What's the point of the "global" OSPF priority command?

[cwkronk1982]

So after doing an OSPF lab, I've found what looks like a global priority setting that appears to do nothing. I know that priority for OSPF is supposed to be set on the individual interfaces. I found that under:

router ospf <process id>

That there is a priority command. I set it to 0 with priority not set on the interfaces and the router still participated in the DR/BDR election. What is this command for?

[luis_cordova]

Hi @cwkronk1982 ,

Could you specify what command you find inside the OSPF configuration?

Regards

[paul driver]

Hello

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@cwkronk1982 wrote:

So after doing an OSPF lab, I've found what looks like a global priority setting that appears to do nothing. I know that priority for OSPF is supposed to be set on the individual interfaces. I found that under:

router ospf <process id>

That there is a priority command. I set it to 0 with priority not set on the interfaces and the router still participated in the DR/BDR election. What is this command for?

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Its a routing stanza command for non broadcast ospf peers for DR election, not so sure why it isn't working at this time but have you set your ospf interfaces to be a non-broadcast network type or it could even  be down to the simulation software I am assuming you are using?

[cwkronk1982]

I believe we have found the answer. It's not the priority command you place on interfaces that determines priority for DR/BDR election, but just the command priority that can be entered after typing router ospf <process id>. It looks like it is used to set the priority for multi-process OSPF instances in which process gets to do the DR/BDR election first when there are multiple OSPF processes running on one router.

[paul driver]

Hello

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@cwkronk1982 wrote:

I believe we have found the answer. It's not the priority command you place on interfaces that determines priority for DR/BDR election, but just the command priority that can be entered after typing router ospf <process id>. 

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I don't think this is correct statement as you can  use the ospf priority command at the interface level which would be also applicable for ospf broadcast network types regards DR/BDR election preference, however for non broadcast you would still require at least one router process neighbour command to bring up those adjacency's.

[cwkronk1982]

I was wrong. It’s actually for priority of the SPF calculation between different processes from what I understand. 

priority (OSPF)

To set the priority that an Open Shortest Path First (OSPF) process assigns to a topology instance for shortest path first (SPF) calculations, use the priority command in router address family topology configuration mode. To return the priority to the default value, use the no form of this command.

priority number

no priority

Syntax Description

number

Priority number for a topology instance. The range is 0 to 127. The default is 64.

Command Default

The default priority number is 64.

Command Modes

Router address family topology configuration (config-router-af-topology)

Command History

ReleaseModification

12.2(33)SRB

This command was introduced.

Usage Guidelines

The priority command is used to set the OSPF processing order for topology instances when an SPF calculation is scheduled and ready to run for multiple topologies. The topology with the highest priority number is processed first. The default priority value is 64.

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This means that when SPF runs it will start with topology that has highest priority first. If you consider voice to be most important then assign it priority 127. Then SPF will run first for voice before maybe data and other applications if you have multiple topologies.

[paul driver]

Hello

Well then we are on about a different command, the opsf priority i was discussing exist in two areas, wasn't aware your meant the ospf priority that is directly applied to the opsf process - apologies for the confusion

Interface
ip ospf x priority x

router porcess
nieghbour xxxx priority