OSPF priority vs cost

[Mark1110]

i have two data center. sharing data with each other via isp ckt. Port channel coming from router has configure priority as well as ospf cost. I want to know what's the difference between priority and cost. Also, can we just use cost to make routing decision?

I will make a tunnel between two data center router for backup. and want to use high cost for ospf so it prefer other routes. 

Thanks,

Mark

[Jon Marshall · Accepted solution]

OSPF priority is to do with election of DR/BDR. 

If you want to influence the path taken between the DCs use cost. 

Jon

[Joseph W. Doherty]

As Jon (correctly) describes the difference between using OSPF priority, and OSPF cost, just wanted to note, for the latter (i.e. cost), cost is set, per interface, for egress, however, on Cisco devices, by default, they will "auto compute" an OSPF cost based on what the router "believes" the interface bandwidth is, or what it's set to, via the bandwidth statement.  Also note, Cisco computes its auto cost based on 100 Mbps being the highest bandwidth (on later networks which commonly have links with more bandwidth, you'll want to change the default OSPF highest bandwidth).

[Mark1110]

Thank you Joseph

[Mark1110]

Thank you Jon.