Cisco ASA 5505 - Manual (Page 509)

C H A P T E R
27-1
Cisco ASA 5500 Series Configuration Guide using the CLI
27
Configuring EIGRP
This chapter describes how to configure the ASA to route data, perform authentication, and redistribute
routing information using the Enhanced Interior Gateway Routing Protocol (EIGRP).
This chapter includes the following sections:
• Information About EIGRP, page 27-1
• Licensing Requirements for EIGRP, page 27-2
• Guidelines and Limitations, page 27-2
• Configuring EIGRP, page 27-3
• Customizing EIGRP, page 27-4
• Monitoring EIGRP, page 27-17
• Configuration Example for EIGRP, page 27-18
• Feature History for EIGRP, page 27-19
Information About EIGRP
EIGRP is an enhanced version of IGRP developed by Cisco. Unlike IGRP and RIP, EIGRP does not send
out periodic route updates. EIGRP updates are sent out only when the network topology changes. Key
capabilities that distinguish EIGRP from other routing protocols include fast convergence, support for
variable-length subnet mask, support for partial updates, and support for multiple network layer
protocols.
A router running EIGRP stores all the neighbor routing tables so that it can quickly adapt to alternate
routes. If no appropriate route exists, EIGRP queries its neighbors to discover an alternate route. These
queries propagate until an alternate route is found. Its support for variable-length subnet masks permits
routes to be automatically summarized on a network number boundary. In addition, EIGRP can be
configured to summarize on any bit boundary at any interface. EIGRP does not make periodic updates.
Instead, it sends partial updates only when the metric for a route changes. Propagation of partial updates
is automatically bounded so that only those routers that need the information are updated. As a result of
these two capabilities, EIGRP consumes significantly less bandwidth than IGRP.
Neighbor discovery is the process that the ASA uses to dynamically learn of other routers on directly
attached networks. EIGRP routers send out multicast hello packets to announce their presence on the
network. When the ASA receives a hello packet from a new neighbor, it sends its topology table to the
neighbor with an initialization bit set. When the neighbor receives the topology update with the
initialization bit set, the neighbor sends its topology table back to the ASA.