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Dell Configuration Guide for the S4048–ON System 9.14.2.5

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Creating a Prefix List

To create a prefix list, use the following commands.

  1. Create a prefix list and assign it a unique name.
    You are in PREFIX LIST mode.
    CONFIGURATION mode
    ip prefix-list prefix-name
  2. Create a prefix list with a sequence number and a deny or permit action.
    CONFIG-NPREFIXL mode
    seq sequence-number {deny | permit} ip-prefix [ge min-prefix-length] [le max-prefix-length]
    The optional parameters are:
    • ge min-prefix-length: the minimum prefix length to match (from 0 to 32).
    • le max-prefix-length: the maximum prefix length to match (from 0 to 32).

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.

DellEMC(conf-nprefixl)#seq 20 permit 0.0.0.0/0 le 32
DellEMC(conf-nprefixl)#seq 12 deny 134.23.0.0 /16
DellEMC(conf-nprefixl)#seq 15 deny 120.23.14.0 /8 le 16
DellEMC(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
DellEMC(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 Dell EMC Networking OS assign a sequence number based on the order in which the filters are configured. The Dell EMC Networking OS assigns filters in multiples of five.

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