Solution to Contest #3: How good is your BGP?

Thanks to everyone that participated in Contest #3. Here are the solutions to both questions:

Question 1: eBGP peering with Loopback interfaces

There are actually three possible solutions to this:

1. Use the neighbor x.x.x.x ebgp-multihop 2 command
2. Use the neighbor x.x.x.x disable-connected-check command
3. Use the neighbor x.x.x.x ttl-security hops 2 command

Many people think that it takes two hops to get from the loopback interface of one router to the loopback interface of a directly connected router but this is not true: it actually takes just one hop. You can refer to this article that attempts to clear up this misunderstanding.

Contest #3: How good is your BGP?

Let’s up the stakes for this contest by giving two questions instead of one unlike what we have done for previous contests. This contest will focus on the workings of the Border Gateway Protocol (BGP). The first question deals with how to tweak the default behavior of BGP to suit our needs. The second question presents a troubleshooting scenario which involves BGP.