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Group-to-RP Mapping

IETF Draft:

draft-joshi-pim-group-rp-mapping-01.txt

Authors:

Andy Kessler, Cisco Systems

Bharat Joshi, Infosys Technologies Ltd.

David McWalter, Data Connection Ltd

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Need for Standard Algorithm

Need for standard deterministic algorithm

No existing RFC/Draft defines a complete algorithm

A standard algorithm is required for interop

A standard algorithm could be used to determine the selected RP by a independent network management system

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Latest Revision

What's new in this rev ?

New use cases

Algorithm was tweaked for embedded RP

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Use Cases

Default static Group-to-RP mappings with dynamically learned entries

Default infrastructure for general purpose apps and specific mappings for special apps that change more often

Static Group-to-RP mappings with override-dynamic flag

Network Operators need to ability to nail down the RP mappings statically and ignore all dynamic messages

Migration situations

After acquisitions or mergers companies will need deterministic method to move from one RP mapping method to another (e.g. AutoRP to Bidir)

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Proposed Algorithm

The RP would be selected with this preference:

1. Embedded RP

2. Static with 'override-dynamic' flag

3. Longest match

4. PIM-Bidir over PIM-SM

5. Origin preference - bsr, auto-rp, static and other

6. Highest IP address

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Current Issues with Draft

Should we allow embedded RP for Bidir or specifically disallow it in the algorithm ?

Should Bidir be exempt from the BSR hashing algorithm ?

PIM-Bidir uses a group/mask entry to forward traffic to the RP. If we use the hash algorithm we will need to use a group/mask/hash entry which would be difficult to implement in hw

Should we remove the PIM hash function for all the RPs in Step 7 of the algorithm ?

Need to include text to not allow an RP for PIM-SSM groups

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References

Section 1.1 of RFC 5059 - BSR Mechanism for PIM

... the router chooses only one of the RPs by applying a deterministic algorithm so that all routers in the domain make the same choice. It is important to note that this algorithm is part of the specification of the individual routing protocols (and may differ among them), not of the BSR specification.

Section 3.3 of RFC 5059 - BSR Mechanism for PIM

If the BSR learns of both BIDIR and PIM-SM Candidate-RPs for the same group range, the BSR MUST only include RPs for one of the protocols in the BSMs. The default behavior SHOULD be to prefer BIDIR.

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References

Section 4.7.1 of RFC 4601 - PIM-SM Protocol Spec

Describes the existing algorithm for choosing a group from multiple Group-to-RP Mapping. It does not address these issues

– Does not consider the origin of a group-to-rp mapping (e.g. bsr, autorp, static, etc)

– Allow for static override

– Doesn't allow for higher priority of PIM-Bidir over PIM-SM

Section 4.7.2 of RFC 4601 - PIM-SM Protocol Spec

Describes the Hash function and talks about the highest IP address but only after the hash function.

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References

Section 7.1 of RFC 3956 - Embedded RP for IPv6

To avoid loops and inconsistencies, for addresses in the range FF70::/12, the Embedded-RP mapping MUST be considered the longest possible match and higher priority than any other mechanism.