Chapter 6: EBGP Configuration and Testing

JNCIP Lab Skills Covered in this Chapter:

• EBGP peering

  • Multihop and multipan

  • EBGP authentication

• Routing policy

  • Route damping

  • Martian filters

  • Local preference, MED, next hop self, etc.

• Miscellaneous EBGP knpbs

This chapter details JNCIP-level EBGP and service provider (SP) routing policy configuration scenarios, and provides examples of the verification methods that can be used to confirm proper EBGP and policy operation. It is assumed that the configurations of the routers in your test bed currently reflect the case study criteria presented at the end of Chapter 5, “IBGP Configuration and Testing,” which was built on top of the router configurations created during the OSPF case study in Chapter 3, “OSPF Configuration and Testing.” You will now be adding EBGP functionality to your test bed, and a functional IGP and IBGP configuration is required for proper EBGP and routing policy operation. If you are unsure as to the state of your routers, you should compare your configurations against those provided in the case studies at the end of Chapters 1, 2, 3, and 5. Verify that all of your router interfaces, your OSPF IGP, and your IBGP case study configuration are operational before proceeding.

EBGP may need the services of your IGP to resolve next hops, but like IBGP, it does not really care about the particulars of your IGP so the EBGP configuration tasks presented in this chapter could easily be applied to a test bed running IS-IS, or even RIP! Using the OSPF case study configuration is highly recommended, however, because this will simplify the task of following the OSPF-based examples presented in this chapter.

Proper EBGP operation is a significant factor in the overall success of your network. Making serious mistakes with EBGP will impact your ability to demonstrate proper routing policy, and may even cause your network to operate erratically due to the large number of routes present in a complete BGP routing table. The reader should bear in mind that it can be difficult to fully separate the operation of IBGP and EBGP. Due to their interdependence, the configuration specifics of one may cause problems in the other. A good example would be the typical need for a next hop self policy on IBGP peering sessions to prevent unusable next hops from producing hidden BGP routes. A JNCIP exam candidate must be proficient in the configuration, testing, and troubleshooting of all things BGP if the candidate’s resulting SP policy is to have any chance of working correctly.

Although the application of routing policy has been demonstrated throughout this book, most of your policy-related activities in the JNCIP examination are likely to be associated with the need to handle and process EBGP routes in typical SP fashion. In the end, you will likely agree that this chapter involves more routing policy–related activities than actual EBGP configuration, despite the chapter’s “EBGP” title.

This chapter concludes with a case study designed to closely approximate a typical JNCIP routing policy and EBGP configuration scenario. The results of key operational mode commands are provided in the case study analysis section so that you can also compare the behavior of your network to a known good example. Sample router configurations that meet all case study requirements are provided at the end of the case study for comparison with your own configurations.