Cisco 7604 Configuration Guide - Page 165

Chapter 8 Configuring IP Routing and DHCP Services Configuring EIGRP The hello packets are sent out as multicast messages. No response is expected to a hello message. The exception to this is for statically defined neighbors. If you use the neighbor command to configure a neighbor, the hello messages sent to that neighbor are sent as unicast messages. Routing updates and acknowledgements are sent out as unicast messages. Once this neighbor relationship is established, routing updates are not exchanged unless there is a change in the network topology. The neighbor relationship is maintained through the hello packets. Each hello packet received from a neighbor contains a hold time. This is the time in which the FWSM can expect to receive a hello packet from that neighbor. If the FWSM does not receive a hello packet from that neighbor within the hold time advertised by that neighbor, the FWSM considers that neighbor to be unavailable. The EIGRP uses an algorithm called DUAL for route computations. DUAL saves all routes to a destination in the topology table, not just the least-cost route. The least-cost route is inserted into the routing table. The other routes remain in the topology table. If the main route fails, another route is chosen from the feasible successors. A successor is a neighboring router used for packet forwarding that has a least-cost path to a destination. The feasibility calculation guarantees that the path is not part of a routing loop. If a feasible successor is not found in the topology table, a route recomputation must occur. During route recomputation, DUAL queries the EIGRP neighbors for a route, who in turn query their neighbors. Routers that do no have a feasible successor for the route return an unreachable message. During route recomputation, DUAL marks the route as active. By default, the FWSM waits for three minutes to receive a response from its neighbors. If the FWSM does not receive a response from a neighbor, the route is marked as stuck-in-active. All routes in the topology table that point to the unresponsive neighbor as a feasibility successor are removed. Enabling and Configuring EIGRP Routing You can only enable one EIGRP routing process on the FWSM. To enable and configure EIGRP routing, perform the following tasks: Step 1 Step 2 Step 3 Create the EIGRP routing process and enter router configuration mode for that process by entering the following command: hostname(config)# router eigrp as-num The as-num argument is the autonomous system number of the EIGRP routing process. To configure the interfaces and networks that participate in EIGRP routing, configure one or more network statements by entering the following command: hostname(config-router)# network ip-addr [mask] Directly-connected networks that fall within the defined network are advertised by the FWSM. Additionally, only interfaces with an IP address that fall within the defined network participate in the EIGRP routing process. If you have an interface that you do not want to participate in EIGRP routing, but that is attached to a network that you want advertised, configure a network command that covers the network the interface is attached to, and use the passive-interface command to prevent that interface from sending or receiving EIGRP updates. (Optional) To prevent an interface from sending or receiving EIGRP routing message, enter the following command: OL-20748-01 Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM 8-23