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What is Multicast Rendezvous Point (RP) ?

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By Edgar C Francis Internetworks

IP Multicast Routing

A Rendezvous Point (RP) is nothing but a router in a multicast network domain that acts as a shared root for a multicast shared tree. We can assign any number of routers and can be configured to work as Rendezvous Point RPs and they can be configured to cover different group ranges.














 




The reference point for the root of the shared tree

  • RP learns about the source using PIM register messages (RP pack with register stopped add (s.g).
  • RP learns about the destination using PIM join messages and Merge two trees together.
  • Joining the shortest path to the source and prune toward RP.
All the routers must agree on the conman RP

Here is the question that comes to mind. What if there is no RP?
  1. .       Source cannot register.
  2. .       Join cannot be processed.




Rendezvous point (static, auto RP, BSR)


Configuring  Rendezvous point.
  • Statically
  • Dynamically


1.       Auto-RP
2.       BSR

When you configure Static RP  we have to manually configure RP address on every router
All routers must have the same RP address. RP fail-over is not possible.

Auto RP
Auto-RP is a Legacy Cisco proprietary method of learning  RP information. all routers automatically learn RP address.

No configuration is necessary except on
  •  candidate RP (device willing to become RP).
  • mapping agent (choose the RP and relay this information to the rest of the PIM domain).
  • Permit backup RP’s to be configured.


How auto-RP works

1.       Candidate RP generates advertisements using ( s, 224.0.1.39) and groups with group information

2.       Mapping agent listen for (*. 224.0.1.39) to learn about RP mappings.
3.       Mapping agent generates an advertisement using (s.224.0.1.40) to distribute RP mapping information.
  • Every router must join 224.0.1.39 and 224.0.1.40 to learn information from the mapping  agent
  • By default using spare mode other routers can not join 224.0.1.40 (mapping agent)



Auto RP with multiple RP

  • Providers redundancy and load sharing.
  • An access list can be applied to control whatever RP server ever group.
  • If multiple RP-configured mapping agents select the best highest ip
  • Cannot use two RP same time for the same group.


Drawback of auto RP

Cisco proprietary.
Need to learn about 224.0.1.39/40
Not used in IPv6 multicast.

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