Priscilla,
Good point! In his example Doyle also shows that with the use of
the;
area X no-redistribution "no-summary"
the no-redistribution blocks the type 7 LSA's from being sent into the NSSA
which will also cause area 2 to loose it route to network 172.16.x.x.
However with the addition of the "no-summary" command it allows for a type 3
LSA to advertise the default route therefore allowing access to all external
networks without area 2's router having a route in it Routing Information
Base(RIB).
Nigel
>From: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>Reply-To: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>To: "Luobin Yang" <[EMAIL PROTECTED]>, [EMAIL PROTECTED]
>Subject: Re: Why External type 5 LSA is distributed to a totally stubby
>area ?
>Date: Tue, 12 Sep 2000 17:01:30 -0700
>
>At 06:33 PM 9/12/00, Luobin Yang wrote:
>>Dear Priscilla,
>>
>>Thanks for your reply. I do have a copy of Routing TCP/IP. I am not sure,
>>but I think by using the command "area 2 nssa no-redistribution" , we can
>>turn off the P-bit.
>
>But wouldn't that cause other routers in area 2 to lose their route to
>172.16.30.0? The case studies in the OSPF chapter talk more about this
>issue. Unfortunately, they don't use quite the same topology as you are
>using, but perhaps you can translate what they say to your topology.
>
>>But my question is that why in a totally stubby area, there exists
>>situations that External routes could be flooded into? Totally stubby area
>>should block type 3, type 4 and type 5 LSAS.
>
>I can't say why. I think you would have to talk to the OSPF protocol
>designers. They must have thought there was some good reason for it or they
>wouldn't have invented the P-bit. Where are Howard and Pamela when we need
>them? Actually, I know that Howard is at the RIPE and European Operators
>Forum....
>
>Priscilla
>
>
>>Luobin Yang
>>
>>>From: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>>>To: luobin Yang <[EMAIL PROTECTED]>,[EMAIL PROTECTED]
>>>Subject: Re: Why External type 5 LSA is distributed to a totally stubby
>>>area ?
>>>Date: Tue, 12 Sep 2000 16:18:57 -0700
>>>
>>>Do you have a copy of Doyle's Routing TCP/IP book by any chance? If yes,
>>>check out the discussion on page 483 and Figure 9.42. The Figure looks
>>>just
>>>like what you are describing. The discussion says:
>>>
>>>"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."
>>>
>>>Sounds like your P-bit is set! That can be a dangerous thing if you are
>>>not
>>>so stubby. &;-) Seriously, hopefully this is a start for figuring out
>>>what's going on. I'm going to try to find out if there's any
>>>configuration
>>>parameters related to this P-bit and get back to you if I find anything,
>>>or
>>>maybe somebody else knows.
>>>
>>>Priscilla
>>>
>>>At 03:55 PM 9/12/00, luobin Yang wrote:
>>>>Dear group,
>>>>
>>>>I have such a scenerio:
>>>>
>>>>RouterB is connected to RouterA using Serial 0, RouterC is connected to
>>>>RouterA using Serial 1. Interface E0 of Router A is configured as Area
>>>>0, Serial0(to RouterC) of RouterA is configured as Area 2 (nssa area) ,
>>>>Serial1(to RouterB) of RouterA is configured as Area 1 (totally stubby
>>>>area ).
>>>>
>>>>On routerC, I configured OSPF and EIGRP, Serial 1(to RouterA) is running
>>>>OSPF and belongs to area 2 which is a NSSA. E0 is running EIGRP. If I
>>>>redistribute network of E0 ( for example 172.16.30.0 ) from EIGRP to
>>>>OSPF, I found 172.16.30.0 is redistributed to Area 1 which is a totally
>>>>stubby area.
>>>>
>>>>Does anybody know the reason why?
>>>>
>>>>Thanks a lot!
>>>>Luobin
>>>>
>>>>**NOTE: New CCNA/CCDA List has been formed. For more information go to
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>>>
>>>
>>>________________________
>>>
>>>Priscilla Oppenheimer
>>>http://www.priscilla.com
>>
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>
>
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
>
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