Dell Force10 S4810P - Page 124

124 | Access Control Lists (ACLs)
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If you want to forward all routes that do not match the prefix list criteria, you must configure a prefix list
filter to permit all routes (
permit 0.0.0.0/0 le 32). The “permit all” filter should be the last filter in your
prefix list. To permit the default route only, enter
permit 0.0.0.0/0.
The example below illustrates 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.
FTOS(conf-nprefixl)#seq 20 permit 0.0.0.0/0 le 32
FTOS(conf-nprefixl)#seq 12 deny 134.23.0.0 /16
FTOS(conf-nprefixl)#seq 15 deny 120.23.14.0 /8 le 16
FTOS(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
FTOS(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 the PREFIX LIST mode.
If you are creating a standard prefix list with only one or two filters, you can let FTOS assign a sequence
number based on the order in which the filters are configured. The FTOS assigns filters in multiples of
five.
To configure a filter without a specified sequence number, use these commands in the following sequence
starting in the CONFIGURATION mode:
2
seq sequence-number {deny |
permit} ip-prefix [ge
min-prefix-length] [le
max-prefix-length]
CONFIG-NPREFIXL Create a prefix list with a sequence number
and a deny or permit action. 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).
Step Command Syntax Command Mode Purpose
1 ip prefix-list prefix-name CONFIGURATION Create a prefix list and assign it a unique
name.
Step Command Syntax Command Mode Purpose