Multicast and Routing Guide K/KA/KB.15.15

Other sources of routes in the routing table
The IP route table can also receive routes from the following sources:
• Directly connected networks: One route is created per IP interface. When you add an IP
interface, the routing switch automatically creates a route for the network the interface is in.
• RIP: If RIP is enabled, the routing switch can learn about routes from the advertisements other
RIP routers send to the routing switch. If the RIP route has a lower administrative distance than
any other routes from different sources to the same destination, the routing switch places the
route in the IP route table.
• OSPF: See RIP, but substitute "OSPF" for "RIP".
• Default route: This is a specific static route that the routing switch uses if other routes to the
destination are not available.
Static IP route parameters
When you configure a static IP route, you must specify the following parameters:
• The IP address and network mask for the route's destination network or host.
• The route's path, which can be one of the following:
IP address of a next-hop router.•
• "Null" interface; the routing switch drops traffic forwarded to the null interface.
The routing switch also applies default values for the route's administrative distance (page A-10.)
In the case of static routes, this is the value the routing switch uses to compare a static route to
routes from other route sources to the same destination before placing a route in the IP route table.
The default administrative distance for static IP routes is 1, but can be configured to any value from
1 to 255.
The fixed administrative distance values ensure that the routing switch always prefers static IP routes
over routes from other sources to the same destination.
Static route states follow VLAN states
IP static routes remain in the IP route table only so long as the IP interface to the next-hop router is
up. If the next-hop interface goes down, the software removes the static route from the IP route
table. If the next-hop interface comes up again, the software adds the route back to the route table.
This feature allows the routing switch to adjust to changes in network topology. The routing switch
does not continue trying to use routes on unreachable paths, but instead uses routes only when
their paths are reachable.
For example, the following command configures a static route to 207.95.7.0 (with a network mask
of 255.255.255.0), using 207.95.6.157 as the next-hop router's IP address.
HP Switch(config)# ip route 207.95.7.0/24 207.95.6.157
A static IP route specifies the route's destination address and the next-hop router's IP address or
routing switch interface through which the routing switch can reach the destination. (The route is
added to the routing switch's IP route table.)
In the above example, routing switch "A" knows that 207.95.6.157 is reachable through port
A2, and assumes that local interfaces within that subnet are on the same port. Routing switch "A"
deduces that IP interface 207.95.7.188 is also on port A2. The software automatically removes
a static route from the route table if the next-hop VLAN used by that route becomes unavailable.
When the VLAN becomes available again, the software automatically re-adds the route to the
route table.
Static route types 127