User guide
12-4 E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
I
NTERIOR
G
ATEWAY
R
OUTING
P
ROTOCOLS
• 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 interface that
supplied the route, but the route uses a hop count of 16, defining it as unreachable.
T
RIGGERED
U
PDATES
Triggered updates occur whenever a router changes the metric for a route, and it is
required to send an update message immediately, even if it is not yet time for a regular
update message to be sent. This will generally result in faster convergence, but may also
result in more RIP-related traffic.
R
OUTE
A
DVERTISEMENT
OF
VLAN
S
VLANs that are configured with an IP address, but are configured to not route IP or are
not configured to run RIP, do not have their subnets advertised by RIP. Only those
VLANs that are configured with an IP address and are configured to route IP and run
RIP have their subnets advertised.