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Chapter 38
Configuring IP Unicast Routing
Configuring EIGRP
If the switch is running the IP base image, you can configure complete EIGRP routing. However, the
Note
configuration is not implemented because the IP base image supports only EIGRP stub routing.
After you have entered the eigrp stub router configuration command, only the eigrp stub connected
summary command takes effect. Although the CLI help might show the receive-only and static
keywords, and you can enter these keywords, the switch running the IP base image always behaves as if
the connected and summary keywords were configured.
Enhanced IGRP (EIGRP) is a Cisco-proprietary enhanced version of the IGRP. EIGRP uses the same
distance vector algorithm and distance information as IGRP; however, the convergence properties and
the operating efficiency of EIGRP are significantly improved.
The convergence technology employs an algorithm referred to as the diffusing update algorithm
(DUAL), which guarantees loop-free operation at every instant throughout a route computation. All
devices involved in a topology change can synchronize at the same time. Routers that are not affected by
topology changes are not involved in recomputations.
IP EIGRP provides increased network width. With RIP, the largest possible width of your network is
15 hops. Because the EIGRP metric is large enough to support thousands of hops, the only barrier to
network expansion is the transport-layer hop counter. EIGRP increments the transport control field only
when an IP packet has traversed 15 routers and the next hop to the destination was learned through
EIGRP. When a RIP route is used as the next hop to the destination, the transport control field increments
as usual.
EIGRP offers these features:
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EIGRP has these four basic components:
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Fast convergence.
Incremental updates when the state of a destination changes rather than sending the entire contents
of the routing table, minimizing the bandwidth required for EIGRP packets.
Less CPU usage because full update packets need not be processed each time they are received.
Protocol-independent neighbor discovery mechanism to learn about neighboring routers.
Variable-length subnet masks (VLSMs).
Arbitrary route summarization.
Scalable for large networks.
Neighbor discovery and recovery is the process that routers use to dynamically learn of other routers
on their directly attached networks. Routers must also discover when their neighbors become
unreachable or inoperative. Neighbor discovery and recovery is achieved by periodically sending
small hello packets. As long as hello packets are received, the Cisco IOS software learns that a
neighbor is alive and functioning. When this status is determined, the neighboring routers can
exchange routing information.
The reliable transport protocol is responsible for guaranteed, ordered delivery of EIGRP packets to
all neighbors. It supports intermixed transmission of multicast and unicast packets. Some EIGRP
packets must be sent reliably, and others need not be. For efficiency, reliability is provided only
when necessary. For example, on a multi-access network with multicast capabilities (such as
Ethernet), it is not necessary to send hellos reliably to all neighbors individually. Therefore, EIGRP
sends a single multicast hello with an indication in the packet informing the receivers that the packet
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
Configuring EIGRP
38-37
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