From: Thomas Fowles (tfowles@gmail.com)
Date: Fri Apr 18 2008 - 14:55:49 ART
Suryakant,
I think that's a bit of a chicken-or-the-egg type thing (which came
first?...). Router A generates the E2 for the benefit of others (area 0)
and sets itself as the advertising router, however, being the translator, it
will prefer the original route (it won't advertise a route to itself).
Similarly (although a bit different), if you 'show ip ospf database' on
router C, you will see the type 7 LSA in the database, but router C will
never install it in its own routing table.
-Tom CCIE#18762
On Fri, Apr 18, 2008 at 10:34 AM, Suryakant P <suryakant.pandian@gmail.com>
wrote:
> Hi Thomas,
>
> In scenario 1 , Going by your explanation,the same logic should be used by
> router A,isnt it?
>
> But router A installs the N2 route in the routing table instead of the E2
> route.
>
> Does router A being the Type 7 - Type 5 converter could make
> the difference here ?Or is it something else?
>
> Thanks
> With regards
> Suryakant
>
>
>
>
> On 4/18/08, Thomas Fowles <tfowles@gmail.com> wrote:
> >
> > Suryakant,
> >
> > In Scenario 1, both the N2 and E2 routes presumably have the same
> > characteristics (forwarding address of router C, cost, etc). All things
> > being equal, an E2 is preferred over an N2 route. So router B installs the
> > E2 advertised by router A into area 0.
> >
> > In Scenario 2, when router A strips out the forwarding address, router
> > A's area 0 interface becomes the next hop for the E2 route. At this point
> > (judging from your sesults) the N2 route with router C as the next hop
> > becomes more attractive than router A's area 0 interface as next hop.
> >
> > Here are a couple of documentation links that might clarify things a
> > bit, although admitedly this can be a tough one to wrap your head around.
> >
> >
> > http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080124c7d.shtml
> >
> > http://www.cisco.com/en/US/docs/ios/12_4/ip_route/configuration/guide/hoadsup.html#wp1037600
> >
> > HTH
> >
> > -Tom
> > CCIE#18762(R&S, SP in progress, humbled daily)
> >
> >
> >
> > On Thu, Apr 17, 2008 at 8:32 AM, Suryakant P <
> > suryakant.pandian@gmail.com> wrote:
> >
> > > Hi All,
> > >
> > > Routers A ,B and C are connected to the ethernet LAN network.OSPF
> > > peering is
> > > established between them and the area is configured as the NSSA area.
> > >
> > > Router C acts as the ASBR and Routers A and B have connectivity
> > > to Area 0 and hence act as ABRs.
> > >
> > > I have made the router A as the type 7 to type 5 converter(by
> > > increasing the
> > > router-id on the A).
> > >
> > > Now when C advertises a network(by redistributing into OSPF),both
> > > router A
> > > and B receive the TYPE 7 LSA.
> > >
> > > A and B will have the TYPE 5 LSA generated by the router A.
> > >
> > > *Scenario 1 :* When the forwardaddress in TYPE 5 LSA is set to Router
> > > C
> > > router id.
> > > Router A installs N2 route in the routing table but router B installs
> > > E2
> > > route in the routing table?Could you please explain the reason behind
> > > the
> > > selection of E2 route on the router B.
> > >
> > > *Scenario 2 :* When the forwardaddress in TYPE 5 LSA is set to
> > > 0.0.0.0(suppress-fa configured on the converter)
> > > Both router A and router B install N2 route to the network
> > > advertised.Could
> > > you please explain the reason behind the change in route selection
> > > once the
> > > forward has been suppressed.
> > >
> > > Thanks
> > > With regards
> > > Suryakant
> > >
> > >
> > > Pass the CCIE in six weeks, Guaranteed!
> > > http://www.certscience.com/CCIE
> > >
> > > _______________________________________________________________________
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