Use multicast routing to track frame-relay PVCs and route changes

[Phil Williamson]

I'm designing a frame-relay WAN. Core with fract DS3 and about 30 remote sites. I'll be using point-to-point sub-interfaces and EIGRP routing. Each remote will have a primary PVC with a CIR = half of port speed and a secondary PVC with zero-CIR. I can control the routing by using EIGRP bandwidth - zero-CIR sub-interface gets bandwidth less than primary sub-interface. However, I have heard that one can also use PIM to control the routing. How is this configured and better yet how/why does it work.

[leighharrison]

Hi there,

This works because EIGRP's update address is a multicast one - 224.0.0.10. PIM could be used to pass this around, but I would enter neighbour statements and put "ip igmp join-group" on loopbacks on the routers, so they are always listening.

You need to make sure that the Frame is aware of the multicast traffic, so it goes in the correct hardware queues

Regards,

LH

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[Richard Burts]

Leigh

I do not understand your comment about PIM passing around the EIGRP update address. 224.0.0.x are link local addresses and their traffic is not forwarded off the local segment.

I also do not understand the purpose of igmp join-group for this. If EIGRP is configured on the interface then the router will be listening for this multicast address anyway.

HTH

Rick

[leighharrison]

Hi there chaps,

I worte this pretty late last night and the more I think about it, you couldn't use pim to pass aroung eigrp updates - sorry for any confusion.

Regards,

LH

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[Phil Williamson]

Rick,

Maybe I heard incorrectly about using PIM in particular to control routing in my case. Since I have both a primary and secondary PVC and the primary has the much larger CIR then I need a way to prefer one over the other based on CIR/bandwith. Using the bandwidth metric is easy. Did I miss something with the multicast routing that would apply in my case? Now that I think about it I don't know how multicast routing will inject a route based on bandwidth???

Phil

[Richard Burts]

Phil

I do not believe that PIM would be able to do anything to achieve what you need. The good news is that there are several ways to do it within EIGRP. I will describe them in terms of what I would favor:

1) If one PVC does get larger bandwidth then EIGRP should prefer that link and use the other as backup. (be sure to check both ends to be sure that there is a bandwidth difference.)

2) change the delay on the interface of the 0 CIR to a larger value. In general I prefer changing delay to influence EIGRP metrics. But the interfaces should probably get a realistic bandwidth rather than the default, so that is why I listed bandwidth first.

3) configure an offset list to alter the EIGRP metric to make the 0 CIR less attractive.

HTH

Rick