Routing Information Protocol
Sarhad University PeshawarSarhad University Peshawar
Computer Networks & Internetworking
RIP -- What is it?
RIP is a routing protocol for exchanging routing table information
• Routing updates must be passed between routers so that they can make the
proper choice on how to route a packet.
Distance vector routing protocol.
Uses hop count as a path selection metric.
Three types of timers.
Multiple stability features.
Distance Vector Routing Protocol
Each router sends all
or part of its routing
table in routing updates.
However, the updates
are only sent to
Cisco Systems Inc.
Hop Count -- Fifteen Hop Limit
Hop count is the sum of all the legs in a route.Hop count is the sum of all the legs in a route.
– After 15 hops, the packet is discardedAfter 15 hops, the packet is discarded
By default, routers send updates every 30 seconds.
A small random number is added to prevent collisions.
A route timeout timer is associated with a route. When it
expires, the route is marked invalid.
After the route timeout expires, the route-flush timer
eventually expires, deleting the route from the table.
Multiple Stability Features
Information learned about a route is not sent
back out the interface it was learned from.
When a link in a route fails, that route is put in
a hold-down state, where routers neither send
or receive updates about that route.
A -- Command - request or response.
B -- Version # - specifies version of RIP.
C -- Zero - Not used.
D -- Address Family Identifier (AFI) - Indicates
type of address being specified (IP, IPX, etc)
E -- Address - Specifies IP address of entry.
F -- Metric - # of hops traversed from source to
1 1 2 2 2 4 4 4 4
A B C D C E C C F
RIP version 1 does not recognize subnets.
This feature was added in RIP version 2.
Because RIP only uses hop count as a metric,
packets may be forced to take a slower route with
less hops over a faster route with more hops.
Other routing protocols use a combination of
different metrics to calculate a route.