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Beginner

Duplicate IP addresses on my network?

Hello All:

I think I may have a duplicate IP issue. My connection looks to be intermittently working, sometimes I can't access it, then sometimes I can but I will be disconnected after 1 minute or so.

Does anyone have any suggestions on how to approach this issue?

Thank you in advance,

Ashley

3 ACCEPTED SOLUTIONS

Accepted Solutions
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Check Switch Logs if you have enable logging buffered you will get duplicate ip address logs in switches.

*** Do Rate All Helpful Posts***

Jawad

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This message is because you have an OSPF problem. You may have the same IP address configured on two of your loopback interfaces.

If you post up some scrubed configs we may be able to help you find the offender.

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Take a look at the other router that is terminating your SVIs. I would wager its IP is 33.3 as well, but it should be 33.2.

Also this interface's IP would have been selected as the router ID because it was either hard coded as the router ID under the OSPF process, or because you do not have a loopback interface. You could try giving the devices a loopback address, as this is best practice for OSPF. After you configure the loopbacks you would need to clear the OSPF possess to get the device to pickup the new router ID.

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7 REPLIES 7
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Enthusiast

Could you provide some more details about your network? There are a lot of things that could cause intermittent connectivity. What makes you think it is a duplicate IP?

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Gregory:

It's just a small network with 2 servers, 2 switches and a router. The switches are layer 3. I did a show log on one of my switches and got this:

Apr  4 16:14:14.718: %OSPF-4-DUP_RTRID_AREA: Detected router with duplicate router ID 192.168.33.2 in            area 1

Highlighted

This message is because you have an OSPF problem. You may have the same IP address configured on two of your loopback interfaces.

If you post up some scrubed configs we may be able to help you find the offender.

View solution in original post

Highlighted

You can help find the offender? How? I know what the offender IP address is, but I can't find it.

Here is the latest config:

Apr  4 16:25:15.055: %OSPF-4-DUP_RTRID_AREA: Detected router with duplicate router ID 192.168.33.3 in area 1

Apr  4 16:26:20.159: %OSPF-4-DUP_RTRID_AREA: Detected router with duplicate router ID 192.168.33.3 in area 1

interface Vlan33

description LAN2

ip address 192.168.33.3 255.255.255.0

ip igmp query-interval 20

standby 33 ip 192.168.33.1

standby 33 timers 1 3

standby 33 priority 110

standby 33 preempt

!

Highlighted

Take a look at the other router that is terminating your SVIs. I would wager its IP is 33.3 as well, but it should be 33.2.

Also this interface's IP would have been selected as the router ID because it was either hard coded as the router ID under the OSPF process, or because you do not have a loopback interface. You could try giving the devices a loopback address, as this is best practice for OSPF. After you configure the loopbacks you would need to clear the OSPF possess to get the device to pickup the new router ID.

View solution in original post

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VIP Mentor

Hello,

To obtain the the mac-address  router/l3 switch

sh arp | in x.x.x.x

sh mac-address | in x.x.x.x

Location of device with ip -  L3 switch

sh mac-address address xxxx.xxxx.xxxx

Shutdown the interface and repeat process

if you have a duplicate then it will show up with a different mac-adddress and location

Howerver this could be something else causing this connection loss!

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
Highlighted

Check Switch Logs if you have enable logging buffered you will get duplicate ip address logs in switches.

*** Do Rate All Helpful Posts***

Jawad

View solution in original post

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