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Beginner

ospf 2way issue

We have direct layer 3 ospf links between 2 cores switches. We also have a trunk running between these switches.  I setup SVI's  and ospf is 2way between SVI's. I tried to shut the layer 3 interface but ospf on SVI did not get out of 2way.

5 REPLIES 5
Beginner

Re: ospf 2way issue

Can you please share the configuration and topology diagram of your setup?

Hall of Fame Expert

Re: ospf 2way issue

Hello Raj-toor,

the neighbor state two way is not always a sign of a problem.

If there are other OSPF routers active on the IP subnet of the SVI Vlan interface, both switches can be DROther ( not elected DR neither BDR), in this case between two DRother devices the neighborship is stopped at state two way.

To check if this is the case it is enough to issue a

show ip ospf neighbors

 

and

show ip ospf interface Vlan X

 

where X is the SVI Vlan X.

 

As a final note, the neighbor state between core switches on SVI Vlan X is not influenced in any ways from the type of OSPF neighborship on the routed link between the core switches as it is treated as a different network segment.

On the routed link between the two core switches if they are the only two OSPF routers the neighbor state is FULL/DR or FULL/BDR if using the default network type of broadcast. IT is FULL/- if you have used ip ospf network point-to-point.

 

So what you see in Vlan X can be normal and not an issue, if other OSPF routers are present in Vlan X and the two core routers are not the DR or BDR but DRother. In this case a FULL/DR and FULL/BDR is reached only with the current DR and the current BDR on the network segment = L2 VLAN broadcast domain.

 

Hope to help

Giuseppe

 

Beginner

Re: ospf 2way issue

Thanks fro the replies. This command somehow got inserted to the config. I don't know how but it did, Removing it resolved the issue as it would not allow any svi to become DR.

 

IP ospf priority 0

Highlighted
Hall of Fame Expert

Re: ospf 2way issue

Hello Raj-toor,

yes in OSPF the interface command ip ospf priority 0 makes the device not eligible for DR or BDR role.

If all devices have this command on an SVI and the OSPF network type of broadcast (default ) is in use the devices will be stucked in two way state waiting for someone to become DR and BDR.

Removing that command solves the problem you can use an ip ospf priority 50 if you want to make a device the DR.

Cisco default values for OSPF priority is 1.

 

Hope to help

Giuseppe

 

Re: ospf 2way issue

OSPF routers on multi-access segments synchronize their  databases with their Designated Router (DR) or a Backup Designated Router (BDR) only. The OSPF status between two routers transitions to Full only if at least one of them is a DR or a BDR.  The state remains Two-way between a pair of routers if both are drothers. 

 

Reference - 

https://community.cisco.com/t5/networking-documents/ospf-neighbors-are-stuck-in-the-two-way-state/ta-p/3130948.

https://learningnetwork.cisco.com/thread/15136

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