Distance-Vector Protocols
39
entire routing table as with classful routing protocols. If no changes occur,
classless routing protocols send Hello messages to their directly connected
neighbors. This ensures that the neighbors are still alive. Only if a router
does not receive a Hello message from its neighbor will a convergence of the
network take place.
Distance-Vector Protocols
T
here are four different distance-vector routing algorithms supported
by Cisco routers. Table 2.2 shows the different protocols available along
with their characteristics. RIP and IGRP use the Bellman-Ford algorithm.
EIGRP uses the Diffusing Update-based Algorithm (DUAL).
EIGRP is considered an advanced distance-vector routing algorithm, and
Cisco lists it as a distance-vector routing algorithm in their BSCN course. How-
ever, since it uses both the characteristics of distance-vector and link-state, it
is really considered a hybrid routing protocol. EIGRP will be discussed in
detail in Chapter 6, "IGRP and EIGRP."
T A B L E 2 . 2
Distance-Vector Comparisons
Characteristic
RIPv1
RIPv2
IGRP
EIGRP
Count to infinity
X
X
X
Split horizon with
poison reverse
X
X
X
X
Hold-down timer
X
X
X
Triggered updates
with route
poisoning
X
X
X
X
Load balancing
with equal paths
X
X
X
X
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w w w . s y b e x . c o m