If no appropriate route or backup
route exists in the local routing table, EIGRP queries its neighbors to discover an alternate
route.
172 Chapter 5: Implementing EIGRP
?– Reduced bandwidth usage: EIGRP does not make periodic updates. Instead, it sends partial
updates when the path or the metric changes for that route. When path information changes,
DUAL sends an update about only that link rather than about the entire table.
?– Multiple network layer support: EIGRP supports AppleTalk, IP version 4 (IPv4), IP version
6 (IPv6), and Novell Internetwork Packet Exchange (IPX), which use protocol-dependent
modules (PDM). PDMs are responsible for protocol requirements that are speci?¬?c to the
network layer.
?– Classless routing: Because EIGRP is a classless routing protocol, it advertises a routing
mask for each destination network. The routing mask feature enables EIGRP to support
discontiguous subnetworks and variable-length subnet masks (VLSM).
?– Less overhead: EIGRP uses multicast and unicast rather than broadcast. As a result, end
stations are unaffected by routing updates and requests for topology information.
?– Load balancing: EIGRP supports unequal metric load balancing, which allows
administrators to better distribute traf?¬?c ?¬‚ow in their networks.
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