Configuration Guide User guide
FastIron Configuration Guide 995
53-1002494-02
Configuring IP parameters – Layer 3 Switches
Configuring a “Null” route
You can configure the Layer 3 Switch 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 Layer 3
Switch receives a packet destined for the address, the Layer 3 Switch drops the packet instead of
forwarding it.
To configure a null static route, use the following CLI method.
To configure a null static route to drop packets destined for network 209.157.22.x, enter the
following commands.
Brocade(config)# ip route 209.157.22.0 255.255.255.0 null0
Brocade(config)# write memory
Syntax: ip route <ip-addr> <ip-mask> null0 [<metric>] [distance <num>]
or
Syntax: ip route <ip-addr>/<mask-bits> null0 [<metric>] [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 Layer 3 Switch 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 through 16. The default is
1.
The distance <num> parameter configures the administrative distance for the route. You can
specify a value from 1 through 255. The default is 1. The value 255 makes the route unusable.
NOTE
The last two 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.