From: Roman Rodichev (rodic000@xxxxxxxxxxx)
Date: Sat Jun 02 2001 - 12:19:05 GMT-3
Actually. That's right, it depends on what you mean Darren. Is "better"
longer or shorter? "Better" could be a more specific route. But "Better"
could be a larger summary. It's just I can't find a reson why you would want
to get >/19 routes. ISPs usually want larger summaries. That's why this
should be correct:
access-list 100 permit ip 0.0.0.0 255.255.224.0 255.255.224.0 225.255.224.0
You basically want the least significant 13 bits (last 13 bits) of the mask
to be 0's. So these masks would match:
255.255.224.0
255.255.192.0
255.255.128.0 and so on...
But this one wouldn't: 255.255.240.0
my 2 cents
>From: "Bob Chahal" <bob.chahal@ntlworld.com>
>Reply-To: "Bob Chahal" <bob.chahal@ntlworld.com>
>To: "Darren Ward" <dward@pla.net.au>, <ccielab@groupstudy.com>
>Subject: Re: Match prefixes gt using access-list?
>Date: Sat, 2 Jun 2001 12:35:09 +0100
>
>No sure what you mean by better but if you want to filter /19 or longer
>prefixes from a neighbor
>
>then
>
>access-list 101 deny ip 0.0.0.0 255.255.255.255 255.255.224.0 0.0.31.255
>access-list 101 permit ip any any
>
>router bgp xx
>neighb y.y.y.y remote zz
>neighb distribute-list 101 in
>
>
>
>----- Original Message -----
>From: "Darren Ward" <dward@pla.net.au>
>To: <ccielab@groupstudy.com>
>Sent: Saturday, June 02, 2001 11:16 AM
>Subject: BGP: Match prefixes gt using access-list?
>
>
> > Hi All,
> >
> > I've ben asked a damn good question by a co-worker and I must admit I'm
> > not exactly sure how to solve it.
> >
> > Q: Filter BGP advertisements to a neighbour so that only routes that are
> > /19 or better are advertised WITHOUT using a prefix-list.
> >
> > A:
> >
> > I know it will be a BGP extended IP access-list using the network/mask
> > pair but can't figure out the mask section properly.
> >
> > access-list 100 permit ip 0.0.0.0 255.255.224.0 255.255.224.0
> > 225.255.224.0
> >
> > Now, I _think_ this means match ANY network where the last 13 bits are
> > all zero AND the last 13 bits of the netmask are all zeros but allow
> > more zeros the base 13 bits (greater than /19)
> >
> > Is this correct?
> >
> > Darren Ward
> > (Sydney June 27-28)
> > **Please read:http://www.groupstudy.com/list/posting.html
>**Please read:http://www.groupstudy.com/list/posting.html
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