Enhanced Interior
Gateway Routing Protocol - EIGRP
Introduction
Enhanced Interior Gateway Routing
Protocol (EIGRP) is
another Cisco proprietary, hybrid (has feature of
Distance Vector and
Link State protocols),
interior gateway protocol (IGP) used by routers to
exchange routing information.
EIGRP uses a composite metric composed of
Bandwidth, Delay, Reliability, and Loading to determine
the best path between two locations.
EIGRP can route IP, IPX and
Appletalk. Along with IS-IS, it is one of the few
multi-protocol routing protocols.
The
Diffusing Update Algorithm (DUAL)
is the heart of EIGRP. In
essence, DUAL always keeps
a backup route in mind, in case the primary route goes
down. DUAL also limits how
many routers are affected when a change occurs to the
network.
There is no
maximum allowable number of hops. In a
EIGRP network, each router multi-casts "hello"
packs to discover its adjacent neighbor. This adjcency
database is shared with other router to build a topology
database. From the topology database the best route
(Successor) and the second best route (Feasible
Successor) is found.
EIGRP is classless, meaning
it does include the subnet mask in routing updates.
However, by default 'auto-summary' is enable. You must
disable if you want subnet information from other major
networks.
The
EIGRP metric is a can be a
complex calculation, but by default it only uses
bandwidth and delay to determine the best path. |
