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OSPF DR

mikegrous
Level 3
Level 3

Would this be a problem...

All routers area 0

All network types broadcast

There is FR so there are Serial links set at betworktype Non-broadcast

There is a DR for the Broadcast network type

and there is a DR for the Non-broadcast type. Thus there are 2 DRs in area 0. Is this a problem. I can get around it via making the network types Point-to-Multipoint thus no second DR is elected. But do i even have to do that?

3 Replies 3

Richard Burts
Hall of Fame
Hall of Fame

Michael

You seem to assume that having multiple DR in an area is a problem. That is not the case.

DR is elected per segment (per subnet) and is not per area. So it is normal to have multiple DR in area 0 and it is not a problem at all.

HTH

Rick

HTH

Rick

DR is elected per segment (per subnet) and is not per area.

That one statement Cleared up everything. Thank You.

Giuseppe Larosa
Hall of Fame
Hall of Fame

Hello Mike,

the DR concept is link specific: on different links L3 subnets you have different DRs.

No problem in having multiple DRs in the same area.

The DR is the OSPF router responsible to represent the multi-access segment.

What really counts is that all devices connected to the same ip subnet / multiaccess segment must agree on the ip ospf network type to avoid problems.

So you have a DR on each LAN segment and a DR on each FR link that uses main interface or a point-to-mulipoint subifs.

Serial interfaces with HDLC or PPP encapsulation and FR point-to-point subif are seen as point-to-point OSPF networks and no DR is elected

So you don't need to worry about this is normal OSPF behaviour.

Hope to help

Giuseppe

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