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ashleyreed4218
Beginner

OSPF - duplicate router ID

%OSPF-4-DUP_RTRID_AREA: Detected router with duplicate router ID 192.168.33.3 in area 1

I am troubleshooting a network. My access to the onsite VPN machine keeps going in and out and I have noticed that the logs show the output above. I am assuming that these logs indicate an OSPF related config issue. Also, when I try to ssh to one of the devices on my network, it logs me out after a while. To me, this suggests something like a route path flapping from one switch/router to the other.

One of my associates said perhaps making certain interfaces on my switch passive-ospf?

Does anyone have any suggestions?

Thank you in advance,

Ashley

2 ACCEPTED SOLUTIONS

Accepted Solutions
Kyle McKay
Beginner

This error message is exactly what it says. You have two or more routers in the OSPF domain sharing the same Router ID - which is a major no-no.

There is no legitimate reason (that I can think of) for you to have two OSPF routers with the same Router ID, so this would be a configuration issue, for sure.

You will need to audit your routers and determine why there is a duplicate - then you will need to resolve it by changing the duplicates to take on a new Router ID.

View solution in original post

John Blakley
Advisor

The router id is chosen, by default, router-id configured under the process (preferred), loopback address on the router (ospf will pick a loopback if one exists over a physical interface with an IP address), or the last option is the highest ip address on the box. If a router has been decommissioned and had the address of 192.168.33.3 and was changed to something else, ospf will not reselect a router id until the process is either restarted or the router has been rebooted. The best thing to do is on this router, change the router id under the ospf process to make it more predictable:

router ospf

router-id

You'll have to restart the ospf process:

Router# clear ip ospf process

Answer yes

Here's a document that could explain much better than I can:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080117102.shtml

HTH,

John

HTH, John *** Please rate all useful posts ***

View solution in original post

6 REPLIES 6
Kyle McKay
Beginner

This error message is exactly what it says. You have two or more routers in the OSPF domain sharing the same Router ID - which is a major no-no.

There is no legitimate reason (that I can think of) for you to have two OSPF routers with the same Router ID, so this would be a configuration issue, for sure.

You will need to audit your routers and determine why there is a duplicate - then you will need to resolve it by changing the duplicates to take on a new Router ID.

John Blakley
Advisor

The router id is chosen, by default, router-id configured under the process (preferred), loopback address on the router (ospf will pick a loopback if one exists over a physical interface with an IP address), or the last option is the highest ip address on the box. If a router has been decommissioned and had the address of 192.168.33.3 and was changed to something else, ospf will not reselect a router id until the process is either restarted or the router has been rebooted. The best thing to do is on this router, change the router id under the ospf process to make it more predictable:

router ospf

router-id

You'll have to restart the ospf process:

Router# clear ip ospf process

Answer yes

Here's a document that could explain much better than I can:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080117102.shtml

HTH,

John

HTH, John *** Please rate all useful posts ***

Thanks John and Kyle.

But if I clear the ospf process is it going to cancel all ospf in my area? As in I will have to reconfigure OSPF from scratch? Or can I simply change the router-id on my duplicated routers? Also, is a router id different than an IP address?

Ashley

Ashley,

The router ID is used in OSPF for things other than adjacencies. They're used for other things like virtual links, identifying other routers in the ospf database, etc., so yes you can set the router ID as an address that doesn't even exist on your router and adjacencies will still come up. As far as clearing the ospf process, it doesn't clear the configuration so you won't need to reconfigure anything. What it does do is tear down adjacencies, so if you do this during business hours you can expect a slight outage until the neighbors come back up. You can change it on the other routers as well instead of this one. I'd recommend setting it to something that would make it easily identifiable.

HTH,

John

HTH, John *** Please rate all useful posts ***

John's explanation is right-on.

The router-id is an identifier attached to each and every router in the OSPF domain. This router-ID MUST be unique because every entry in the link-state database references the Router-ID in which it came from. If you have two or more routers with the same ID, this process does not work properly.

The Router-ID is selected based on the following:

First of all, if you manually define a router-ID in the OSPF process, that will become the router-id.

Secondly, if there is no router-ID defined, the highest Loopback IP address is automatically selected.

Lastly, if there is no loopback address, the highest interface IP address is automatically selected.

The one caveat is that in order to change the router-ID you must actually clear the ospf process like John mentioned. This is because the process essentially needs to re-initiate its adjacencies with the NEW Router-ID. When you clear the OSPF process, you will incur an outage while the router re-establishes its OSPF adjacencies with the new ID.

Joseph W. Doherty
Hall of Fame Expert

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Posting

Just want to expand on potential impact of clearing the OSPF process.  Effectively, for routing, results would be much like rebooting the router although much, much, much faster recovery.

If you had redundant paths, it's possible to make clearing the OSPF session "hitless".  This is done by effectively costing traffic away from the router you intend to "clear" before you do so.