From: Thomas Fowles (tfowles@gmail.com)
Date: Fri Apr 18 2008 - 15:03:57 ART
RFC3101 goes into lots of gory detail about the NSSA translation process
(section 3.2 in particular).
http://www.ietf.org/rfc/rfc3101.txt
Caution: prolonged RFC exposure could cause brain hemorrhaging.
HTH
-Tom
CCIE#18762
On Fri, Apr 18, 2008 at 1:55 PM, Thomas Fowles <tfowles@gmail.com> wrote:
> 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
> > > >
> > > > _______________________________________________________________________
> > > > Subscription information may be found at:
> > > > http://www.groupstudy.com/list/CCIELab.html
Pass the CCIE in six weeks, Guaranteed!
http://www.certscience.com/CCIE
This archive was generated by hypermail 2.1.4 : Thu May 01 2008 - 08:25:51 ART