CCIE Pursuit Blog

July 19, 2007

How OSPF Priority 0 Works

Filed under: Cisco,IOS,OSPF — cciepursuit @ 8:00 am

I was looking at some of the options in the OSPF “neighbor” command, when I ran across this:

When the router first starts up, it sends only hello packets to those routers with nonzero priority, that is, routers that are eligible to become designated routers (DRs) and backup designated routers (BDRs). After the DR and BDR are selected, DR and BDR will then start sending hello packets to all neighbors in order to form adjacencies.

I’ve never really thought about what happens when you configure an interface with an OSPF priority of zero – I just knew that it would take that interface out of the DR/BDR election.  It’s interesting to see how simple and elegant the actual process is.


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