From: Jared Scrivener (jscrivener@ipexpert.com)
Date: Fri Jan 30 2009 - 13:52:29 ARST
Hey Kelvin,
NSSA Areas assume that the external network being redistributed into OSPF is
going to be the default route out of the NSSA Area for routers in that area.
Normally that is a local internet link for a stub site. Hence we don't use a
Type 3 LSA to 0/0.
A Totally Stubby Area receives only one Type 3 LSA the 0/0 update pointing
to the ABR connecting to Area 0.
If an NSSA is Totally Stubby and it did not have the Type 3 LSA to 0/0
pointing to the ABR, then it would not have received ANY Type 3 LSA - it
would effectively be cutoff from the OSFP network. Instead, a Totally Stubby
NSSA relaxes its logic and assumes that the ABR will be the default route
and that the external routes redistributed into the NSSA area will be
specific only to a set of networks (maybe for an extranet link or something
similar).
Cheers,
Jared Scrivener CCIE3 #16983 (R&S, Security, SP), CISSP
Technical Instructor - IPexpert, Inc.
Telephone: +1.810.326.1444
Fax: +1.810.454.0130
Mailto: jscrivener@ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Kelvin Yeo
Sent: Friday, 30 January 2009 10:42 AM
To: 'Cisco certification'
Subject: NSSA Default route
Hi GS,
RFC spec for NSSA, there is no default generated by default. Default route
is generated for Totally NSSA.
Just curious, why is there such a difference but is not observed in
Stub/Not-so-stub area.
Rgd,
Kelvin
Blogs and organic groups at http://www.ccie.net
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