Multicast and MPLS-TE
Load mpls.te.multicast.init.cfg
The PE-CE links for XR13 and XR14 have been added to the global table. PIM is enabled everywhere with CSR9 as the RP. XR13 has joined group 239.1.1.1.
Currently XR14 can ping this group:
However, when the operator adds a bidircetional tunnel between CSR8 and XR11 with autoroute announce, multicast breaks. Add the bidirectional tunnel and explain the issue. Find a way to fix it.
Answer
Explanation
The problem is that the RPF check on XR11 fails when you add the TE tunnel. This is because the destination 10.8.14.14 is now via Tunnel-TE0 in the RIB. A TE tunnel never receives traffic, so multicast will always be broken for destinations that are via a TE tunnel. (Plus the TE tunnel does not have a valid PIM neighbor to use as the RPF neighbor).
We can verify this on XR11 with the following show command:
To fix this, we use the special command mpls traffic-eng multicast-intact under the IGP. This forces the router to use the IGP path as the RPF check, instead of using the TE route from the RIB. The addition of TE tunnels will not affect multicast’s SPF check.
Now XR11 has the RPF check as via the physical interface, even though the unicast route is still via the TE tunnel:
Traffic is working again:
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