From: Luan Nguyen (luan.m.nguyen@gmail.com)
Date: Fri Jan 04 2008 - 13:29:31 ARST
Thanks everyone for helping. Especially Narbik for the material!
I learned quite a bit.
I learned that i need to read better. Learned about area range
not-advertise, area filter-list, use more specific show command like show ip
ospf database x.x.x.x to get more detail...etc.
-lmn
On Jan 4, 2008 6:33 AM, Paul Cosgrove <paul.cosgrove@heanet.ie> wrote:
> A NSSA ASBR creates a type-7 external LSA and sets the forwarding
> address. Unlike with other areas ASBRs which only sometimes set this
> value, an NSSA ASBRs will always set it.
>
> The NSSA ABR then translates this type-7 LSA into a type-5. While it
> will specify itself as the advertising router in the type-5, it includes
> the same forwarding address that it received in the ASBRs type-7 LSA.
>
> Routers in different area which receiving the type-5, will check to see
> that the forwarding address is accessible via an inter area route. They
> will only use the LSA if such a route is found, otherwise it is ignored.
>
> If you have a requirement to suppress type-1 and type-2 LSAs from your
> NSSA area into other areas, then you may use area range with the
> not-advertise option to filter the unwanted routes. This is the example
> given on the cisco link you mentioned but filtering using an area
> filter-list or distribute-list etc. can also cause the same issue.
>
> The problem occurs when the route to the forwarding address IP of the
> translated type-5 is filtered out, so it no longer advertised into other
> areas.
>
> When a receiving router checks the type-5 forwarding address and find it
> has no route to that IP, it sees the advertised route as inaccessible
> and ignores the type-5 LSA.
>
> If you set the ABR to override the ASBRs forwarding address and instead
> specify itself in the forwarding address field (actually using 0.0.0.0
> in its advertisement, which is understood to mean itself), then the
> other routers will still accept the type-5.
>
> Paul.
>
> Luan Nguyen wrote:
> > Can I look at the workbook also? :)
> > Would someone kind enough to explain this? I found this:
> >
> http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a00804556e5.html
> > but I don't see any different with that area XX nssa translate type7
> > suppress-fa command. By default, the NSSA ABR already used itself to
> > advertise those type5-translated-from-type7 LSA to its neighbors. What
> is
> > the deal here?
> >
> > -lmn
> >
> > On Jan 3, 2008 8:21 PM, Narbik Kocharians <narbikk@gmail.com> wrote:
> >
> >> Look at the last lab in your OSPF section. From the work book in the
> class
> >> room.
> >>
> >> On 1/3/08, Chris Riling <criling@gmail.com> wrote:
> >>> Hi Group,
> >>>
> >>> Does anyone have a good explanation for "area nssa translate"?
> Frome
> >>> the DocCD:
> >>>
> >>> area nssa translate
> >>>
> >>> To configure an area as a not-so-stubby area (NSSA) and configure the
> >> Open
> >>> Shortest Path First (OSPF) Forwarding Address Suppression in
> Translated
> >>> Type-5 LSAs feature, use the *area nssa translate *command in router
> >>> configuration mode. To remove the NSSA distinction from the area, use
> >> the
> >>> *
> >>> no* form of this command.
> >>>
> >>> *area* *area-id* *nssa* *translate type7 suppress-fa *
> >>>
> >>> no *area* *area-id* *nssa* *translate type7 suppress-fa *
> >>> Syntax Description
> >>>
> >>> *area-id*
> >>>
> >>> Identifier of the area for which authentication is to be enabled. The
> >>> identifier can be specified as either a decimal value or an IP
> address.
> >>>
> >>> *translate*
> >>>
> >>> Translates one type of LSA to another type of LSA. This keyword takes
> >>> effect
> >>> only on an NSSA area border router (ABR) or NSSA Autonomous System
> >>> Boundary
> >>> Router (ASBR).
> >>>
> >>> *type7*
> >>>
> >>> Translates a Type-7 LSA to a Type-5 LSA. This keyword takes effect
> only
> >> on
> >>> an NSSA ABR or an NSSA ASBR.
> >>>
> >>> *suppress-fa*
> >>>
> >>> Suppresses the forwarding address of the Type-7 LSAs from being placed
> >> in
> >>> the Type-5 LSAs. This keyword takes effect only on an NSSA ABR or an
> >> NSSA
> >>> ASBR.
> >>>
> >>> Doesn't an NSSA ABR do this by it's very nature? Also, could someone
> >>> clarify
> >>> when you might use forward address supression?
> >>>
> >>> Thanks,
> >>> Chris
> >>>
> >>>
> _______________________________________________________________________
> >>> Subscription information may be found at:
> >>> http://www.groupstudy.com/list/CCIELab.html
> >>>
> >>
> >>
> >> --
> >> Narbik Kocharians
> >> CCIE# 12410 (R&S, SP, Security)
> >> CCSI# 30832
> >> www.MicronicsTraining.com
> >> Sr. Technical Instructor
> >> www.Net-WorkBooks.com
> >>
> >> _______________________________________________________________________
> >> Subscription information may be found at:
> >> http://www.groupstudy.com/list/CCIELab.html
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
> >
>
>
> --
> Paul Cosgrove
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