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Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
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Chapter 39 Configuring IP Unicast Routing
Configuring BGP
Before using a prefix list in a command, you must set up the prefix list. Beginning in privileged EXEC
mode, follow these steps to create a prefix list or to add an entry to a prefix list:
To delete a prefix list and all its entries, use the
no
ip prefix-list
list-name
global configuration
command. To delete an entry from a prefix list, use the
no
ip prefix-list seq
seq-value
global
configuration command. To disable automatic generation of sequence numbers, use the
no ip prefix-list
sequence number
command; to reenable automatic generation, use the
ip prefix-list sequence number
command. To clear the hit-count table of prefix list entries, use the
clear ip prefix-list
privileged EXEC
command.
Configuring BGP Community Filtering
One way that BGP controls the distribution of routing information is based on the value of the
COMMUNITIES attribute. The attribute groups destinations into communities and applies routing
decisions based on the communities. This method simplifies the configuration of a BGP speaker to
control distribution of routing information.
A
community
is a group of destinations that share some common attribute. Each destination can belong
to multiple communities. Autonomous-system administrators can define to which communities a
destination belongs. By default, all destinations belong to the general Internet community. The
community is identified by the COMMUNITIES attribute, an optional, transitive, global attribute in the
numerical range from 1 to 4294967200. These are some predefined, well-known communities:
•
internet
—Advertise this route to the Internet community. All routers belong to it.
•
no-export
—Do not advertise this route to EBGP peers.
•
no-advertise
—Do not advertise this route to any peer (internal or external).
•
local-as
—Do not advertise this route to peers outside the local autonomous system.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
ip prefix-list
list-name
[
seq
seq-value
]
deny
|
permit
network
/
len
[
ge
ge-value
] [
le
le-value
]
Create a prefix list with an optional sequence number to
deny
or
permit
access for matching conditions. You must enter at least one
permit
or
deny
clause.
•
network
/
len
is the network number and length (in bits) of the
network mask.
•
(Optional)
ge
and
le
values specify the range of the prefix length
to be matched.The specified
ge-value
and
le-value
must satisfy
this condition:
len
<
ge-value
<
le-value
< 32.
Step 3
ip prefix-list
list-name
seq
seq-value
deny
|
permit
network
/
len
[
ge
ge-value
] [
le
le-value
]
(Optional) Add an entry to a prefix list, and assign a sequence
number to the entry.
Step 4
end
Return to privileged EXEC mode.
Step 5
show ip prefix list
[
detail
|
summary
]
name
[
network
/
len
] [
seq
seq-num
] [
longer
]
[
first-match
]
Verify the configuration by displaying information about a prefix list
or prefix-list entries.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
