Rip; Introduction - Raisecom ISCOM2600G-HI (A) Series Configuration Manual

Raisecom
ISCOM2600G-HI (A) Series Configuration Guide

5.6 RIP

5.6.1 Introduction

Routing Information Protocol (RIP) is a simple Interior Gateway Protocol (IGP) based on
distance-vector algorithm.
Definition of distance
RIP defines the distance as below:


The distance is also called hops. RIP allows a path to cover up to 15 routers, so the distance of
16 indicates an unreachable network.
If two routes with unequal rate or bandwidth to the same destination are present but hops are
the same, RIP regards them as the same distance.
Working principles
Step 1 RIP starts initialization. When RIP starts initialization, it sends a request packet on every
participant interface. The request packet is used to request a complete routing table from all
RIP routers. It is broadcasted in a LAN or sent to the next hop in a point-to-point link. As a
special request, it requests complete route update from neighboring devices.
Step 2 Receive the request. RIP has two types of messages: the response message and receiving
message. Each route entry in the request packet will be processed to establish matrix and path
for routes. RIP uses hops as matrix; in other words, the value 1 indicates a directly connected
network while the value 16 indicates an unreachable network. The router sends back the entire
routing table as the response message.
Step 3 Receive the message and respond. The router receives and processes the response message by
adding, deleting, or modifying routing entries in the routing table.
Step 4 Update common routes and configure timers. By default, the router sends the entire routing
table as a response message to neighboring routers. When it receives a new route or updated
route, it will start a timer of 180s. If it receives no update message within 180s, it will
configure hops to 16. It then advertises the route with the matrix of 16 and deletes the route
after the Flush timer expires. The Flush timer is usually 240s, 60s longer than the expiration
timer. The device also supports the suppression timer which is 180s and starts after it receive
a route with a higher matrix. During the suppression time, the router will not update the
routing table according to its new received route. In this case, it provides an extra time for
network convergence.
Step 5 Trigger route update. When the matrix of a route changes, the routers sends related routes
rather than the entire routing table.
Features
The router running RIP exchanges information with neighboring routers only. If two routers
communicate without passing another router, they are neighbors to each other. As defined by
RIP, non-neighboring routers do not exchange information.
The distance from a route to its directly connected network is 1.
The distance from a route to its indirectly connected network increases by 1 every time
when the distance covers a router.
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