Extreme Networks Summit1 - Manual (Page 151)

S UMMIT S WITCH I NSTALLATION AND U SER G UIDE 10-3
O VERVIEW OF RIP
O
VERVIEW OF
RIP
RIP is an Interior Gateway Protocol (IGP) first used in computer routing in the
ARPAnet as early as 1969. It is primarily intended for use in homogeneous networks of
moderate size.
To determine the best path to a distant network, a router using RIP always selects the
path that has the least number of hops. Each router that data must traverse is
considered to be one hop.
R OUTING T ABLE
The routing table in a router using RIP contains an entry for every known destination
network. Each routing table entry contains the following information:
• IP address of the destination network
• Metric (hop count) to the destination network
• IP address of the next router
• Timer that tracks the amount of time since the entry was last updated
The router exchanges an update message with each neighbor every 30 seconds (default
value), or if there is a change to the overall routed topology (also called triggered
updates). If a router does not receive an update message from its neighbor within the
route timeout period (180 seconds by default), the router assumes the connection
between it and its neighbor is no longer available.
S PLIT H ORIZON
Split horizon is a scheme for avoiding problems caused by including routes in updates
sent to the router from which the route was learned. Split horizon omits routes learned
from a neighbor in updates sent to that neighbor.
P OISON R EVERSE
Like split horizon, poison reverse is a scheme for eliminating the possibility of loops in
the routed topology. In this case, a router advertises a route over the same port that
supplied the route, but the route uses a hop count of 16, defining it as unreachable.
Summit.bk : 10PROT.FM Page 3 Thursday, June 18, 1998 9:27 AM