For example: advertise all /24s from OSPF into BGP, but not the /32s. Impossible to do with access lists.
the above statement can be found in this forum, in a question related to the differences between Cisco IOS ACLs and Cisco IOS prefix lists
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Can you link to the original question? It's hard to tell without the context.– Ron TrunkCommented Jun 17, 2016 at 15:44
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1 Answer
You could use ACLs to specifically do this, but you would need an ACL entry for each network, and any network changes would necessitate a change to the ACL.
With a prefix list, you can do every current or future network of a particular size, or range of sizes, with a single line. I think this is the sort of thing that the quote meant, but you haven't provided the source, so I can't see the context.
Update based on comments:
The word, "impossible," seems to be poorly explained. It is impossible to account for every possible case because the ACL would be far too large for any router. What the ACL really can't do, the prefix list can do with a single line.
answered Jun 17, 2016 at 15:45
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I provided the context, please see the link above. I am perplexed by the word impossible used in that statement– MiniMeCommented Jun 17, 2016 at 16:01
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To expand on Ron's answer, a prefix list will allow you to permit any /24 or deny any /32, based on length. With an access list, you would have to explicitly list every network./ Commented Jun 17, 2016 at 16:07
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@MiniMe, the word, "impossible," was poorly chosen or explained. It is impossible to create an ACL that works for every possible case, but a prefix list can do that.– Ron Maupin ♦Commented Jun 17, 2016 at 16:11
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that is why I am perplexed because I do realize that it is possible but tedious. So the answer is "poor choice of wording" .please post that answer and I will selected as correct although I would rather delete this post and correct that response from IOShints, a well known author ..that is what made me question my own understanding rather than his wording– MiniMeCommented Jun 17, 2016 at 16:16
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