From: Thomas Fowles (tfowles@gmail.com)
Date: Thu Apr 17 2008 - 20:31:53 ART
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
>
>
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