![]() Essentially we tell router2 to act by the following rules… By doing that, we’re telling router2 to sort of change the traditional rules of iBGP advertisements. We made router2 a route reflector just by telling it that it’s peers were route reflector clients. You saw above the configuration isn’t all that involved. So let’s talk about what a route reflector actually does. We see that router3 now has all of the loopbacks. Now let’s see what we have on router3 which previously has 3 out of the 5 loopbacks… Once the configuration goes in you should see the sessions bounce and reset… Let’s configure router2 as a route reflector to start with… This is where we can use route reflectors to save ourselves some pain and agony. Peering each of the routers together would mean that I’d have to configure 12 more BGP sessions. At this point, router2 has the most visibility of the network with 4 out of the 5 router loopbacks in it’s BGP table (it’s own and one for each BGP peer that it has). Given this topology, and assuming that all of the routers are in AS 100, let’s peer each of the directly connected routers and see what we get…Īs expected, each router did NOT forward any of the iBGP updates it heard to any of the other routers. I think the concept is best explained with an example so let’s just jump right into a topology… One of the ways to get around this restriction is to use route reflectors. Bottom line is that iBGP speakers will not forward iBGP learned routes to other iBGP peers.Īs you can imagine, in some designs, peering every router to every other router in the same AS could be quite the task. Since iBGP updates are sent within a single AS, the AS-path attribute isn’t updated and if iBGP speakers continued to forward updates, we would have routing loops. ![]() A BGP speaker will drop any update it receives that has it’s own AS listed in the AS-Path attribute. You’ll recall the BGP uses the AS-Path attribute to prevent against loops. The purpose of this is namely to fix any issues around loop prevention. That is, each router is peered to every other router within the same AS. One of the main points to remember about iBGP relationships is that iBGP assumes that all of the routers within a single AS are fully meshed.
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