Information Technology Reference
In-Depth Information
Classful protocol (no support for CIDR).
No support for VLSMs.
Composite metric of bandwidth and delay.
Load and reliability can be factored into the metric.
Route updates sent every 90 seconds.
104 routes per IGRP message.
No support for authentication.
Implements split horizon with poison reverse.
Implements triggered updates.
By default, equal-cost load balancing; unequal-cost load balancing with the variance
command.
Administrative distance is 100.
EIGRP
EIGRP was released in the early 1990s by Cisco Systems as a evolution of IGRP toward a
scalable routing protocol. EIGRP is a classless protocol that permits the use of VLSMs and sup-
port for CIDR for scalable allocation of IP addresses. Routing updates are not sent periodically,
as in IGRP. EIGRP allows for authentication, with simple passwords or with MD5. EIGRP
autosummarizes networks at network borders and can load balance over unequal-cost paths.
Packets use IP protocol 88. You can use only EIGRP on Cisco routers.
EIGRP is an advanced distance vector protocol that implements some characteristics similar to
link-state protocols. Some of Cisco's documentation might refer to EIGRP as a hybrid protocol.
EIGRP advertises its routing table to its neighbors as distance vector protocols do, but it uses
hellos and forms neighbor relationships similar to link-state protocols. EIGRP sends partial
updates when a metric or the topology changes on the network. Full routing table updates are
not sent in periodic fashion, as they are with distance vector protocols. EIGRP uses DUAL to
determine loop-free paths to destinations. DUAL is covered in this section.
By default, EIGRP loads balance traffic if there are several paths with equal-cost to the
destination. EIGRP does unequal-cost load balancing if configured with the variance n
command. EIGRP includes routes that are equal to or less than n times the minimum metric
route to a destination.
As in RIP and IGRP, EIGRP also summarizes IP networks at network boundaries. You can
disable autosummarization with the no auto-summary command as follows:
router eigrp 100
no auto-summary
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