Answers to Chapter 1 Review Questions

1:	What is the current version of EGP?
A:	The current version of EGP is 2.
2:	What is an EGP interior neighbor? An EGP exterior neighbor?
A:	An EGP gateway's neighbor is interior if it is within the same AS. An exterior neighbor is in a different AS.
3:	What is the primary difference between an EGP stub gateway and an EGP core gateway?
A:	Stub gateways can advertise only networks that are interior to their own AS. Core gateways can advertise both interior and exterior networks.
4:	Why does EGP use the concept of a core, or backbone, AS?
A:	EGP has no mechanisms for detecting loops . Therefore, a loop-free topology must be engineered physically so that inter-AS traffic must traverse a backbone.
5:	What is the difference between an active EGP neighbor and a passive EGP neighbor?
A:	An active neighbor initiates the peer relationship and sends Hellos to maintain it. Passive neighbors respond to Hellos with I-Heard-You messages.
6:	What is the purpose of an EGP Poll message?
A:	A Poll message is a request to a neighbor for an Update.
7:	What is an indirect, or third-party, neighbor?
A:	An indirect neighbor is a gateway that shares a common data link with another gateway and can reach certain networks through that gateway but is not peered directly with the gateway. Rather, it learns its reachability information from yet another gateway on the data link.
8:	How does EGP use its metrics to calculate the best path to a destination?
A:	Although EGP has a metric, it has no mechanism for determining best paths. Therefore, the metric is used only for indicating an unreachable network.