Standard
The static route consists of a destination network address or host, a corresponding network mask, and the IP
address of the next-hop IP address.
Null (discard)
The null route consists of the destination network address or host, a corresponding network mask, and either
the
reject
or
blackhole
keyword. Typically, the null route is configured as a backup route for discarding
traffic if the primary route is unavailable. By default, when IP routing is enabled, a route for the 127.0.0.0/8
network is created to the null interface. Traffic to this interface is rejected (dropped.)
This route is for all traffic to the "loopback" network, with the single exception of traffic to the host address of the
switch's loopback interface (127.0.0.1/32.) Figure A-3 on page 1-6 shows the default null route entry in the
switch's routing table.
NOTE:
On a single routing switch you can create one null route to a given destination. Multiple null routes to
the same destination are not supported.
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.
Chapter 6 Static Routing
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