Junos Enterprise Routing, 2nd Edition

Chapter Review Answers

1. Answer: D. The AS path attribute records each AS that a route update has passed through, and is updated on EBGP links. A BGP speaker discards received updates that contain the local ASN in the AS path.

2. Answer: B. The local preference attribute is evaluated early in the BGP decision process, before AS path, MED, origin, and so on.

3. Answer: B. The AS path attribute has global significance; once a value has been added, no other speaker can remove that ASN from the list because this would break BGP’s loop prevention. The AS path is considered early in the selection process, and so has a good chance of impacting forwarding decisions in remote ASs. MED does not transit the peer AS, local preference is not supported on EBGP links, and communities can be stripped.

4. Answer: B. The next hop is unchanged on IBGP updates, but it is rewritten on EBGP links. EBGP does not require a full mesh, because the AS path is updated on EBGP links.

5. Answer: B. Junos applies only the most specific policy applications, and a neighbor level is more specific than a group level, which is more specific than a global level. If you need a particular neighbor to execute what you consider a global, group, and neighbor policy, all three must be changed at the neighbor level.

6. Answer: A. The Idle state indicates an inability to route the session, and an established session is displayed with an x/x/x, for active, received, and damped routes, respectively.

7. Answer: B. The show route protocol bgp command shows ...