Information Technology Reference
In-Depth Information
Prefix length included in route entry.
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Administrative distance for RIPv2 is 120.
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Not scalable. Used in small networks.
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Cisco Systems released EIGRP in the early 1990s as an evolution of IGRP toward a more
scalable routing protocol for large internetworks. EIGRP is a classless protocol that per-
mits the use of VLSMs and that supports CIDR for the scalable allocation of IP addresses.
EIGRP does not send routing updates periodically, as does IGRP. EIGRP allows for au-
thentication with MD5. EIGRP autosummarizes networks at network borders and can
load share over unequal-cost paths. Packets using EIGRP use IP 88. Only Cisco routers
can use EIGRP.
EIGRP is an advanced distance-vector protocol that implements some characteristics simi-
lar to those of link-state protocols. Some Cisco documentation refers to EIGRP as a hy-
brid protocol. EIGRP advertises its routing table to its neighbors as distance-vector
protocols do, but it uses hellos and forms neighbor relationships as link-state protocols do.
EIGRP sends partial updates when a metric or the topology changes on the network. It
does not send full routing-table updates in periodic fashion as do distance-vector proto-
cols. EIGRP uses Diffusing Update Algorithm (DUAL) to determine loop-free paths to
destinations. This section discusses DUAL.
By default, EIGRP load balances traffic if several paths have equal cost to the destination.
EIGRP performs unequal-cost load sharing if you configure it with the
variance
n
com-
mand. 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 net-
work boundaries.
EIGRP internal routes have an administrative distance of 90. EIGRP summary routes have
an administrative distance of 5, and EIGRP external routes (from redistribution) have an
administrative distance of 170.
EIGRP Components
EIGRP has four components that characterize it:
Protocol-dependent modules
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Key
To p i c
Neighbor discovery and recovery
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Reliable Transport Protocol (RTP)
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Diffusing Update Algorithm (DUAL)
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Yo u s h o u l d k n o w t h e r o l e o f t h e E I G R P c o m p o n e n t s , w h i c h a r e d e s c r i b e d i n t h e fo l l o w i n g
sections.
