Re: Type-4 LSA and NSSA

Yes.... your brain stills seems to have enough synapses in the up/up state
:-)
I was talking about LSA Type 4's into NSSAs.

The Cisco documents are somewhat inconsistent, but the SupportWiki site
states what I saw here:
http://supportwiki.cisco.com/ViewWiki/index.php/How_to_configure_OSPF_NSSA

" NSSAs block type 4 and 5 LSAs. NSSA totally stub area blocks type 3, 4,
and 5 LSAs. "

Mike

2009/5/9 Scott Morris <smorris_at_internetworkexpert.com>

> It may be that my brain is shutting down for the weekend... But I would
> classify these examples as expected behavior. I think the behavior in
> question was talking about LSA Type 4's going the other way... The INTO
> stub/NSSA areas.
>
> At least that was what I read yesterday, when I presume my brain was still
> working. If not, please let me know, but otherwise you are making me shake
> dust off. :)
>
>
>
>
> *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
>
> Toll Free: 877-224-8987
>
> Outside US: 775-826-4344
>
>
> Knowledge is power.
>
> Power corrupts.
>
> Study hard and be Eeeeviiiil......
>
>
>
>
> Narbik Kocharians wrote:
>
> 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/> <http://www.internetworkexpert.com/>
>
> Toll Free: 877-224-8987
>
> Outside US: 775-826-4344
>
>
> 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> <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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Received on Sat May 09 2009 - 21:02:10 ART