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New Member

select anycast RP

Hello

Understand anycast RP selection is based on the unicast routes.

We have a typical two layer network. Two core routers are RPs, and the distributed routers have dual links to them. So the distributed routers will have equal routes to the virtual RP address. So which core router will they use? can we mannual force them?

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Bronze

Re: select anycast RP

By default, the router will automatically load share over, up to 4, equal cost paths. However this will be on a per session basis, rather than on a per packet, basis.

You can force the traffic to take a particular bath by changing the cost. Depending on what routing protocols you are running, you set the cost directly for OSPF or change the bandwidth/deley for EIGRP.

6 REPLIES
Bronze

Re: select anycast RP

By default, the router will automatically load share over, up to 4, equal cost paths. However this will be on a per session basis, rather than on a per packet, basis.

You can force the traffic to take a particular bath by changing the cost. Depending on what routing protocols you are running, you set the cost directly for OSPF or change the bandwidth/deley for EIGRP.

New Member

Re: select anycast RP

i'm assuming you are talking about multicast here, and multicast doesn't really load balance, so I have to disagree with previos post a little, with multicast, there is a rpf interface, if there are equal cost routes back to source, then I believe its one with highest ip address. This can be force with static mroute. i.e. I have 3 routers with multicast enabled, my source is behind router 1 and router 2 and 3 are attached, my vlans weren't numbered the same, so on one router, vlan 12 was rpf interface and on the other vlan 20 was rpf interface, this was actually causing a multicast loop. packet would come in on r1 and go out on all interfaces except source interface, then r2 would get packet and sent out on all vlans except 12, r3 would also get it and send out on all vlans except 20, (note r2 and r3 were also connected) then r2 would get the packets on all vlans except 20, therefore he received the packet on vlan12 again which was the rpf interface so he sent it out all non rpf interfaces. this occurred over and over on r2 and r3 until time to live decremented. solve problem by using static mroute on r2 and r3 and set rpf interface to be the same vlan, therefore when r2 receives the packet from r3, he receives it on only none rpf interfaces and drops the packet, eliminating the loop. If you wanted to load balance by groups you could assign multiple static mroutes alternating groups, note however that mroutes are considered in the order that they are entered kind of like access lists, therefore put more specific first and default last otherwise all will match default and there won't be any load balancing.

New Member

Re: select anycast RP

thanks for the information.

However i think in anycast RP, RP load balancing can be achieved by tuning unicast routes.

New Member

Re: select anycast RP

sorry, my answer was more for loadbalancing multicast traffic and had nothing to do with anycast rp

New Member

Re: select anycast RP

thanks. Your comment did explain multicast rpf clearly. regards

New Member

Re: select anycast RP

One more question to discuss.

We will configure RPs to be the two core switches. However there is one remote site using multicast also (might have both client and server). The wan link is 2M.

Shall I assign a local RP for this remote site and run MSDP on this router to the two core switches? or shall I just enable PIM on this remote site router?

I am afraid if there is no RP defined in this site, some of the local multicast traffics (esp the initial traffics) still need to go to the HQ RPs to reach the shared tree.

all suggestions are welcome

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