From: Daniel Valle (danielfrvalle@gmail.com)
Date: Thu Aug 14 2008 - 17:24:57 ART
I think the correct question maybe is (Daniel, please correct me I'm
wrong!)... How not to convert LSA type-7 to type-5 because by default it is
converted. The P bit is set to one.
I had the same doubt a couple of years ago.
Let me see if this helps. From Jeff Doyle's book:
"The NSSA External LSA has a flag in its header known as the P-bit. The NSSA
ASBR has the option of setting or clearing the P-bit. If the NSSA's ABR
receives a type 7 LSA with the P-bit set to one, it will translate the type
7 LSA into a type 5 LSA and flood it throughout the other areas. If the
P-bit is set to zero, no translation will take place and the destination in
the type 7 LSA will not be advertised outside of the NSSA. This option
allows you to design an NSSA in which the external destinations learned in
that area are known only in that area."
I got a bit confused with the explanation above because the IOS has the
command: "area x nssa no-redistribute".
This command only works when the router is altogether an ASBR, ABR, and is
connected to a NSSA area AND area zero
the diagram below illustrates an example where the "area x nssa
no-redistribute" does not make any filtering to avoid the RIP route comming
to area 0.
(RIP)<--R1-->(OSPF NSSA AREA)<--R2-->(OSPF AREA 0)<--R3
You cannot filter at R2 the LSA Type-7 which was generated by R1. the only
way to do it would be ( from the book troubleshooting ip routing protocols):
"summary-address x.x.x.x x.x.x.x not-advertise
This summary-address configuration generates a Type 7 LSA that won't be
translated into a Type 5 LSA by the NSSA ABR.
"
It would only work in this topology: R2 redistributing the RIP routes to
area 0 and not to nssa area
*(RIP)*
|
R1-->(OSPF NSSA AREA)<--R2-->(OSPF AREA 0)<--R3
Configure the no-redistribution command on an NSSA ABR that's also an ASBR.
( R2 in the example)
Hope this helps,
Daniel Valle
On 8/13/08, Scott Morris <smorris@internetworkexpert.com> wrote:
>
> Are you asking in general, or for a particular lab assignment?
>
> "Manually", I'd say that you'll be sitting by a router looking to change
> things in packets, but that's time consuming and detailed work that nobody
> wants. :)
>
> First ask what is the P-bit? Then you may find the answer leaps out a
> little when looking at a few commands.
>
> But a little more context to your question may help me give a better answer
> to you! (Check out RFC 3101)
>
> HTH,
>
>
> Scott Morris, CCIE4 #4713, JNCIE-M #153, JNCIS-ER, CISSP, et al.
> CCSI/JNCI-M/JNCI-ER
> Senior CCIE Instructor
>
> smorris@internetworkexpert.com
>
>
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com <http://www.internetworkexpert.com/>
> Toll Free: 877-224-8987
> Outside US: 775-826-4344
>
> Knowledge is power.
> Power corrupts.
> Study hard and be Eeeeviiiil......
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> daniel.yusuf@nsn.com
> Sent: Wednesday, August 13, 2008 11:42 AM
> To: ccielab@groupstudy.com
> Subject: P-bit in NSSA ABR
>
> Hi GS,
>
> How to change P-bit in LSA type-7 at NSSA ABR manually... ?
>
> Thanks for your response,
>
> -daniel
>
>
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