From: kasturi cisco (kasturi_cisco@hotmail.com)
Date: Fri Jun 16 2006 - 03:27:37 ART
Hello,
Here is how i look at it. The Are-filter list is for filtering the ABR Type
3 link-state advertisement (LSA). This Filtering feature extends the
capability of an ABR that is running the OSPF protocol to filter type 3 LSAs
between different OSPF areas. This feature allows only specified prefixes to
be sent from one area to another area and restricts all other prefixes. This
type of area filtering can be applied out of a specific OSPF area, into a
specific OSPF area, or into and out of the same OSPF areas at the same time.
>I tried filtering External LSA's between areas with an area filter list but
> >it does not work! I was told that filter lists do not work on External
>LSA's. Is that true? >
To filter External LSA some mechanisms that may be used are: Stub areas,
Totally stubby (filters external+inter-area also) or with
route-summarization with "not-advertise". Wont this work ? Depends on the
scenario u have.
>Also I tried using inbound distribute lists but it seems the External LSA's
>are still being forwarded to the next hop routers and it seems I have to
>use
>distribute lists on all the routers... > >How do you filter External LSA's?
I dont think ditribute-list is an option for OSPF which is a link state
protocol. This is normal behaviour. To filter routes in OSPF we would need
to use this on evey router bcoz the LSA will still get flooded as the OSPF
database have to be similiar across all OSPF areas per link state std. So
route-filtering using distribute list is ONLY an option for DV protocols.
HTH.
Kasturi.
>From: CCIEin2006 <ciscocciein2006@gmail.com>
>Reply-To: CCIEin2006 <ciscocciein2006@gmail.com>
>To: "Cisco certification" <ccielab@groupstudy.com>
>Subject: Not possible to filter External LSA's between areas in OSPF?
>Date: Thu, 15 Jun 2006 11:21:10 -0400
>
>Hello group,
>
>I tried filtering External LSA's between areas with an area filter list but
>it does not work! I was told that filter lists do not work on External
>LSA's. Is that true?
>
>Also I tried using inbound distribute lists but it seems the External LSA's
>are still being forwarded to the next hop routers and it seems I have to
>use
>distribute lists on all the routers...
>
>How do you filter External LSA's?
>
>Thanks.
>
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