Defining and applying ip prefix lists – Brocade BigIron RX Series Configuration Guide User Manual
Page 953
BigIron RX Series Configuration Guide
875
53-1002484-04
Filtering
27
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.
BigIron RX(config)# ip prefix-list Routesfor20 permit 20.20.0.0/24
BigIron RX(config)# router bgp
BigIron RX(config-bgp)# neighbor 10.10.10.1 prefix-list Routesfor20 out
These commands configure an IP prefix list named Routesfor20, which permits routes to network
20.20.0.0/24. 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
20.20.x.x to neighbor 10.10.10.1 because the IP prefix list explicitly permits these routes to be sent
to the neighbor.
Syntax: 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. You 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 IP prefix list’s sequence number. If
you do not specify a sequence number, the software numbers them 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 | permit parameter specifies the action the software takes if a neighbor’s route is in this
prefix list.
The prefix-list matches only on this network unless you use the ge <ge-value> or le <le-value>
parameters. (See below.)
The <network-addr>/<mask-bits> parameter specifies 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>/<mask-bits>.
•
If you specify only ge <ge-value>, then the mask-length range is from <ge-value> to 32.
•
If you specify only le <le-value>, then 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 <= 32
If you do not specify ge <ge-value> or le <le-value>, the prefix list matches only on the exact
network prefix you specify with the <network-addr>/<mask-bits> parameter.
For the syntax of the neighbor command shown in the example above, refer to