|
A count to infinity problem can be avoided
by using holddown timers:
- When a router receives an update
from a neighbor indicating that a previously accessible network is
now inaccessible, the router marks the route as inaccessible and
starts a holddown timer. If at any time before the holddown timer
expires an update is received from the same neighbor indicating that
the network is again accessible, the router marks the network as
accessible and removes the holddown timer.
- If an update arrives from a
different neighboring router with a better metric than originally
recorded for the network, the router marks the network as accessible
and removes the holddown timer.
- If at any time before the holddown
timer expires an update is received from a different neighboring
router with a poorer metric, the update is ignored. Ignoring an
update with a poorer metric when a holddown timer is in effect
allows more time for the knowledge of a disruptive change to
propagate through the entire network.
|
Web Links