Re: Type-4 LSA and NSSA

hahahahahaha

Unbelievable, Scott is shaking it again (I mean the dust) JK.......

On Sat, May 9, 2009 at 12:02 PM, Mike Leske <mike.leske_at_googlemail.com>wrote:

> 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 <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/> <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
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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>

-- 
Narbik Kocharians
CCSI#30832, CCIE# 12410 (R&S, SP, Security)
www.MicronicsTraining.com
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