Prifix list

Unanswered Question
Feb 12th, 2007

i want some detail explanation of Prifix list... i want to understand le, ge option... as i know all this but some time getting confuse during the use... so then i have to switch from ip prifix list to access-list... so please provide me some good example with good explanation.

regards

Devang

I have this problem too.
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mheusinger Mon, 02/12/2007 - 10:02

Hi,

prefix-lists are built to describe routing updates. Especially with SPs in BGP they are used. Examples:

Do not accept any route with a mask of /25 or /26 or larger.

ip prefix-list NoNo permit 0.0.0.0/0 le 24

Do only accept a specific subnet from a customer:

ip prefix-list Customer1 permit 172.17.18.0/24

Do allow only subnets up to /18 in Class B address space:

ip prefix-list ClassBsubs permit 128.0.0.0/2 ge 16 le 18

So the first portion X.X.X.X/Y describes the network part of a prefix, the second portion of the prefix-list (ge le) describes the mask of the prefix.

Hope this helps!

Regards, Martin

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