access-list query

Answered Question
Oct 27th, 2009
User Badges:

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 9 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.



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
Loading.
Amit Singh Tue, 10/27/2009 - 02:35
User Badges:
  • Cisco Employee,

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
User Badges:

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
User Badges:
  • Cisco Employee,

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.



Actions

This Discussion