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Routing Information Protocol (RIP)

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network, but it has a maximum allowable hop count of 15 by default, mean-
ing that 16 is deemed unreachable. RIP works well in small networks, but it
is inefficient on large networks with slow WAN links or on networks with a
large number of routers installed.

RIP version 1 uses only classful routing, which means that all devices

in the network must use the same subnet mask. This is because RIP version 1
does not send updates with subnet mask information in tow. RIP version
2 provides what is called prefix routing and does send subnet mask infor-
mation with the route updates. This is called classless routing. Only RIP
version 1 is discussed in this book because that is what the CCNA objec-
tives cover.

RIP Timers

RIP uses three different kinds of timers to regulate its performance:

Route update timer Sets the interval (typically 30 seconds) between
periodic routing updates, in which the router sends a complete copy of its
routing table out to all neighbors.

Route invalid timer

Determines the length of time that must elapse

(90 seconds) before a router determines that a route has become
invalid. It will come to this conclusion if it hasn't heard any updates
about a particular route for that period. When that happens, the router
will send out updates to all its neighbors letting them know that the
route is invalid.

Route flush timer

Sets the time between a route becoming invalid and

its removal from the routing table (240 seconds). Before it is removed
from the table, the router notifies its neighbors of that route's impend-
ing doom. The value of the route invalid timer must be less than that of
the route flush timer. This is to provide the router with enough time
to tell its neighbors about the invalid route before the routing table is
updated.

Configuring RIP Routing

To configure RIP routing, just turn on the protocol with the router rip
command and tell the RIP routing protocol which networks to advertise.

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