all 10 comments

[–]xDizz3rIT depends 1 point2 points  (3 children)

Does it select the DR in this order? -Highest priority becomes DR, if all same priority then: -Highest Router ID

Till there you are correct.

if no RID then: -Highest IP on loopback interface, if not set then: -Highest IP on physical interface

You can't reach the DR/BDR election if there is no RID.

[–]semeningCCNA[S] 0 points1 point  (2 children)

Ahh yes, what I meant by "no RID" is no RID set by the user using the router id command. I can see now it should be a question of priority vs RID - however I've added/mixed the rid selection process in there as well. Thank you !

[–]a_cute_epic_axisJust 'cause it ain't in my flair doesn't mean I don't have certs 0 points1 point  (1 child)

It's just simply highest priority, then highest RID. If you have two routers with the same RID, shit's broken. Same if you don't have an RID at all.

[–][deleted] 0 points1 point  (0 children)

Adjacency wouldn't even form with same RID therefore no DR/BDR election process. If you get to the point where you've got two devices with the same RID in an election process you've hit the part of the code which generally has a comment like

/* shit, you should never get to this point - abort, abort, abort */

[–]zanfarCCENT 0 points1 point  (0 children)

Keep in mind that DR/BDR election based on Priority and RID is an OSPF concept. The device conveniently selecting a RID from a loopback or physical address if none is supplies is a Cisco feature. OSPF doesn't care where your RID comes from, just that you have one, and it's unique. Cisco noticed that those rules are generally followed for interface addresses--especially loopbacks--and so tried to make your life easier.

[–]the-packet-throwerMeow 🐈🐈Meow 🐱🐱 Meow Meow🍺🐈🐱Meow A+! 0 points1 point  (4 children)

Close, except that OSPF must have a router id

[–]semeningCCNA[S] 0 points1 point  (3 children)

I understand that the router will always have an RID (whether you set it or it uses an interface IP) but if you set the priority higher than other routers, will the routers use that to select the DR over the highest RID?

[–]xDizz3rIT depends 2 points3 points  (2 children)

Correct, it goes like this:
1) Highest OSPF priority
2) Highest RID

[–]semeningCCNA[S] 0 points1 point  (1 child)

Excellent thanks guys :)