From: Omkar Tambalkar (omkar.groupstudy@gmail.com)
Date: Thu Oct 23 2008 - 22:36:09 ARST
Amernas, thanks for the link.
I understood the reason behind the problem that was occuring i.e. the second
ABR was seeing 2 equal cost routes to the external route and it preferred
the E2 route to the N2 route but I dont understand that how the suppressing
of the forwarding address on the translator ABR made this router choose the
N2 route.
If I check the LSDB I see that the metrics for the N2 and E2 routes for the
external network are still the same.
Rack1R4#sh ip ospf database external 160.1.60.0
OSPF Router with ID (155.1.4.4) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 228
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 160.1.60.0 (External Network Number )
Advertising Router: 200.200.200.200
LS Seq Number: 80000001
Checksum: 0x950A
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
-------------------------------------------------------------------->
default metric of an E2 route
Forward Address:
0.0.0.0-----------------------------------------------> suppressing the
forwarding address
External Route Tag: 0
Rack1R4#sh ip ospf database nss
Rack1R4#sh ip ospf database nssa-external
OSPF Router with ID (155.1.4.4) (Process ID 1)
Type-7 AS External Link States (Area 1)
Routing Bit Set on this LSA
LS age: 1388
Options: (No TOS-capability, Type 7/5 translation,
DC)---------------------------> does this mean that this LSA is a candidate
for type 7/5 translation?
LS Type: AS External Link
Link State ID: 160.1.60.0 (External Network Number )
Advertising Router: 150.1.6.6
LS Seq Number: 80000003
Checksum: 0xA65
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
------------------------------------------------------------> default metric
for the N2 route
Forward Address: 150.1.6.6 -------------------------------------> as
advertised by the NSSA ASBR
External Route Tag: 0
-Later,
Omkar
On Thu, Oct 23, 2008 at 5:13 PM, amernas <taloust@gmail.com> wrote:
> check this link for more :http://www.cciecandidate.com/?p=333
> Omkar Tambalkar wrote:
>
>> In this lab there are 2 ABRs for the NSSA but lab asks you to hard-code
>> the
>> router-ids on one of the ABRs so that it becomes the router to convert the
>> Type 7 LSA received by the NSSA ASBR in Type 5 LSA to be advertised into
>> area 0.
>> My area 0 router database shows that it is learning the external route by
>> the ABR that was hard-coded to advertise the Type 5 LSA but shows that the
>> route is reachable via both ABRs in the routing table. Why would it
>> install
>> the route from the other ABR when its LSDB does not contain that route as
>> being advertised by that ABR?
>>
>> LSDB section for External routes on Area 0 router:
>> Type-5 AS External Link States
>> Link ID ADV Router Age Seq# Checksum Tag
>> 160.1.50.0 155.1.0.5 1905 0x80000005 0x00E442 0
>> 160.1.60.0 200.200.200.200 129 0x80000004 0x00B642 0
>> ---------------->ABR supposed to advertise the external route
>> Rack1R5#
>>
>> Routing table of Area 0 router:
>> Rack1R5#sh ip route ospf
>> 155.1.0.0/24 is subnetted, 2 subnets
>> O IA 155.1.146.0 [110/74] via 155.1.0.4, 00:32:59, Serial0/0
>> [110/74] via 155.1.0.1, 00:32:59, Serial0/0
>> 160.1.0.0/24 is subnetted, 2 subnets
>> O E2 160.1.60.0 [110/20] via 155.1.0.1, 00:32:59, Serial0/0
>> ----------------------> should be only this route
>> [110/20] via 155.1.0.4, 00:32:59, Serial0/0
>> ----------------------> why are you here also?
>> 150.1.0.0/16 is variably subnetted, 4 subnets, 2 masks
>> O IA 150.1.6.6/32 [110/75] via 155.1.0.4, 00:32:59, Serial0/0
>> [110/75] via 155.1.0.1, 00:32:59, Serial0/0
>> O IA 150.1.4.4/32 [110/65] via 155.1.0.4, 00:32:59, Serial0/0
>> O IA 150.1.1.1/32 [110/65] via 155.1.0.1, 00:32:59, Serial0/0
>>
>> Also the second ABR of the NSSA has the Type 7 LSA received by the ASBR of
>> the NSSA but when it installs the external route in its routing table, it
>> installs it as E2 external route, why does it prefer the E2 route instead
>> of
>> N2 route, is it because the E2 route is coming from the other ABR as a
>> external route via its interface in area 0
>> IP routing table of the second ABR of NSSA:
>> O E2 160.1.60.0 [110/20] via 155.1.146.6, 00:35:07, Ethernet0/0
>> -------------> advertised as E2
>>
>> - Later,
>> Omkar
>>
>>
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>>
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