Number of DR and BDR in one OSPF area

[prasunrao_p]

Can there be more than one DR and BDR in a single OSPF area (multi access network)? If yes .Is it posiible that there may be different DR and BDR for different subnets in one single OSPF area? Please explain..

[lgijssel]

Please check the following link.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml

Personally, I have found this document to be helpful with my CCNP study. I believe that it will answer most of your questions.

Regards,

Leo

[prasunrao_p]

Hi leo,

Thanks for the quick response .We have a hsrp implemented solution where there are multiple sub interfaces and the DR and BDR for some sub interfaces are different routers.All these routers are in single area.I have gone through the document ,but it does not state about this scenario (muliple DR and BDR in a single area in a single broadcast network).Any idea?

[lgijssel]

The case you describe indicates a connectivity problem between various parts of the network. Appearently the routers are not able to "see" eachother which results in several discontinuous areas.

Please verify IP connectivity in the network.

Check for access-lists and routers using "no ip classless".

Regards,

Leo

[Richard Burts]

I believe that the original post reflects a fundamental misunderstanding where it is treating a multi-access segment and an OSPF area as if they were the same thing."... in a single OSPF area (multi access network)" Obviously they are different things. A multi-access segment can have only one DR and no more than one BDR. Depending on how many multi-access segments may be in an OSPF area, the area can have many DRs and many BDRs.

HTH

Rick

[prasunrao_p]

Hi,

Sorry for the confusion.Apparently I was referring to one multi access segment where we have more than one DR and BDR .I suppose that was due to some connectivity isues and some misconfiguration in Ospf priorities .Any way thank you every one for your response.

Prasun.

[baldy]

There is only one DR and only one BDR per multiaccess-network, i.e. those that use the broadcast or nbma network types. All other OSPF routers should be capable of taking over DR or BDR duties unless explicitely configured not to. But only one of each active at any one time. If its more then you have problems!

If you have two multi-access subnets in the ospf process on a router then you have two DR's. The router in question may be DR or BDR for both or it may not, btu each network will have only one of each.