Brocade Communications Systems FastIron SX 1600, Configuration Manual, Page: 407 / 593

Defining and applying IP prefix lists
An IP prefix list specifies a list of networks. When you apply an IP prefix list to a neighbor, the device sends or receives only a route
whose destination is in the IP prefix list. The software interprets the prefix lists in order, beginning with the lowest sequence number.
To configure an IP prefix list and apply it to a neighbor, enter commands such as the following.
device(config)# ip prefix-list Routesfor20 permit 10.20.0.0/24
device(config)# router bgp
device(config-bgp-router)# neighbor 10.10.10.1 prefix-list Routesfor20 out
These commands configure an IP prefix list named Routesfor20, which permits routes to network 10.20.0.0/24. The neighbor
command configures the device to use IP prefix list Routesfor20 to determine which routes to send to neighbor 10.10.10.1. The device
sends routes that go to 10.20.x.x to neighbor 10.10.10.1 because the IP prefix list explicitly permits these routes to be sent to the
neighbor.
Syntax: [no] ip prefix-list name [ seq seq-value ] [ description string ] deny | permit network-addr / mask-bits [ ge ge-value ] [ le le-
value ]
The name parameter specifies the prefix list name. Use this name when applying the prefix list to a neighbor.
The description string parameter is a text string describing the prefix list.
The seq seq-value parameter is optional and specifies the sequence number of the IP prefix list. If you do not specify a sequence
number, the software numbers the entries in increments of 5, beginning with prefix list entry 5. The software interprets the prefix list
entries in numerical order, beginning with the lowest sequence number.
The deny and permit parameters specify the action the software takes if a neighbor route is in this prefix list.
The network-addr and mask-bits parameters specify the network number and the number of bits in the network mask.
You can specify a range of prefix length for prefixes that are more specific than network-addr and mask-bits .
The prefix-list matches only on this network unless you use the ge ge-value or le le-value parameters.
• If you specify only ge ge-value , the mask-length range is from ge-value to 81.
• If you specify only le le-value , the mask-length range is from length to le-value .
The ge-value or le-value you specify must meet the following condition:
length < ge-value <= le-value <= 81
If you do not specify ge ge-value or le le-value , the prefix list matches only on the exact network prefix you specified with the network-
addr and mask-bits parameters.
In the following example, only default routes are allowed:
device(config)# ip prefix-list match-default-routes permit 0.0.0.0/0
In the following example, only default routes are denied:
device(config)# ip prefix-list match-default-routes deny 0.0.0.0/0
In the following example, all routes are allowed, including all subnet masks and all prefixes:
device(config)# ip prefix-list match-all-routes permit 0.0.0.0/0 le 32
NOTE
Be careful to determine exactly which routes you want to allow using a prefix
list.
Filtering
FastIron Ethernet Switch Layer 3 Routing
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