Dell BigIron RX Series, Configuration Manual

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202 BigIron RX Series Configuration Guide
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Configuring forwarding parameters
7
The distance <num> parameter specifies the administrative distance of the route. When
comparing otherwise equal routes to a destination, the device prefers lower administrative
distances over higher ones, so make sure you use a low value for your default route. Possible
values: 1 - 255. Default: 1.
NOTE
The device will replace the static route if it receives a route with a lower administrative distance.
Refer to
“Changing administrative distances” on page 767 for a list of the default administrative
distances for all types of routes.
Configuring a “null” route
You can configure the device to drop IP packets to a specific network or host address by configuring
a “null” (sometimes called “null0”) static route for the address. When the device receives a packet
destined for the address, the device drops the packet instead of forwarding it.
To configure a null static route to drop packets destined for network 209.157.22.x, enter the
following commands.
BigIron RX(config)# ip route 209.157.22.0 255.255.255.0 null0
BigIron RX(config)# write memory
Syntax: ip route <ip-addr> <ip-mask> | <dest-ip-addr>/<mask-bits> null0 [<metric>] [tag <num>]
[distance <num>]
To display the maximum value for your device, enter the show default values command. The
maximum number of static IP routes the system can hold is listed in the ip-static-route row in the
System Parameters section of the display. To change the maximum value, use the system-max
ip-static-route <num> command at the global CONFIG level.
The <ip-addr> parameter specifies the network or host address. The device will drop packets that
contain this address in the destination field instead of forwarding them.
The <ip-mask> parameter specifies the network mask. Ones are significant bits and zeros allow
any value. For example, the mask 255.255.255.0 matches on all hosts within the Class C subnet
address specified by
<ip-addr> . Alternatively, you can specify the number of bits in the network
mask. For example, you can enter 209.157.22.0/24 instead of 209.157.22.0 255.255.255.0.
The null0 parameter indicates that this is a null route. You must specify this parameter to make
this a null route.
The <metric> parameter adds a cost to the route. You can specify from 1 – 16. The default is 1.
The tag <num> parameter specifies the tag value of the route. Possible values: 0 - 4294967295.
Default: 0.
The distance <num> parameter configures the administrative distance for the route. You can
specify a value from 1 – 255. The default is 1. The value 255 makes the route unusable.
NOTE
The last three parameters are optional and do not affect the null route, unless you configure the
administrative distance to be 255. In this case, the route is not used and the traffic might be
forwarded instead of dropped.