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Example of Assigning Sequence Numbers to Filters
If you want to forward all routes that do not match the prefix list criteria, configure a prefix list filter to
permit all routes (permit 0.0.0.0/0 le 32). The “permit all” filter must be the last filter in your prefix
list. To permit the default route only, enter permit 0.0.0.0/0.
The following example shows how the seq command orders the filters according to the sequence
number assigned. In the example, filter 20 was configured before filter 15 and 12, but the show config
command displays the filters in the correct order.
Dell(conf-nprefixl)#seq 20 permit 0.0.0.0/0 le 32
Dell(conf-nprefixl)#seq 12 deny 134.23.0.0 /16
Dell(conf-nprefixl)#seq 15 deny 120.23.14.0 /8 le 16
Dell(conf-nprefixl)#show config
!
ip prefix-list juba
seq 12 deny 134.23.0.0/16
seq 15 deny 120.0.0.0/8 le 16
seq 20 permit 0.0.0.0/0 le 32
Dell(conf-nprefixl)#
NOTE: The last line in the prefix list Juba contains a “permit all” statement. By including this line in a
prefix list, you specify that all routes not matching any criteria in the prefix list are forwarded.
To delete a filter, use the no seq sequence-number command in PREFIX LIST mode.
If you are creating a standard prefix list with only one or two filters, you can let the system assign a
sequence number based on the order in which the filters are configured. The system assigns filters in
multiples of five.
Creating a Prefix List Without a Sequence Number
To create a filter without a specified sequence number, use the following commands.
1. Create a prefix list and assign it a unique name.
CONFIGURATION mode
ip prefix-list prefix-name
2. Create a prefix list filter with a deny or permit action.
CONFIG-NPREFIXL mode
{deny | permit} ip-prefix [ge min-prefix-length] [le max-prefix-length]
The optional parameters are:
• ge min-prefix-length: is the minimum prefix length to be matched (0 to 32).
• le max-prefix-length: is the maximum prefix length to be matched (0 to 32).
Example of Creating a Filter with System-Assigned Sequence Numbers
The example shows a prefix list in which the sequence numbers were assigned by the software. The filters
were assigned sequence numbers based on the order in which they were configured (for example, the
first filter was given the lowest sequence number). The show config command in PREFIX LIST mode
displays the two filters with the sequence numbers 5 and 10.
Dell(conf-nprefixl)#permit 123.23.0.0 /16
Dell(conf-nprefixl)#deny 133.24.56.0 /8
110
Access Control Lists (ACLs)