Re: OSPF LSA Type-3 filtering | Single ABR

The important thing to remember is the "generating" abr will always summarise the type 1/2 as a type 3 and into the normal area's so when applying area x filter-list then this would only be applicable if it comes into the area as a type 3 hence the processing is not applicable to your requirement.

OSPF does this for stability purposes hence you technically can't filter a type 3 when the abr is generating and summarising the type 1/2

You could filter the intra-area information at the abr by using area x range x.x.x.x no-advertise this way the information used for the type 3 LSA isn't available and end result is it won't be summarised this would happen for all areas.

The only place where this would not work is if you need the type 3 to reach area x but no other area's the correct solution here would be to use a distribute-list inbound to the new area - this would not filter the type 3 though

Please feel free to correct my understandings, I am reading from my notes.

--
BR
Tony
Sent from my iPad
> On 27 Oct 2013, at 19:28, "1000baseT_at_gmail.com" <1000baset_at_gmail.com> wrote:
> 
> I was wondering if someone can help shed some light on this situation.
> 
> I was practicing various filtering capabilities OSPF with I am came across
> something that doesn't really make sense to me.  It involves filtering
> between areas on the SAME abr.
> 
> 
>                 Area 0
>                   |
> <*R1*> -- area 13 -- <*R3*> -- area 32--  <*R2*>
> Prefix
> 1.1.1.1/32
> 
> This came about when I exploring the direction option (In /. out) with the
> filter-list command.  This following is what I suspect should have worked,
> but it doesn't seem to when both the ABR is the one generating the Type-3
> and is also the ABR doing the filtering...
> 
> Can someone explain why this may be the case...order of operations issue
> maybe?   i.e.  The ABR sends its locally generated Type-3 LSA locally
> before filtering them?
> 
> 
> ip prefix-list R1_FILTER den 1.1.1.1/32
> ip prefix-list R1_FILTER per 0.0.0.0/0 le 32
> !
>  router ospf 1
>     *area 0* filter-list prefix R1_FILTER *out*
> 
> 
> However all three of the following combinations work as expected:
>  router ospf 1
>     area 13 filter-list prefix R1_FILTER out
> -or-
>     area 32 filter-list prefix R1_FILTER in
> -or-
>     area 0 filter-list prefix R1_FILTER in
> 
> thanks
> 
> 
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