Advanced EIGRP Configuration (Cont.)

Customizing the EIGRP Hello Interval and Hold Time

The ASA periodically sends hello packets to discover neighbors and to learn when neighbors become unreachable or inoperative. By default, hello packets are sent every 5 seconds.

The hello packet advertises the ASA hold time. The hold time indicates to EIGRP neighbors the length of time the neighbor should consider the ASA reachable. If the neighbor does not receive a hello packet within the advertised hold time, then the ASA is considered unreachable. By default, the advertised hold time is 15 seconds (three times the hello interval).

Both the hello interval and the advertised hold time are configured on a per-interface basis. We recommend setting the hold time to be at minimum three times the hello interval.

To configure the hello interval and advertised hold time, perform the following steps:

Detailed Steps

	Command	Purpose
Step 1	interface phy_if Example: hostname(config)# interface phy_if	Enter interface configuration mode for the interface on which you are configuring hello interval or advertised hold time.
Step 2	hello-interval eigrp as-num seconds Example: hostname(config)# hello-interval eigrp 2 60	This step allows you to change the hello interval.
Step 3	hold-time eigrp as-num seconds Example: hostname(config)# hold-time eigrp 2 60	This step allows you to change the hold time.

Disabling Automatic Route Summarization

Automatic route summarization is enabled by default. The EIGRP routing process summarizes on network number boundaries. This can cause routing problems if you have non-contiguous networks.

For example, if you have a router with the networks 192.168.1.0, 192.168.2.0, and 192.168.3.0 connected to it, and those networks all participate in EIGRP, the EIGRP routing process creates the summary address 192.168.0.0 for those routes. If an additional router is added to the network with the networks 192.168.10.0 and 192.168.11.0, and those networks participate in EIGRP, they will also be summarized as 192.168.0.0. To prevent the possibility of traffic being routed to the wrong location, you should disable automatic route summarization on the routers creating the conflicting summary addresses.

To disable automatic router summarization, enter the following command in router configuration mode for the EIGRP routing process:

Detailed Steps

	Command	Purpose
Step 1	router eigrp as-num Example: hostname(config)# router eigrp 2	This creates an EIGRP routing process, and the user enters router configuration mode for this EIGRP process. The as-num argument is the autonomous system number of the EIGRP routing process.
Step 2	no auto-summary Example: hostname(config-router)# no auto-summary	Automatic summary addresses have an adminstrative distance of 5. You cannot configure this value.

Disabling EIGRP Split Horizon

Split horizon controls the sending of EIGRP update and query packets. When split horizon is enabled on an interface, update and query packets are not sent for destinations for which this interface is the next hop. Controlling update and query packets in this manner reduces the possibility of routing loops.

By default, split horizon is enabled on all interfaces.

Split horizon blocks route information from being advertised by a router out of any interface from which that information originated. This behavior usually optimizes communications among multiple routing devices, particularly when links are broken. However, with nonbroadcast networks, there may be situations where this behavior is not desired. For these situations, including networks in which you have EIGRP configured, you may want to disable split horizon.

If you disable split horizon on an interface, you must disable it for all routers and access servers on that interface.

To disable EIGRP split-horizon, perform the following steps:

Detailed Steps

	Command	Purpose
Step 1	interface phy_if Example: hostname(config)# interface phy_if	Enter interface configuration mode for the interface on which you are changing the delay value used by EIGRP.
Step 2	no split-horizon eigrp as-number Example: hostname(config-if)# no split-horizon eigrp 2	This step disables the split horizon.

Monitoring EIGRP

You can use the following commands to monitor the EIGRP routing process. For examples and descriptions of the command output, see the Cisco Security Appliance Command Reference. Additionally, you can disable the logging of neighbor change message and neighbor warning messages

To monitor or disable various EIGRP routing statistics, perform one of the following tasks:

Command	Purpose
Monitoring EIGRP Routing
show eigrp [as-number] events [{start end} | type]	Displays the EIGRP event log.
show eigrp [as-number] neighbors [detail | static] [if-name]	Displays the EIGRP neighbor table.
show eigrp [as-number] interfaces [if-name] [detail]	Displays the interfaces participating in EIGRP routing.
show eigrp [as-number] topology [ip-addr [mask] | active | all-links | pending | summary | zero-successors]	Displays the EIGRP topology table.
show eigrp [as-number] traffic	Displays EIGRP traffic statistics.
router-id	Displays the router-id for this EIGRP process.
Disabling EIGRP Logging Messages
no eigrp log-neighbor-changes	Disables the logging of neighbor change messages. Enter this command in router configuration mode for the EIGRP routing process.
no eigrp log-neighbor-warnings	Disables the logging of neighbor warning messages.