JUNOS Enterprise Routing

Conclusion

BGP can have a dramatic impact on the operation of an enterprise network when the network is multihomed, and even more so when it is multihomed to multiple providers. BGP itself is not a very complex protocol, but the myriad ways in which its attributes are acted upon, and the cascading effects of advertising only what the local speaker considers the best route, often lead to an unanticipated result. To the uninitiated, this often leads to confusion and what might seem to be unpredictable behavior. JUNOS software provides a complete set of diagnostic tools, from the CLI’s operational mode displays to the extensive protocol tracing, which makes most BGP problems easy to diagnose. For example, the way the software displays why a given BGP path was not selected makes changing the results for that BGP decision step a straightforward matter, that is, whatever attribute caused the route to lose should be modified.

EBGP and IBGP are similar, but they have key differences in the way they are typically configured and in how they operate. This chapter detailed those differences and demonstrated typical EBGP physical peering and IBGP loopback-based peering. Because IBGP does not rewrite the next hop, you will often need a next hop self-policy or some other method of advertising the external EBGP peering address into your IGP.

Bringing up BGP peerings is really just the start of the process. BGP is all about policy and administrative control over route exchanges, and therefore forwarding ...