Multicast-Auto-RP

Auto-RP was the first protocol to automatically distribute RP information across the
multicast domain.
Auto-RP defines two new concepts: Candidate RP (CRP) and Mapping Agents (MA).
CRP is any router that is willing to become an RP, sending UDP packets to the IP/Port
224.0.1.39/496, announcements are originated every 60 seconds by default

Mapping Agent(MA): Chooses RP among candidates and relay this information to PIM domain
The cRP announcements are flooded across the network and reach special routers
called Mapping Agents. Mapping Agents listen on the standard address 224.0.1.39 and collect all announcements from candidate RPs. After that, every mapping agent compiles a resulting list of Group to RP mappings and starts sending “RP discovery” messages to the special multicast address 224.0.1.40 port 496

Auto RP Listener
- dense for 224.0.1.39/224.0.1.40 only
- sparse for others 





R1(config)#ip pim send-rp-discovery lo0 scope 255
R1(config)#ip pim autorp listener

R2(config)#ip pim send-rp-announce lo0 scope 255
 









R2#
*Mar  1 00:57:09.167: Auto-RP(0): Received RP-discovery, from 1.1.1.1, RP_cnt 1, ht 181
*Mar  1 00:57:09.171: Auto-RP(0): Update (224.0.0.0/4, RP:2.2.2.2), PIMv2 v1
R2#
*Mar  1 00:57:17.743: Auto-RP(0): Build RP-Announce for 2.2.2.2, PIMv2/v1, ttl 255, ht 181
*Mar  1 00:57:17.743: Auto-RP(0):  Build announce entry for (224.0.0.0/4)
*Mar  1 00:57:17.747: Auto-RP(0): Send RP-Announce packet on FastEthernet0/0
*Mar  1 00:57:17.747: Auto-RP: Send RP-Announce packet on Loopback0