a couple of quick thoughts: ""Joep Hoet"" wrote in message news:[EMAIL PROTECTED].; > From the BGP section in the BSCN course book I "understand" that > IP-Prefixlist are essentially nothing but another method of reaching the > same goal as a distribute-list, but with a better performance and a more > convenient user-interface.
sure, that's one way of looking at it. make it easier for the folks at the ISP's to do their job. > So they are (except for performance) functional the same, and there > would be no reason to use a distribute-list instead of a ip prefix list ever. > think of distribute list as a sledge hammer and prefix list as a hammer and chisel. You can attempt sculpture with both. one will get you different and finer results than the other. > I wonder whether this is also true in regards to on which interfaces they > work on. > > Are IP-Prefix-lists indeed only used on incoming packets: so do they filter > on incoming routes only? nope - in and out by neighbor R8(config-router)#neigh 1.1.1.1 prefix-list qwerty ? in Filter incoming updates out Filter outgoing updates > > So, is it true than that IP-Prefix-lists are for filtering incoming updates, > and distribute-lists (I'm talking BGP only) are able to filter both on > incoming and outgoing packets? yep > > If so, is the matter of "better performance" for IP-prefix-list partly > caused the fact that you don't hassle you router with packets you can kill > on your incoming interface, which you can do with a outbound distribute-list > route filtering? > interesting question. my own ( ignorant ) opinion is that at this point it comes down to the way a router/computer operates. I think the boolean operation used against a prefix list is probably faster and less resource intesive than a similar operation against a distribute list. why? If pushed I would guess it has to do with the legacy coed in the IOS versus the new code written around prefix lists. Cisco has some pretty sharp computer science geeks running their code development. consider that in order to filter so that I get just those routes with a 15 bit prefix, what I would have to do with a distribute list, versus what I would have to do with a prefix list. the distribute list requires a reference to an access list, which means an exra operation or two for each line. a prefix list cab be operated on with just the one operation per line. > Plz explain presumming only BGP knowledge at the BSCN/CCNP level. > > Thnx, > Joep Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37065&t=37059 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
