12-15-2006 02:44 PM - edited 03-05-2019 01:21 PM
pls look at diagram attached.
Router A and B are branch routers. B is PIM DR on the LAN becuase it has higher IP 10.36.200.3. There is only sparse-mode running and RP is WAN2 across the WAN links.
1. Normally, multicast tree is built from router B to WAN2(RP)
2. But if link B goes down, router B must build tree from B, A, WAN1, core-rtr1 then WAN2
3. however would this ever work? because when link B goes down, router B is one-armed with only interface F1/0 connected. But I was told interface F1/0 can't be incoming and outgoing interfaces at the same time. As a result, the tree can never be set up.
is it true?
3. if true, does it mean this design is flawed for multicast?
4. remedy?
a backup link between router A and B via interface F1/1?
Thus router B can build tree via interface F1/1 which also becomes incoming int while F1/0 is outgoing interface
12-15-2006 06:13 PM
This design is perfectly valid even without the additional link between router A and B (F1/1 to F1/1).
If you loose link B, router B remains the DR and sends a PIM join towards router A as it receives the IGMP report message from the receiver. Router A puts F1/0 in the OIList for the specific group and therefore the receiver gets the multicast stream directly from Router A. As you stated router B doesn't put F1/0 in its OIList as this interface is also the incoming interface (rpf interface).
Hope this helps,
12-17-2006 07:43 AM
"router B doesn't put F1/0 in its OIList as this interface is also the incoming interface (rpf interface)"
1. does it imply router B would "refuse" to build the multicast tree or not?
2. in short, should this design work for multicast when link B goes down?
12-17-2006 04:53 PM
1. Router B doesn't need to build the mcast tree since it is not in the forwarding path. It simply needs to send the PIM join to router A when it gets the IGMP report message from the mcast listener (aka mcast receiver).
2. As I already stated, this design is perfectly valid even when link B goes down.
Hope this helps,
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