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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 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 > 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 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
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