Configuring BGP4
December 2005
© Foundry Networks, Inc.
21 - 47
Defining IP Prefix Lists
An IP prefix list specifies a list of networks. When you apply an IP prefix list to a neighbor, the Layer 3 Switch
sends or receives only a route whose destination is in the IP prefix list. You can configure up to 100 prefix lists.
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:
FESX424 Router(config)# ip prefix-list Routesfor20 permit 20.20.0.0/24
FESX424 Router(config)# router bgp
FESX424 Router(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 20.20.0.0/24.
The
neighbor
command configures the Layer 3 Switch to use IP prefix list Routesfor20 to determine which routes
to send to neighbor 10.10.10.1. The Layer 3 Switch 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. You can configure
up to 100 prefix list entries. 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, see “Adding BGP4 Neighbors” on
page 21-12.
Defining Neighbor Distribute Lists
A neighbor distribute list is a list of BGP4 address filters or ACLs that filter the traffic to or from a neighbor. To
configure a neighbor distribute list, use either of the following methods.
To configure a distribute list that uses ACL 1, enter a command such as the following:
FESX424 Router(config-bgp-router)# neighbor 10.10.10.1 distribute-list 1 in
This command configures the Layer 3 Switch to use ACL 1 to select the routes that the Layer 3 Switch will accept
from neighbor 10.10.10.1.
Syntax:
neighbor <ip-addr> distribute-list <name-or-num> in | out
The <ip-addr> parameter specifies the neighbor.
Содержание FastIron Edge Switch X424
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