The OSPF interface priority is the parameter that controls DR election. Its default value is 1. When OSPF interface priority is 0, the router is not eligible to become a DR. If a router comes up on a network segment and there are no other routers there already, it will become a DR. If there is an existing DR (or BDR), the new router will NOT attempt to preempt them. If several routers come up at roughly the same time (or the DR fails), a new DR election process will be triggered. The router with the highest priority value then will become a DR.
In short, the DR/BDR election process is not deterministic and depends on the sequence of events. Therefore it is important to be able to prevent routers from EVER becoming DR/BDR, when that is appropriate for the topology in which they are connected. This si accomplished by setting their OSPF interface priority to 0: ospf set interface priority 0 So there has to be a DR first and after that there will be an BDR If you start an router on itsself not yet connected to the network it will start as an BDR. Quoting "DeVoe, Charles (PKI)" : > I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In > the OSPF section under the discussion of DR and BDR (page 171) he says that > the BDR is chosen first and that the DR is chosen from the reaming list. > That seems illogical and backwards. Can someone please confirm or deny and > explain it. Thanks > **Please support GroupStudy by purchasing from the GroupStudy Store: > http://shop.groupstudy.com > FAQ, list archives, and subscription info: > http://www.groupstudy.com/list/cisco.html > > Iwan Hoogendoorn Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=73510&t=73504 -------------------------------------------------- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
