RPF check and default route

[sarahr202]

Hi everyone,

Hope all my friends are doing great.

This is what I see:

RP (200.200.200.2)--------200.200.200.20 PIM ROUTER--SOURCE ( 199.199.199.10)

RP has 0/0 pointed to 200.200.200.20

When RP receives a Register message ,and source IP of the stream is routed via 0.0.0.0 it results in RPF failure:

Mar 1 11:52:58.140: PIM(0): Received v2 Register on FastEthernet0/0 from 199.199.199.1
*Mar 1 11:52:58.140: for 199.199.199.10, group 235.1.1.1
*Mar 1 11:52:58.140: PIM(0): RPF lookup failed to source 199.199.199.10

When I pointed specific route 199.199.199.0/25 over a STATIC Route, I see RPF succeeds:

Below we can see RPF succeeds and ( S,G) state is created in multicast table:

ar 1 11:54:53.140: PIM(0): Received v2 Register on FastEthernet0/0 from 199.199.199.1
*Mar 1 11:54:53.140: for 199.199.199.10, group 235.1.1.1
*Mar 1 11:54:53.140: PIM(0): Forward decapsulated data packet for 235.1.1.1 on Loopback1
*Mar 1 11:54:53.216: PIM(0): Insert (199.199.199.10,235.1.1.1) join in nbr 200.200.200.20's queue
*Mar 1 11:54:53.216: PIM(0): Building Join/Prune packet for nbr 200.200.200.20
*Mar 1 11:54:53.216: PIM(0): Adding v2 (199.199.199.10/32, 235.1.1.1), S-bit Join

1)  From above, it appears simply having default route results in RPF failure, we need to have specific route for the source ip  in the table not just default route for RPF to succeeds

2) This is confusing:  My understand is RP does not perform RPF check on the  SRC IP of the encapsulated multicast stream in the Register message but we can see router is performing RPF check on the Register message pay load i,e SRC IP 199.199.199.10

Please share your thoughts and knowledge.

Have a nice day!!

[RAndrew · Accepted solution]

1) This is strange, I thought it should work with 0.0.0.0/0 too and I expect it should work (but never checked, tbh). What is `sh ip route 199.199.199.10` output without static route?

2) On first stage multicast goes via tunnel, on second stage via RP-spanning tree (RFP lookup) and on third via source spanning tree. So my thoughts about second question is read logs this way:

--- stage 1 log begins ---

*Mar 1 11:52:58.140: PIM(0): Received v2 Register on FastEthernet0/0 from 199.199.199.1
*Mar 1 11:52:58.140: for 199.199.199.10, group 235.1.1.1

--- stage 2 log begins ---

*Mar 1 11:52:58.140: PIM(0): RPF lookup failed to source 199.199.199.10

[sarahr202]

Here is what I missed:


1) Default route was not correctly configured, I have configured it as
0.0.0.0 255.255.255.255 rather than 0.0.0.0 0.0.0.0.
Once I fixed that, RPF check pass.

Thanks and have a nice weekend!!