Allied Telesis AT-S63 - Manual (Page 554)

Chapter 32: Internet Protocol Version 4 Packet Routing
554 Section VII: Internet Protocol Routing
Dynamic RIP routes are removed from the table when they are not kept up
to date (refreshed) by the neighboring routers. The metric of a route that is
not refreshed is increased to 16 to indicate an unreachable network. If the
route is not updated after 180 seconds, it is deleted from the table.
The switch does not permit duplicate routes with identical destination IP
addresses in the routing table. It does, however, allow the addition of a
route with a more general IP address of a preexisting address, but not a
more specific address. For instance, a new route to 149.44.0.0 (mask
255.255.0.0) is permitted even when the table already contains a static or
dynamic route to the subnet 149.44.22.0 (mask 255.255.255.0), because
the new route is more general than the preexisting route. The more
specific route would be used to route packets to the 149.44.22.0 subnet
and the more general route for all other packets with a destination address
in the 149.44.0.0 network.
The switch, however, does not accept a more specific route of a
preexisting route. As an example, a new static or dynamic route to
149.55.44.0 is rejected if the route to 149.55.0.0 is already in the table.
Here are other items concerning the routing table:
ˆ The switch does not permit the substitution of one static route for
another. To change the attributes of an existing static route, such as
the next hop or metric value, you could modify it using the “SET IP
ROUTE” on page 588 or delete it and add the route again with the new
information, using “ADD IP ROUTE” on page 574.
ˆ The switch does not permit the substitution of a static route for a
dynamic RIP route. The converse is equally true, as well. For instance,
a static route to a remote destination cannot be added if the switch has
already learned the route dynamically with RIP. Conversely, to replace
a static route with a dynamic route, the static route must be deleted
and the switch allowed to learn the route dynamically with RIP.
ˆ If the switch is running RIP, a new dynamic route with a lower metric
value will replace a preexisting dynamic route. If the preexisting
dynamic route has the same or a lower metric value, the new route is
discarded and the timer on the preexisting route is refreshed.
ˆ An inactive interface route, where there are no active ports in the
VLAN, is not propagated by RIP.
The maximum storage capacity of the routing table in the AT-9400 Series
switch is:
ˆ 512 interface routes
ˆ 1024 static routes
ˆ 1024 RIP routes