Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 67)

Brocade ICX 6650 Layer 3 Routing Configuration Guide 49
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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 192.168.22.x, enter the
following commands.
Brocade(config)# ip route 192.168.22.0 255.255.255.0 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 192.168.22.0/24 instead of 192.168.22.0 255.255.255.0.
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.
Configuring load balancing and redundancy
using multiple static routes to the same destination
You can configure multiple static IP routes to the same destination, for the following benefits:
• IP load sharing – If you configure more than one static route to the same destination, and the
routes have different next-hop gateways but have the same metrics, the Layer 3 Switch load
balances among the routes using basic round-robin. For example, if you configure two static
routes with the same metrics but to different gateways, the Layer 3 Switch alternates between
the two routes. For information about IP load balancing, refer to
“Configuring IP load sharing”
on page 55.