Prifix list

[devang_etcom]

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

[mheusinger]

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