Even though it is compatible with IGRP, EIGRP
operates quite differently than its predecessor. As an advanced
distance-vector routing protocol, EIGRP acts like a link-state protocol
when updating neighbors and maintaining routing information. EIGRP's
advantages over simple distance-vector protocols include the following:
- Rapid convergence - EIGRP routers
converge quickly because they rely on a state-of-the-art routing
algorithm called the Diffusing Update Algorithm (DUAL). DUAL
guarantees loop-free operation at every instant throughout a route
computation and allows all routers involved in a topology change to
synchronize at the same time.
- Efficient use of bandwidth -
EIGRP makes efficient use of bandwidth by sending partial, bounded
updates and its minimal consumption of bandwidth when the network is
stable.
- Partial, bounded updates - EIGRP routers
make partial, incremental updates rather than sending their complete
tables. This may remind you of OSPF operation, but unlike OSPF
routers, EIGRP routers send these partial updates only to the routers
that need the information, not to all routers in an area. For this
reason, they are called bounded updates.
- Minimal consumption of bandwidth when
the network is stable - Instead of using timed routing updates; EIGRP
routers keep in touch with each other using small hello packets.
Though exchanged regularly, hello packets do not eat up a significant
amount of bandwidth.
- Support for VLSM and CIDR - Unlike IGRP,
EIGRP offers full support for classless IP by exchanging subnet masks
in routing updates.
- Multiple network-layer support - EIGRP
supports IP, IPX, and AppleTalk through protocol-dependent modules (PDMs).
- Independence from routed
protocols - PDMs protect EIGRP from painstaking revision. Evolution of
a routed protocol, such as IP, may require a new protocol module, but
not necessarily a reworking of EIGRP itself.
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