-
1. Re: ospf DR
Martin Jul 22, 2011 8:51 PM (in response to Scott_O'Brien)DR and BDR must have connections to all other routers, right ?
so, if someone accidentally turn on router with very high loopback IP, re-election happens right away, you will have a BIG mess on your hands
-
2. Re: ospf DR
Scott_O'Brien Jul 22, 2011 8:55 PM (in response to Martin)but as there is no pre-empt then even if that router gets turned on unless the current DR gets reloaded or the neighbor relashioships get reset then it would have no effect, and even then if there was a router that was up after befoure the high loop back router on after the DR router then that router would take affect regardless of the priority.
-
3. Re: ospf DR
Brian McGahan - 4 x CCIE, CCDE Jul 22, 2011 9:18 PM (in response to Scott_O'Brien)In reality as long as all the routers on the segment have full layer 2 reachability to each other it doesn't matter who the DR or BDR is. This design only makes a difference if you have emulated broadcast networks over point-to-point layer 2 technologies such as Frame-Relay or ATM partial-mesh, DMVPN, or VPLS.
In general there is no preemption of the DR in OSPF, but there are corner case designs that can occur which results in preemption, and could potentially result in a loss of connectivity.
The normal behavior should be that the election occurs for the DR and BDR, then if the DR goes down the BDR takes its place, and a re-election occurs for the BDR.
Here is an example case of where this design can break down and cause failures in the topology: http://ieoc.com/forums/p/16073/133783.aspx#133783
-
4. Re: ospf DR
Scott_O'Brien Jul 22, 2011 9:23 PM (in response to Brian McGahan - 4 x CCIE, CCDE)thanks but how do you make it so that only the DR and BDR are part of an election? the only way i can think of is if you set all routers to a priority of 0 except the DR and BDR then if the DR goes down the BDR takes over and when the DR comes back online set the BDR'S priority back to 0 then once the DR is elected again re-set the BDR'S priority back.
-
5. Re: ospf DR
Martin Jul 22, 2011 9:38 PM (in response to Scott_O'Brien)default priority is 1
also, do u know about clearing ospf instead of re-booting routers ?
-
6. Re: ospf DR
Scott_O'Brien Jul 22, 2011 9:39 PM (in response to Martin)yea clear ip ospf processes, i just think its an odd way and cisco could have done it better
-
7. Re: ospf DR
Martin Jul 22, 2011 10:09 PM (in response to Scott_O'Brien)have you read this tread ? if not read it
-
8. Re: ospf DR
Brian McGahan - 4 x CCIE, CCDE Jul 22, 2011 10:34 PM (in response to Scott_O'Brien)Scott_O'Brien wrote:
thanks but how do you make it so that only the DR and BDR are part of an election? the only way i can think of is if you set all routers to a priority of 0 except the DR and BDR then if the DR goes down the BDR takes over and when the DR comes back online set the BDR'S priority back to 0 then once the DR is elected again re-set the BDR'S priority back.
If the priority is zero, the router will not participate in the DR/BDR election. You can technically do what you proposed to influence the election, but you wouldn't want to. Every time DR is re-elected is causes a reconvergence event, during which packets are dropped until the network can reconverge. Like I said, in a real design it doesn't matter who the DR or BDR are unless you have some complex non-broadcast or emulated broadcast topology.