Re: Type-4 LSA and NSSA

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

smorris_at_internetworkexpert.com

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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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Received on Fri May 08 2009 - 20:57:20 ART