Multicast | Mapping Agents

[zekebashi]

Hello,

I'm a bit confused with the configuration of the Auto-RP Mapping agents. I was analyzing our topology and found out that there are three L3 switches that are configured as mapping agents. My understanding is that there should be a single mapping-agent in the network for a specified group-list.

The mapping-agents are configured as follows:
    - On a core switches (C9509s configured in a VSS):

      interface loopback255

      ip address 10.1.255.254 255.255.255.255

      ip pim sparse-dense mode

     !

      ip pim autrp listener

      ip pim send-rp-announce lo255 scope 32 group-list Multicast interval 1

      ip pim-send-rp-discovery lo255 scope 32    ---- Defining mapping-agent

      ip pim accept-register list Mutltcast_Senders

      ip pim ssm default

    - Two distribution switches ( NX7Ks configured in a vPC domain):

     interface loopback99

     ip address 10.1.1.1 255.255.255.255

     ip pim sparse-mode

    !

    ip pim auto-rp rp-candidate lo99 group-list 224.0.0.0/4

     ip pim auto-rp mapping-agent lo99 (1.1.1.1/32 on NX7K_SWA and 1.1.1.2/32 on NX7K_SWB) --- Defining mapping agents

     ip pim auto-rp foward listenen

     ip pim ssm range 232.0.0.0/8

My question is how many mapping agents should be configured in a network? The above configs show three mapping-agents on three different switches.

https://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/ip-multicast/whitepaper_c11-508498.html

Thanks in advance, 

~zK

[Abzal]

Hi,

Generally speaking multiple RP mapping agents and RP candidates enhances the redundancy of the PIM-SM network. Being an RP or RP candidate doesn't add much CPU or memory overhead but plays an essential role for connecting sources with receivers in PM-SM network.

To your question -

It depends on many things like requirements of your network topology, high-availability and criticality etc.

To understand better show the output on all three devices:

sh ip pim rp
sh ip pim rp mapping