860
Configuring IP Unicast Routing
Configuring BGP
Before using a prefix list in a command, you must set up the prefix list.
BEFORE YOU BEGIN
Enable BGP routing as described in the Enabling BGP Routing, page 850.
DETAILED STEPS
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.
EXAMPLE
In the following example, a prefix list is configured to deny the default route 0.0.0.0/0:
Switch(config)# ip prefix-list RED deny 0.0.0.0/0
In the following example, a prefix list is configured to permit traffic from the 172.16.1.0/24 subnet:
Switch(config)# ip prefix-list BLUE permit 172.16.1.0/24
In the following example, a prefix list is configured to permit routes from the 10.0.0.0/8 network that have a mask length
that is less than or equal to 24 bits:
Switch(config)# ip prefix-list YELLOW permit 10.0.0.0/8 le 24
In the following example, a prefix list is configured to deny routes from the 10.0.0.0/8 network that have a mask length
that is greater than or equal to 25 bits:
Switch(config)# ip prefix-list PINK deny 10.0.0.0/8 ge 25
Command Purpose
1. configure terminal Enter global configuration mode.
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
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.
4. end Return to privileged EXEC mode.
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.
6. copy running-config startup-config (Optional) Save your entries in the configuration file.
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