ospf duplicate interface address

[Mahesh Gohil]

Hello,

Configured GNS with two routers connected back to back with Gig interface.

Want to know how does they (ospf) detect this duplicate address.

Run some debug but both routers send hello and stay silent.

R1-10.10.10.1-----10.10.10.1--R2

R1 router-id: 1.1.1.1

R2 router-id : 2.2.2.2

Any clue?

Regards # Mahesh

[InayathUlla Sharieff]

Tested physicall devices and that sends out the duplicate address msg.

Tested on Cisco Packet tracer and I found duplicate msg:

R1--F0/0----f0/0--R2

Router(config)#int f0/0
Router(config-if)#ip address 10.10.10.1 255.255.255.0
Router(config-if)#
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
%IP-4-DUPADDR: Duplicate address 10.10.10.1 on FastEthernet0/0, sourced by 0001.9786.6601

Router#

Could be issue with GNS.

HTH

[Mahesh Gohil]

Sorry ! I was looking for how OSPF detect this. Logically OSPF should struct in Exstart state or no...

[InayathUlla Sharieff]

Yes you are correct.

OSPF adjacency would not be formed.

It is stuck in Extract state. 

HTH

Regards

Inayath

***plz dont forget to rate all usefull posts.

[Mahesh Gohil]

so let me go in bit more detail.

Do you have capture which shows it struct in which state. In my case no output entirely.

Regards # Mahesh

[InayathUlla Sharieff]

Here are my outputs:

Config:
R1 
!
interface FastEthernet0/0
 ip address 10.10.10.1 255.255.255.0
 duplex auto
 speed auto

router ospf 10
 router-id 1.1.1.1
 log-adjacency-changes
 network 10.10.10.1 0.0.0.0 area 0
!

R1#sh ip ospf ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           1   EXSTART/DR      00:00:34    10.10.10.1      FastEthernet0/0
R1#

==============R2===========

R2#sh ip ospf ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   EXSTART/DR      00:00:38    10.10.10.1      FastEthernet0/0
R2#

R2
!
interface FastEthernet0/0
 ip address 10.10.10.1 255.255.255.0
 duplex auto
 speed auto

router ospf 10
 router-id 2.2.2.2
 log-adjacency-changes
 network 10.10.10.1 0.0.0.0 area 0
!

HTH

Regards

Inayath

**********Plz dont forget to rate usefull posts****