Unanswered Question
Feb 28th, 2007

does anyone know a way around the problem with having an mroute pointing to a HSRP address and the PIM neigbour RPF failing as a result of PIM packets been sent from the Real address not the HSRP address. There is no option to implement and EGP or IGP.

The only workaround I can find is to set the mroute to the real IP address of the interface of the PIM neighbour but as a result we loose resilience of the mroute.

Any feedback appreciated.


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e-dennington Wed, 02/28/2007 - 07:42

The reason for this is that the HSRP VIP address is not a PIM neighbor and the join/prune messages are only sent between PIM neighbors, which would be the actual physical interface/vlan addresses. One way around this I have used in my environment is to manually join the interface/vlan in question to the specific multicast group addresse using ip igmp join-group x.x.x.x

kjbarrass Wed, 02/28/2007 - 07:47

Thankyou for the reply im afraid we cant add each group mannualy as we are a service provider with a large amount of clients connected and around 2000 multicast groups changing all the time. wasnt sure if VRRP offered anything more that might help this.

e-dennington Wed, 02/28/2007 - 08:01

Yeah, 2000 is alot to manually add! The other way around this that I know of is for the edge devices to have routes back to all PIM neighbors instead of a default route to a HSRP VIP (via ospf, eigrp etc). That way if a link or device goes down, you still have fault tolerance. Since you are a SP not sure how practical that is for you to do though.

kjbarrass Wed, 02/28/2007 - 08:13

Think we tried that and IOS will only allow 1 mroute statement per subnet and the solution we have is a vlan based one so if next hop died the route wouldnt drop from the routing table. Think I might have to just go the BGP route :0( thanks for feedback though. I tested VRRP it works to a point in that you can set one of the 2 routers to use standby address same as interfaces real address but when it fails over you end up with PIM hello's coming from wrong IP address.


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