OSPF priority

[Keith9]

We have a bunch of sites connected via metro ethernet and Extreme 5520's, 450G2's, and x690's at our core.  When we establish OSPF we basically add the vlan, the cost the authentication and the area.

I've noticed that Exos automatically adds configure ospf vlan VLANNAME priority 0.

Everything seems to work for the most part but I'm starting to wonder if I should start changing the priority.  We have a remote site with multiple wan connections so after hours when testing failover by disabling a WAN port at our HQ, our other branch locations peered with an IPSEC VPN over their cable modems to our DR site, which made its way down that 10 gig ring to HQ.  However the cost for these ipsec vpns are higher than the cost to our far site that has multiple connections.  It should have connected via Comcast to that site a few miles away at 50/50mbps and then from that site via 10gig crown castle to HQ.

But it just didnt.  I'm wondering if it has anything to do with the ospf priority, even though our costs are calculated and set properly.

I'm noticing that the remote site only is in ODR / 2WAY state with Comcast sites, whereas at our HQ core on x690s they are in DR and FULL state.  THe remote site has the 5520s with a Premier licence so I don't think its a limitation of the licence.  The HQ site has the core licence which is what was sold at the time of the x690s.

I hope this makes some sense.  I can try to attach a drawing possibly if you need it.  

Basically, I'm wondering how the OSPF priority can influence this differently than ospf cost.  Each site needs to dual peer with remote DR and HQ over wan links.  The sites can have a third adjacency with a netgate ipsec tunnel to a firewall in our colo which is on our 10 gig ring.

[Gabriel_G · Accepted solution]

VLANs receive an OSPF priority of 0 automatically when the switch does not have a Core/Premier license installed at the time of configuration. If you've later added a Core/Premier license, this config is not updated automatically.

A priority of 0 prevents that switch from becoming a BR/BDR for OSPF Broadcast networks therefore requiring another switch to be the DR/BDR, or the use of point-to-point OSPF networks. This is basically an artificial license limitation.

https://extremeportal.force.com/ExtrArticleDetail?an=000090090

https://extremeportal.force.com/ExtrArticleDetail?an=000091267

The OSPF priority only determines which router becomes BR/BDR and does not have an influence on path selection.

Hope that helps!

[Keith9]

After setting the ospf priority appropriately we are getting the results we expect when testing link failures.  Routes take the path we designed as expected now.  Thanks for your insight!

[Keith9]

On our X690 cores at HQ under show configuration ospf , do not have the priority statement on ANY vlan.  They are running core license and sw 22.5.1.7.

But at our Northern "DR HUB" this line appears on every vlan (Just replace vlan name)
configure ospf vlan WAN-COMCAST296 priority 0

These are 5520 switches running 31.7.1.4 and Premier license.  

[Keith9]

On our hub I just threw in priority 2 on that Comcast broadcast wan and now our other sites see FULL to it instead of 2WAY.  After hours will do a test.
Will disable Comcast at HQ and what I want to see is the branches with Comcast talk to that DR Hub via Comcast, and then at the DR hub take the 10 gig crown castle down to HQ.