From: Imal kalutotage (imal.kalutotage@gmail.com)
Date: Sat Aug 27 2005 - 13:12:17 GMT-3
Hi chris,
As Montiean mentioned, I also experience the same problem..
I went through ur mail 7 also the doc cd.but still I cannot get it right
My setup is like this
R2--------R3---------R4
area 0 area 34
area 34 is configured as nssa.
i am redistributing a loopback from R4.
Then I removed area nssa command from R3 (ABR for area 34)
& put the following command on R3
Then clear the ospf
area 34 nssa translate type7 suppress-fa
But I cannot see any diffrence in the routing table or the ospf database on
R2
It still shows the forwarding address in it's database..
So effectively I am not seeing any affect on this command..
it it a bug or am I missing something here?
Cheers
imal
On 8/25/05, Chris Lewis (chrlewis) <chrlewis@cisco.com> wrote:
>
> Hi,
>
> I think the first step is to understand what the forwarding address is,
> what it is used for and then look at why suppressing it may be
> beneficial.
>
> Starting from the position that NSSA is there to allow the injection of
> external routes from a stub area to the backbone, we know that the NSSA
> area will have type 7 LSAs in it that represent the external prefixes
> being injected. These will be translated at the NSSA ABR to type 5s. The
> NSSA ABR has to tell the backbone routers how to reach these external
> prefixes, so there are two choices, either the NSSA ABR propagates the
> actual address of the router injecting these external routes, or the
> NSSA router sends a default in to the backbone and says contact me to
> get to these external routes and I will take it from there. The address
> of the injecting router or the default, is advertized as the forwarding
> address in the external LSA.
>
> So you end up with two choices. If you propagate all the NSSA routes in
> to the backbone, there is no need to suppress the forwarding address.
> However if you do not advertize all the NSSA internal routes in to the
> backbone, you will need to ensure the forwarding address is suppressed
> as the backbone routers will not know how to get to the injecting
> router.
>
> In either case, the suppress fa command has nothing to do with
> suppressing the routes from the NSSA in to the backbone, you have to
> figure that out separately J but what it does is alter the value of the
> forwarding address in the external LSA.
>
> It is also worth noting the conditions necessary for a router to install
> an external LSA in to the routing table. Basically a router needs to see
> the ASBR (the one injecting the external route of interest) via an intra
> or inter area route AND the forwarding address must be known via an
> intra or inter area route.
>
> In many cases you will see 0.0.0.0 <http://0.0.0.0> as the forwarding
> address already
> with the sho ip ospf database external A.B.C.D command. I recommend you
> try out some configs with your setup to see when you get
0.0.0.0<http://0.0.0.0>or the
> injecting router IP as the forwarding address and that should clear
> things up.
>
> Chris
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Montiean
> Sent: Saturday, August 20, 2005 10:29 PM
> To: ccielab@groupstudy.com
> Subject: nssa translate type7 suppress-fa
>
> Hi,
>
> Someone please explains me about this command "nssa translate type7
> suppress-fa". From cisco
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hi
> rp_c/
> ch15/hoadsup.htm
>
> Per my understanding, forwarding addresses in type7 will be set to
> 0.0.0.0 <http://0.0.0.0> into Type-5 LSAs. I lab it up but couldn't see
> any thing change
> rather than under nssa ABR saying below
>
> Perform type-7/type-5 LSA translation, suppress forwarding
> address
>
> I also found CSCec72160 in mainline 12.3 advise to take off area nssa
> command and put it back in with "nssa translate type7 suppress" But it
> didn't work for me.
>
> My lab setup is r6 ----area0 ----- r4 ---- area147(nssa)
> -------r1-----rip----- r2.
>
> So I redistributed rip into r1 and use suppress-fa at r4. r6 still
> seeing all the addresses advertised from rip.
> I just want to understand why we use this command, cisco page does not
> explains clearly for me or I miss understand some thing. I appreciate
> any feedback on this question.
>
>
> --Montiean
>
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