Convergence
47
Chapters 4 and 5 will discuss OSPF in detail, and Chapter 6 will discuss
EIGRP. We will discuss how both EIGRP and OSPF (as well as RIP and
IGRP) provide convergence in a network outage situation in the convergence
sections below.
Convergence
C
onvergence is the time it takes for all routers to agree on the network
topology after a change in the network. The routers basically synchronize
their routing tables.
There are at least two different detection methods used by all routing pro-
tocols. The first method is used by the Physical and Data Link layer proto-
cols. When the network interface on the router does not receive three
consecutive keepalives, the link will be considered down. The second method
is that when the routing protocol at the Network and Transport layers fails
to receive three consecutive Hello messages, the link will be considered
down.
After the link is considered down is where the routing protocols differ.
Routing protocols have timers that are used to stop network loops from
Load balancing with
unequal paths
X
Load balancing with
equal paths
X
X
X
VLSM support
X
X
X
Metric
Cost
Cost
Composite
Hop count limit
200
1024
100 by default
Support for size of
network
Large
Very Large
Large
T A B L E 2 . 3
Link-State Comparisons (continued)
Characteristic
OSPF
IS-IS
EIGRP
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