Chapter 15

"Do I Know This Already?"

10.A, B, D
11.C and D


1.The command resets BGP peer associations, clears the BGP routing table, and re-establishes BGP connections to the neighbors. It should be used cautiously because the loss of connections will drop packets.
2.The command tells the router the IP address of the BGP neighbor and the autonomous system to which the neighbor belongs. This information allows the router to create a TCP session with the neighboring router and exchange BGP routing information.
3.The four message types of BGP are
  • Update messages: Contain paths to destination networks and their attributes. Routes that are no longer available or withdrawn routes are included in updates.

  • Open messages: Used to establish connections with peers.

  • Keepalives: Sent periodically between peers to maintain connections and verify paths held by the router sending the keepalive.

  • Notification: Used to inform the receiving router of errors.

4.A peer group is a group of BGP neighbors that share characteristics. The use of peer groups simplifies the configuration of BGP because one configuration effectively configures every router in the peer group. They are also more efficient because updates are generated once per peer group instead of on a per-router (peer) basis, reducing the resources required to support BGP.
5.In external BGP, there is no difference between a neighbor and a peer. A peer is the BGP term for a neighbor. Both terms refer to a router that is directly connected, with which routing information is exchanged. In iBGP, these routers are not necessarily physically adjacent, but they are the next logical hop router running BGP.
6.The network command permits BGP to advertise a network if it is present in the routing table. It is not responsible for starting the BGP process on an interface; instead, it identifies which networks the router originates.
7.On a broadcast multi-access network such as Ethernet, the next-hop address is the IP address of the advertising router. This command forces BGP to advertise itself as the next-hop router instead of letting the protocol determine the address to be used. This avoids problems seen on NBMA networks or nonmeshed environments, such as X.25 and Frame Relay.