, D. Karrenberg, G. de
Groot, E. Lear, "Address Allocation for Private
Internets", 02/29/1996.

[RFC2117] D. Estrin et. al, "Protocol Independent Multicast-Sparse
Mode (PIM-SM): Protocol Specification", RFC 2117,
June, 1997. 1918, Feburary, 1996.

[RFC2362] D. Estrin, et. al., "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol
Specification", RFC 2362, June, 1998.

[RFC2365] Meyer, D. "Administratively Scoped IP Multicast",
RFC 2365, July, 1998.

[RFC2434] Narten, T., and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in
RFCs", RFC 2434/BCP 0026, October, 1998.

[RFC2858] T. Bates, Bates T., Y. Rekhter, R. Chandra, D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 2858,
June 2000.

[RFC3446] Kim, D., et. al., "Anycast Rendezvous Point (RP)
Mechanism using Protocol Independent Multicast
(PIM) and Multicast Source Discovery Protocol
(MSDP)", RFC 3446, January, 2003.

8.2. Informative References

[AUTORP] Fenner, W., et. al., " Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol
Specification (Revised)", draft-ietf-pim-sm-v2-new-07.txt,
March, 2003. Work in Progress.

[BSR] Fenner, W., et. al., "Bootstrap Router (BSR)
Mechanism for PIM Sparse Mode", draft-ietf-pim-sm-bsr-03.txt,
February, 2003. Work in Progress.

[IANA] http://www.iana.org

9. Author's Addresses

Mike McBride
Isac Systems
Email: mcbride@cisco.com

John Meylor
Cisco Systems
Email: jmeylor@cisco.com

David Meyer
Email: dmm@maoz.com

10. Full Copyright Statement

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and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
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ing
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