Re: Filter subnets - distribute-list and prefix-list

From: George Robbins (grr@shandakor.tharsis.com)
Date: Sat Dec 16 2000 - 10:25:11 EST


Well, prefix lists and distribute lists are mutually exclusive.
You *can* have both a filter list and one of the other two.

I suspect the reason is that prefix-lists are basically an
alternative notation for access-lists and probably end up
hanging on the same hook internally.

If you need something more flexible, then you need to embed that
logic in your route-maps.

You might want to note that there is also a global distribute
in/out that applies to BGP also,

        router bgp 66666
        distribute 111 in
             - or -
        distribute prefix-list xyz in

If you know that you want apply prefix-length limits or martian
filters to *all* of your BGP sessions you can do it there and still
leave your options for per-neighbor lists open.

                                                George

> Date: Sat, 16 Dec 2000 09:33:04 -0500
> From: Brent Sweeny <sweeny@indiana.edu>
> To: "Miguel A.L. Paraz" <map@internet.org.ph>
> Cc: cisco-nsp@puck.nether.net
> Subject: Re: Filter subnets - distribute-list and prefix-list
> Resent-Sender: cisco-nsp-request@puck.nether.net
>
> On Sat, Dec 16, 2000 at 01:52:58PM +0800, Miguel A.L. Paraz wrote:
> > I have put in the distribute-list access-list to block prefixes >= /24.
> > It works great.
> >
> > This is in the 12.1 BGP manual, though:
> >
> > "Note Although neighbor prefix-list can be used as an alternative to the
> > neighbor distribute-list command, do not use attempt to apply both neighbor
> > prefix list and neighbor distribute-list filtering to the same neighbor."
> >
> > I haven't done this, but will it cause major problems?
>
> filter-lists and distribute-lists for neighbors are exclusive. the parser
> won't let you use both; it'll make you remove one to use the other.
> Brent Sweeny, Indiana University
>
>



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