Configuring Bgp Community Filtering - Cisco WS-CBS3032-DEL Software Configuration Manual

Chapter 39 Configuring IP Unicast Routing
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:
Command
Step 1 configure terminal
Step 2
ip prefix-list list-name [seq seq-value] deny |
permit network/len [ge ge-value] [le le-value]
Step 3 ip prefix-list list-name seq seq-value deny |
permit network/len [ge ge-value] [le le-value]
Step 4 end
Step 5 show ip prefix list [detail | summary] name
[network/len] [seq seq-num] [longer]
[first-match]
Step 6 copy running-config startup-config
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:
•
•
•
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OL-13270-06
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.
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
Purpose
Enter global configuration mode.
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.
(Optional) Add an entry to a prefix list, and assign a sequence
number to the entry.
Return to privileged EXEC mode.
Verify the configuration by displaying information about a prefix list
or prefix-list entries.
(Optional) Save your entries in the configuration file.
Configuring BGP
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