Using Cisco Auto-RP to learn RP address

Using Cisco Auto-RP to learn RP address

Stetson and Fedora routers are configured as C-RPs and Porkpie router is configured as the RP Mapping Agent. The scope parameter (sets the TTL value) indicates the number of hops the RP-Announce and RP-Discovery messages are allowed to travel.

When Fedora and Stetson routers are configured as C-RPs, they start to advertise RP-Announce messages to the RP Mapping Agent 10.224.1.3.

Fedora# debug ip pim auto-rp

*Mar 1 01:39:47.895: Auto-RP(0): Build RP-Announce for 10.224.1.2, PIMv2/v1, ttl 10, ht 181

*Mar 1 01:39:47.899: Auto-RP(0): Build announce entry for (239.0.0.0/8)

*Mar 1 01:39:47.903: Auto-RP(0): Send RP-Announce packet of length 48 on Serial0/0

*Mar 1 01:39:47.907: Auto-RP(0): Send RP-Announce packet of length 48 on Serial0/1

*Mar 1 01:39:47.911: Auto-RP(0): Send RP-Announce packet of length 48 on Serial0/2

*Mar 1 01:39:47.911: Auto-RP(0): Send RP-Announce packet of length 48 on Loopback0(*)

Porkpie is configured as the RP Mapping Agent, listens for RP-Announce messages and hence elects the RP for the group range advertised by the C-RPs. It also starts to send RP-Discovery messages advertising the single entry of group-to-RP mapping i.e. (239.0.0.0/8, 10.224.1.2) to 224.0.1.40 which all PIM enabled routers listen to. In this way, all PIM routers learn about the elected RP.

Porkpie# debug ip pim auto-rp

*Mar 1 01:38:27.551: Auto-RP(0): Build RP-Discovery packet

*Mar 1 01:38:27.555: Auto-RP: Build mapping (239.0.0.0/8, RP:10.224.1.2), PIMv2 v1,

*Mar 1 01:38:27.559: Auto-RP(0): Send RP-discovery packet of length 48 on FastEthernet0/0 (1 RP entries)

*Mar 1 01:38:27.563: Auto-RP(0): Send RP-discovery packet of length 48 on Serial0/0 (1 RP entries)

*Mar 1 01:38:27.567: Auto-RP(0): Send RP-discovery packet of length 48 on Serial0/1 (1 RP entries)

*Mar 1 01:38:27.571: Auto-RP(0): Send RP-discovery packet of length 48 on Loopback0(*) (1 RP entries)

The below output shows the RP Mapping Agent in use for a particular range of group in case of multiple RP Mapping Agents configured.

Porkpie# show ip pim rp mapping in-use

PIM Group-to-RP Mappings

This system is an RP-mapping agent (Loopback0)

Group(s) 239.0.0.0/8

RP 10.224.1.2 (?), v2v1

Info source: 10.224.1.2 (?), elected via Auto-RP

Uptime: 01:11:32, expires: 00:02:28

RP 10.224.1.1 (?), v2v1

Info source: 10.224.1.1 (?), via Auto-RP

Uptime: 01:07:44, expires: 00:02:16

Dynamic (Auto-RP or BSR) RPs in cache that are in use:

Group(s): 239.0.0.0/8, RP: 10.224.1.2, expires: 00:00:52

Porkpie# show ip pim rp

Group: 239.10.1.1, RP: 10.224.1.2, v2, v1, uptime 00:29:08, expires 00:02:54

Porkpie# show ip mroute

IP Multicast Routing Table

Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,

L - Local, P - Pruned, R - RP-bit set, F - Register flag,

T - SPT-bit set, J - Join SPT, M - MSDP created entry,

X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement,

U - URD, I - Received Source Specific Host Report,

Z - Multicast Tunnel, z - MDT-data group sender,

Y - Joined MDT-data group, y - Sending to MDT-data group

Outgoing interface flags: H - Hardware switched, A - Assert winner

Timers: Uptime/Expires

Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 239.10.1.1), 03:54:00/00:02:40, RP 10.224.1.2, flags: SP

Incoming interface: Serial0/0, RPF nbr 10.2.4.1

Outgoing interface list: Null

(*, 224.0.1.39), 03:53:07/stopped, RP 0.0.0.0, flags: DCL

Incoming interface: Null, RPF nbr 0.0.0.0

Outgoing interface list:

Loopback0, Forward/Sparse, 02:53:36/00:02:39

Serial0/1, Forward/Sparse, 02:55:17/00:00:00

Serial0/0, Forward/Sparse, 02:55:17/00:00:00

(10.224.1.1, 224.0.1.39), 02:56:05/00:02:37, flags: LT

Incoming interface: Serial0/1, RPF nbr 10.2.3.1

Outgoing interface list:

Loopback0, Forward/Sparse, 02:53:36/00:02:38

Serial0/0, Forward/Sparse, 02:55:17/00:00:00

(10.224.1.2, 224.0.1.39), 02:43:47/00:02:27, flags: LT

Incoming interface: Serial0/0, RPF nbr 10.2.4.1

Outgoing interface list:

Serial0/1, Forward/Sparse, 02:43:48/00:00:00

Loopback0, Forward/Sparse, 02:43:48/00:02:37

(*, 224.0.1.40), 03:54:12/stopped, RP 0.0.0.0, flags: DCL

Incoming interface: Null, RPF nbr 0.0.0.0

Outgoing interface list:

Loopback0, Forward/Sparse, 02:53:38/00:02:34

(10.224.1.3, 224.0.1.40), 02:53:37/00:02:48, flags: PLT

Incoming interface: Loopback0, RPF nbr 0.0.0.0

Outgoing interface list: Null

Using multiple RP Mapping Agents in a PIM domain:

Configuring multiple RP Mapping Agents in a PIM domain is good redundancy practice. However, each RP Mapping Agent functions independently. Their responsibility is to advertise Group-to-RP mapping periodically to all PIM routers in the domain.

As long as each RP Mapping Agent advertises same Group-to-RP mapping information, all routers in the domain still create only a single mapping cache entry.

The advantage of having multiple RP Mapping Agents is that it eliminates the need to maintain master-slave relationship and therefore the need for a failover protocol. If one RP Mapping Agent fails, other agents continue to work normally.