Chapter 3 Rip Configuration; Brief Introduction To Rip - Huawei Quidway S3500 Series Operation Manual

Operation Manual - Routing Protocol
Quidway S3500 Series Ethernet Switches

Chapter 3 RIP Configuration

3.1 Brief Introduction to RIP

Routing Information Protocol (RIP) is a relatively simple dynamic routing protocol, but it
has a wide application. RIP is a kind of Distance-Vector (D-V) algorithm-based protocol
and exchanges routing information via UDP packets. It employs Hop Count to measure
the distance to the destination host, which is called Routing Cost. In RIP, the hop count
from a router to its directly connected network is 0, and that to a network which can be
reached through another router is 1, and so on. To restrict the time to converge, RIP
prescribes that the cost value is an integer ranging 0 and 15. The hop count equal to or
exceeding 16 is defined as infinite, that is to say, the destination network or the host is
unreachable.
RIP sends routing refreshing message every 30 seconds. If no routing refreshing
message is received from one network neighbor in 180 seconds, RIP will tag all routes
of the network neighbor to be unreachable. If no routing refreshing message is received
from one network neighbor in 300 seconds, RIP will finally remove the routes of the
network neighbor from the routing table.
To improve the performances and avoid route loop, RIP supports Split Horizon, Poison
Reverse and allows importing the routes discovered by other routing protocols.
Each router running RIP manages a route database, which contains routing entries to
all the reachable destinations in the network. These routing entries contain the
following information:
Destination address: IP address of a host or network.
Next hop address: The address of the next router that an IP packet will pass
through for reaching the destination.
Output interface: The interface through which the IP packet should be forwarded.
Cost: The cost for the router to reach the destination.
Timer: Duration from the last time that the routing entry is modified till now. The
timer is reset to 0 whenever a routing entry is modified.
Route tag: Discriminate whether the route is generated by an interior routing
protocol or by an exterior routing protocol.
The whole process of RIP startup and running can be described as follows:
1) If RIP is enabled on a router for the first time, the router will broadcast or multicast
the request packet to the adjacent routers. Upon receiving the request packet, the
adjacent routers (on which, RIP should have been enabled) respond to the
request by returning the response packets containing information of their local
routing tables.
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Chapter 3 RIP Configuration