access-list query

Answered Question
Oct 27th, 2009

hello,

i have matched some bgp routes with prefix-list and set local higher local pref for some destination prefixes but same i am getting output when i am matching same routes with standard access-list then why should i use confusing or complex prefix-list? what the exact use of it? and when?

thanks and regards,

sourabh

Correct Answer by Amit Singh about 7 years 3 months ago

Lets take an example :

You need to permit 150.5.x.x network an only which has a default class B subnet mask and allow on the routes which have grtaer than 28 bit mask.

ip prefix-list abc permit 150.50.0.0/16 ge 28

With prefix-list above only the masks which are greater than 28 will be selected.

You wont be able to match it with an ACL.

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Amit Singh Tue, 10/27/2009 - 02:35

Prefix-list with BGP is used for more granular filtering of the routes.

With ACL's you can only match the networks, while with prefix-list you can match on both network + mask.

HTH,

-amit singh

sourabh1000_2 Tue, 10/27/2009 - 02:48

hello Mr.Amit,

But for mask we can use wildcard mask with standard or extended access-list to match the mask of network, am i right? pls suggest.

Thanks and regards

sourabh

Correct Answer
Amit Singh Tue, 10/27/2009 - 03:49

Lets take an example :

You need to permit 150.5.x.x network an only which has a default class B subnet mask and allow on the routes which have grtaer than 28 bit mask.

ip prefix-list abc permit 150.50.0.0/16 ge 28

With prefix-list above only the masks which are greater than 28 will be selected.

You wont be able to match it with an ACL.

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