From: Peter van Oene (pvo@xxxxxxxxxxxx)
Date: Thu Apr 04 2002 - 13:15:37 GMT-3
Most filtering limitations deal with one of two things: a) the requirement
that all routers in the same area maintain identical link state databases
and b) the ability of the ospf implementation to perform the
filtering. As ABR's have to generate type 3's, it is quite possible for
routing vendors to constrain that building process thereby satisfying item
b. Further, filtering type 3's in no way inhibits per area LSDB
synchronization which satisfies a.
Type 3 filtering is quite common as evidenced by the legacy of the
area-range command - summarization generally includes the filtering of more
specific routing information. This new form of filtering simply allows
more control over individual prefix flooding.
Allowing the filtering of type 1/2 LSA's would compromise item a. Also,
the filtering of type 5 LSA's on ABR's would challenge item b (might also
not be entirely in keeping with the standard).
Pete
At 10:33 AM 4/4/2002 -0500, John Neiberger wrote:
>I don't have a way to test this at work.
>Does this actually filter the LSAs from the
>OSPF database? If so, I thought we weren't
>allowed to do that. If we _are_ allowed to
>do this, why not also allow us to use
>distribute-list in with OSPF and ISIS?
>
>Or, does this work similarly to an incoming
>distribute list where it simply stops routes
>from being installed locally but still
>allows the LSA to be propagated?
>
>Thanks,
>John
>
>---- On Thu, 04 Apr 2002, DAN DORTON
>(DHSTS68@dhs.state.il.us) wrote:
>
> > Note that "prefix-list AREA_1" is
>specified.
> >
> > in other words they are using an ip
>prefix-list named AREA_1 to filter
> > type 3 LSAs from area 1.
> >
> > Here is a snip from an example on CCO.
> >
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> > Configuration Examples
> > The following configuration example output
>shows interarea filtering
> > that is applied to both incoming and
>outgoing routes:
> >
> > Router(config)# router ospf 1
> > log-adjacency-changes
> > area 1 filter-list prefix AREA_1_OUT out
> >
> > area 3 filter-list prefix AREA_3_IN in
> >
> > network 10.0.0.0 0.255.255.255 area 3
> > network 172.16.1.0 0.0.0.255 area 0
> > network 192.168.0.0 0.255.255.255 area 1
> > !
> > ip prefix-list AREA_1_OUT seq 10 permit
>10.25.0.0/8 ge 16
> > ip prefix-list AREA_1_OUT seq 20 permit
>172.20.20.0/24
> > !
> > ip prefix-list AREA_3_IN seq 10 permit
>172.31.0.0/16
> >
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> >
> >
> > >>> "peter brown" <pita40@hotmail.com>
>04/04/02 02:30PM >>>
> > I want to know under what situation would
>you use this command in ospf.
> > I
> > know it is used to filter type 3 lsa from
>an area. Also do you need to
> > write
> > an access-list to be referenced. The
>example in CCO did not have an
> > access-list associated with it. The
>command is
> > "area 1 filter-list prefix-list AREA_1"
>in/out
> >
> > Please help
> >
> >
> >
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:57:54 GMT-3