Re: Type-4 LSA and NSSA

Yes, you are right and I agree with you - as I already wrote in a previous
post.
R2 will generate a Type-4 LSA into Area 2, because R4 is acting as the ASBR
by converting Type7-to-5.

However, if Area 2 is NSSA, too, R2 will not send a Type-4 LSA into Area 2.

And thats the point where I can confirm that Cisco does meet the RFC, as it
does not forward Type-4 LSAs into NSSAs :-)
Additionally, the table in Routing TCP/IP is not correct.

While my question was only related to NSSAs, you concentrated to explain the
Type-4 flooding outside NSSAs. :-)

Cheers
Mike

2009/5/9 Narbik Kocharians <narbikk_at_gmail.com>

> guys, you can't totally depend on RFCs, you have to see how Cisco
> implemented the RFC.
>
> Here:
>
> Lets say you have the following topology:
>
> R2----R3-----R4-----R5
> The links are all Frame-relay P2P
>
> R2's connection to R3 and R3's connection to R4 are in area 0
> R4's connection to R5 and R5's connection to R4 are in area 1
>
> If R5 redistributes a route. Area 1 routers will NOT see an LSA type 4. But
> the ABR of area 1 will generate an LSA type 4 and it will flood it into area
> 0, as a result of that if a "Show ip ospf da asbr-summ" command is entered
> on R2 or R3, you should see the LSA type 4 being injected by R4, the output
> of the display will show R5 as the ASBR (Link state ID) and the advertising
> router will be the ABR which is R4.
> Now...
> If area 1 is changed into an NSSA area, R4 translates LSA type 7s into LSA
> type 5s, correct?
>
> Therefore, area 0 routers will NOT see an LSA type 4, because now R4
> behaves like an ASBR, (Please dont twist words around). i said it BEHAVES
> like one. Therefore area 0 routers will NOT see an LSA type 4.
>
> Now, let's take this one step deeper and add R1 to R2 and let's run that
> connection in OSPF area 2.
>
> Now R2 is an ABR, it sees LSA type 5s being generated in its own area, so
> what does it do? it generates LSA type 4s, and as a result of that the
> routers in area 2 will see LSA type 4s.
> On Sat, May 9, 2009 at 5:35 AM, Scott Morris <
> smorris_at_internetworkexpert.com> wrote:
>
>> Ahhhh... The RFC's! Definitely the best answer to the question! :)
>>
>>
>>
>>
>> *Scott Morris*, CCIE*x4* (R&S/ISP-Dial/Security/Service Provider) #4713,
>>
>> JNCIE-M #153, JNCIS-ER, CISSP, et al.
>>
>> JNCI-M, JNCI-ER
>>
>> smorris_at_internetworkexpert.com
>>
>>
>> Internetwork Expert, Inc.
>>
>> http://www.InternetworkExpert.com <http://www.internetworkexpert.com/>
>>
>> Toll Free: 877-224-8987
>>
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>>
>>
>> Knowledge is power.
>>
>> Power corrupts.
>>
>> Study hard and be Eeeeviiiil......
>>
>>
>>
>> Mike Leske wrote:
>>
>> Thanks Scott and Narbik for confirming my thoughts.
>>
>> I think I finally found an "official" confirmation for that.
>>
>> RFC 1587 The OSPF NSSA Option states on page 5:
>> "Type-7 LSAs are only flooded within the NSSA. The flooding of type-7 LSAs
>> follow the same rules as the flooding of type 1-4 LSAs."
>> But it describes at no point, that Type-4 LSAs will not be flooded into
>> NSSAs.
>>
>>
>> However, RFC 3101 The OSPF Not-So-Stubby Area (NSSA) Option, which obsoletes
>> RFC 1587, clearly states on page 5:
>> "Since Type-5 AS-external-LSAs are not flooded into NSSAs, NSSA border
>> routers should not originate Type-4 summary-LSAs into their NSSAs."
>>
>>
>> Cheers
>> Mike
>>
>>
>> 2009/5/9 Scott Morris <smorris_at_internetworkexpert.com> <smorris_at_internetworkexpert.com>
>>
>> Type 4's are used for next hop reachability to get to the Type 5 LSAs
>> (ASBR). If you have no Type 5's, you have zero need for a Type 4 LSA. :)
>>
>> So I'd suggest that someone messed up in the book?
>>
>> *Scott Morris*, CCIE*x4* (R&S/ISP-Dial/Security/Service Provider) #4713
>>
>>
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>>
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>>
>>
>>
>>
>
>
> --
> Narbik Kocharians
> CCSI#30832, CCIE# 12410 (R&S, SP, Security)
> www.MicronicsTraining.com
> www.Net-Workbooks.com
> Sr. Technical Instructor

Blogs and organic groups at http://www.ccie.net
Received on Sat May 09 2009 - 17:54:38 ART