PLANET ADN-4000 - Manual (Page 82)

3.3.7.3 RIP
Background
The Routing Information Protocol, or RIP, as it is more commonly called, is one of the most
enduring of all routing protocols. RIP is also one of the more easily confused protocol
because a variety of RIP-like routing protocols proliferated, some of which even used
the same name! RIP and the myriad RIP-like protocols were based on the same set of
algorithms that u
s
se distance vectors to mathematically compare routes to identify the best
not available in RIP.
rizes the basic capabilities and features associated with RIP. Topics
eflect the new route. The metric value for the path is increased
by 1, and the sender is indicated as the next hop. RIP routers maintain only the best route
(the route with the lowest metric value) to a destination. After updating its routing table, the
router immediately begins transmitting routing updates to inform other network routers of
the change. These updates are sent independently of the regularly scheduled updates that
RIP routers send
path to any given destination address. These algorithms emerged from academic research
that dates back to 1957. Today's open standard version of RIP, sometimes referred to as IP
RIP, is formally defined in two documents: Request For Comments (RFC) 1058 and
Internet Standard (STD) 56. As IP-based networks became both more numerous and
greater in size, it became apparent to the Internet Engineering Task Force (IETF) that RIP
needed to be updated. Consequently, the IETF released RFC 1388 in January 1993, which
was then superseded in November 1994 by RFC 1723, which describes RIP 2 (the second
version of RIP). These RFCs described an extension of RIP's capabilities but did not
attempt to obsolete the previous version of RIP. RIP 2 enabled RIP messages to carry
more information, which permitted the use of a simple authentication mechanism to secure
table updates. More importantly, RIP 2 supported subnet masks, a critical feature that was
This chapter summa
include the routing update process, RIP routing metrics, routing stability, and routing timers.
Routing Updates
RIP sends routing-update messages at regular intervals and when the network topology
changes. When a router receives a routing update that includes changes to an entry, it
updates its routing table to r
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