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Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 35 Configuring IP Unicast Routing
Configuring BGP
You do not need to specify a sequence number when removing a configuration entry.
Show
commands
include the sequence numbers in their output.
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 of 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 based on the value of the
COMMUNITIES attribute. The attribute is a way to groups destinations into communities and to apply
routing decisions based on the communities. This method simplifies 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. AS 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.
