From: daniel.yusuf@nsn.com
Date: Fri Aug 15 2008 - 06:56:27 ART
hello all, actually it is a general question... however, thanks for any
response...
the topology is simply as follow
|------- rD --------|
rA ------| |-------rB
|--------rC---------|
rA - rD - rC in NSSA
rB - rD - rC in backbone.
rA is redistributing static route into OSPF,
while typing sh ip ospf command in both ABR, only rC Perform type-7/type-5 LSA
translation. see the following truncated response.
then i was thinking wether rD is/ is not doing type-7/type-5 translation ??
rD#sh ip osp
Area 1
Number of interfaces in this area is 2
It is a NSSA area
Area has no authentication
SPF algorithm last executed 00:14:26.248 ago
SPF algorithm executed 7 times
Area ranges are
Number of LSA 10. Checksum Sum 0x02BF96
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
rC#sh ip osp
Area 1
Number of interfaces in this area is 2
It is a NSSA area
Perform type-7/type-5 LSA translation
Area has no authentication
SPF algorithm last executed 00:13:51.888 ago
SPF algorithm executed 10 times
Area ranges are
Number of LSA 10. Checksum Sum 0x02BF96
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
________________________________
From: ext Hobbs [mailto:deadheadblues@gmail.com]
Sent: jeudi 14 ao{t 2008 22:01
To: Daniel Valle
Cc: Yusuf Daniel (NSN - MA/Rabat); ccielab@groupstudy.com
Subject: Re: P-bit in NSSA ABR
Daniel (the first one Mr. Yusef), can you post your task and topology? I am
curious to know what is the requirement :)
thanks
On Thu, Aug 14, 2008 at 2:24 PM, Daniel Valle <danielfrvalle@gmail.com>
wrote:
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
>
>
> Blogs and organic groups at http://www.ccie.net
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