Internet DRAFT - draft-ietf-pim-ipv4-prefix-over-ipv6-nh
draft-ietf-pim-ipv4-prefix-over-ipv6-nh
Network Working Group A. Gupta
Internet-Draft Avi Networks
Intended status: Informational S. Venaas
Expires: November 2, 2018 Cisco Systems
May 1, 2018
Use of PIM Address List Hello across address families
draft-ietf-pim-ipv4-prefix-over-ipv6-nh-02.txt
Abstract
In the PIM Sparse Mode standard there is an Address List Hello option
used to list secondary addresses of an interface. Usually the
addresses would be of the same address family as the primary address.
In this document we provide a use case for listing secondary
addresses that are from a different family. In particular, Multi-
Protocol BGP (MP-BGP) has support for distributing next-hop
information for multiple address families using one AFI/SAFI Network
Layer Reachability Information (NLRI). When using this combined with
PIM, the Address List Hello option can be used to determine which PIM
neighbor to use as RPF neighbor.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Normative References . . . . . . . . . . . . . . . . . . 4
5.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The PIM Sparse Mode standard [RFC7761] defines an Address List Hello
option used to list secondary addresses of an interface. It
specifies that the addresses listed SHOULD be of the same address
family as the primary address. It was not anticipated that it could
be useful to list addresses of a different address family. This
document describes a use-case for listing different address families.
While use of MP-BGP along with [RFC5549] enables one routing protocol
session to exchange next-hop info for both IPv4 and IPv6 prefixes,
forwarding plane needs additional procedures to enable forwarding in
data-plane. For example, when a IPv4 prefix is learnt over IPv6
next-hop, forwarding plane resolves the MAC-Address (L2-Adjacency)
for IPv6 next-hop and uses it as destination-mac while doing inter-
subnet forwarding. While it's simple to find the required
information for unicast forwarding, multicast forwarding in same
scenario poses additional requirements.
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Multicast traffic is forwarding on a tree build by multicast routing
protocols such as PIM. Multicast routing protocols are address
family dependent and hence a system enabled with IPv4 and IPv6
multicast routing will have two PIM sessions one for each of the AF.
Also, Multicast routing protocol uses Unicast reachability
information to find unique Reverse Path Forwarding Neighbor. Further
it sends control messages such as PIM Join to form the tree. Now
when a PIMv4 session needs to initiate new multicast tree in event of
discovering new receiver It consults Unicast control plane to find
next-hop information. While this multicast tree can be Shared or
Shortest Path tree, PIMv4 will need a PIMv4 neighbor to send join.
However, the Unicast control plane can provide IPv6 next-hop as
explained earlier and hence we need certain procedures to find
corresponding PIMv4 neighbor address. This address is vital for
correct prorogation of join and furthermore to build multicast tree.
This document describes various approaches along with their use-cases
and pros-cons.
Figure 1: Example Topology
+-------------+ +-------------+
| | | |
| Router1 1::1/64 1::2/64 Router2 |
10.1.1.1/32--+ +--------I1---------| +-+PIM receiver
| 1.1.1.1/24 1.1.1.2/24 |
| + + |
| | | |
+-------------+ +-------------+
In example topology, Router1 and Router2 are PIMv4 and PIMv6
neighbors on Interface I1. Router2 learns prefix 10.1.1.1/32's next-
hop as 1::1/64 on Interface I1 as advertised by Router1 using BGP
IPV6 NLRI.But in order to send (10.1.1.1/32, multicast-group) PIMv4
join on Interface I1, Router2 needs to find corresponding PIMv4
neighbor. In case there are multiple PIMv4 neighbors on same
Interface I1, problem is aggravated.
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 BCP 14, [RFC2119].
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2. Solution
A PIM router can advertise its locally configured IPv6 addresses on
the interface in PIMv4 Hello messages as per [RFC7761] section 4.3.4.
Same applies for IPv4 address in PIMv6 Hello. PIM will keep this
info for each neighbor in Neighbor-cache along with DR-priority,
hold-time etc. Once IPv6 Next-hop is notified to PIMv4, it will look
into neighbors on the notified RPF-interface and find PIMv4 neighbor
advertising same IPv6 local address in secondary Neighbor-list. If
such a match is found, that particular neighbor will be uses as IPv4
RPF-Neighbor for initiating upstream join.
This method is valid for networks enabled with PIMv4 and PIMv6 both
as well for the networks enabled with only PIMv4 with IPv6 BGP
session or PIMv6 with IPv4 BGP session. This method does't required
any additional config changes in the network.
3. Security Considerations
There are no new security considerations.
4. IANA Considerations
There are no IANA considerations.
5. References
5.1. 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>.
5.2. Informative References
[RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
Layer Reachability Information with an IPv6 Next Hop",
RFC 5549, DOI 10.17487/RFC5549, May 2009,
<https://www.rfc-editor.org/info/rfc5549>.
[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>.
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Authors' Addresses
Ashutosh Gupta
Avi Networks
5155 Old Ironsides Dr. Suite 100
Santa Clara, CA 95054
USA
Email: ashutosh@avinetworks.com
Stig Venaas
Cisco Systems
821 Alder Drive
San Jose, CA 95035
USA
Email: stig@cisco.com
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