Re: Type-4 LSA and NSSA

I agree with Scott, but look at the following scenario:

Area 0 ------ Area 1

If area 1 has an ASBR and its configured as an NSSA, none of the routers in
the entire domain will see LSA type 4. Whereas,

Area 2 ------ Area 0 ------ Area 1

You will see an LSA type 4 in Area 2.

On Fri, May 8, 2009 at 5:57 PM, Scott Morris <smorris_at_internetworkexpert.com
> wrote:

> 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,
>
> JNCIE-M #153, JNCIS-ER, CISSP, et al.
>
> JNCI-M, JNCI-ER
>
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> Mike Leske wrote:
> > Hi group,
> >
> > can someone please give a hint on this?
> >
> > I have problems to understand why OSPF LSA Type-4 should be allowed
> within
> > NSSA's.
> >
> > According to Routing TCP/IP, Vol. 1, page 389, Type-4 LSA's are allowed
> to
> > be sent into NSSA's.
> > Cisco (
> >
> http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a88.shtml
> )
> > gives a similar description:
> > After you define Area 1 as an NSSA, it must have these characteristics:
> > - No Type 5 LSAs are allowed in Area 1
> >
> > Cisco further defines Type-3 and Type-4 LSA's are not sent into Totally
> > NSSA's.
> >
> > Does it make sense?
> > As we know, LSA Type-4 describe ASBR's; but if the information about
> > external routes is blocked, there's no need to have Type-4 LSA's.
> >
> > When I Lab this up, the NSSA router indeed has NO Type-4 LSA pointing to
> an
> > ASRB within Area 0.
> >
> > Thus, in which scenario will I ever see Type-4 LSA's within a NSSA?
> >
> > Thanks in advance.
> >
> > Mike
> >
> >
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-- 
Narbik Kocharians
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