D-Link DES-3326SR User Manual page 110

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
advertised. If the route is not advertised for a period of time
(usually 180 seconds), the route is removed from the routing
table.
RIP does not have an explicit method to detect routing loops.
Many RIP implementations include an authorization
mechanism (a password) to prevent a router from learning
erroneous routes from unauthorized routers.
To maximize stability, the hop count RIP uses to measure
distance must have a low maximum value. Infinity (that is, the
network is unreachable) is defined as 16 hops. In other words,
if a network is more than 16 routers from the source, the local
router will consider the network unreachable.
RIP can also be slow to converge (to remove inconsistent,
unreachable or looped routes from the routing table) because
RIP messages propagate relatively slowly through a network.
Slow convergence can be solved by using split horizon update,
where a router does not propagate information about a route
back to the interface on which it was received. This reduces
the probability of forming transient routing loops.
Hold down can be used to force a router to ignore new route
updates for a period of time (usually 60 seconds) after a new
route update has been received. This allows all routers on the
network to receive the message.
A router can 'poison reverse' a route by adding an infinite (16)
hop count to a route's advertisement. This is usually used in
conjunction with triggered updates, which force a router to
send an immediate broadcast when an update of an
unreachable network is received.
98