Boot Strap Router (BSR)

Note: BSR doesn't need this 224.0.1.39 and 224.0.0.14 because its uses unicast PIMv2.

Space inside the pimv2 it has info for RP and BSR.

Here R4 is the BSR and R2 and R3 are the candidate RP

Lets configure the BSR Router

R4(config)#ip pim bsr-candidate loopback 0

As soon as we configure the RP and BSR. PIMv2 packet has the info of who is the BSR and candidate RP

Lets look at the Packet details

Initially BSR doesn't know about the candidate RP therefore its just publishing the BSR info. As we configure the BSR on R4's loopback address.

Now configure the Candidate RP

R2(config)#ip pim rp-candidate loopback 0

R3(config)#ip pim rp-candidate loopback 0

BSR info got populated hop by hop hence R2 and R3 aware of BSR info. As soon as we configure the candidate RP it will send the unicast PIMv2 to R4 with the TTL 255.

BSR now advertise the know candidate RP info to all

This packet info explains clearly that R3 and R2 are the RP for group 224.0.0.0/4. But for the group 224.0.0.0/4 we have two RP which one it will take the is the question now?

To test this just send some multicast feed. Here the source is R7

R7#ping

Protocol [ip]:

Target IP address: 224.1.1.1

Repeat count [1]: 1000000000

Datagram size [100]:

Timeout in seconds [2]:

Extended commands [n]: yes

Interface [All]: loopback0

Time to live [255]:

Source address: 7.7.7.7

Type of service [0]:

Set DF bit in IP header? [no]:

Validate reply data? [no]:

Data pattern [0xABCD]:

Loose, Strict, Record, Timestamp, Verbose[none]:

Sweep range of sizes [n]:

Type escape sequence to abort.

Sending 1000000000, 100-byte ICMP Echos to 224.1.1.1, timeout is 2 seconds:

Packet sent with a source address of 7.7.7.7

...............................................

Lets check which RP knows about the group 224.1.1.1

R3#smr 224.1.1.1

Group 224.1.1.1 not found

R2#sh ip mroute 224.1.1.1 | b Int

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

(*, 224.1.1.1), 00:02:03/stopped, RP 2.2.2.2, flags: SP

  Incoming interface: Null, RPF nbr 0.0.0.0

  Outgoing interface list: Null

(7.7.7.7, 224.1.1.1), 00:02:03/00:02:57, flags: P

  Incoming interface: Serial1/0, RPF nbr 155.1.12.1

  Outgoing interface list: Null

R2#

As both the priority are same so the next tie breaker is lowest IP that’s is the reason its choosing the R2.

To test this more we will inc the priority of R2

R2(config)#ip pim rp-candidate loopback 0 priority 20

R2#sh ip mroute 224.1.1.1

Group 224.1.1.1 not found

R3#smr 224.1.1.1 | be In

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

(*, 224.1.1.1), 00:00:29/stopped, RP 3.3.3.3, flags: SP

  Incoming interface: Null, RPF nbr 0.0.0.0

  Outgoing interface list: Null

(7.7.7.7, 224.1.1.1), 00:00:29/00:02:30, flags: P

  Incoming interface: Serial1/0, RPF nbr 155.1.13.1

  Outgoing interface list: Null

So the lowest priority taking the precedence over higher.

RP selection process

Lowest priority>Lowest RP IP address