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Open Shortest Path First
You will notice the dotted lines connecting the DROther routers to the
DR and BDR routers. Notice also that there are no dotted lines between any
of the DROther routers. The dotted lines represent the formation of adja-
cencies. DROther routers form only two adjacencies on a broadcast multi-
access network--one with the DR and the other with the BDR. The follow-
ing router output indicates the assignments of routers connected via a broad-
cast multi-access network as well as two Frame Relay (non-broadcast multi-
access, or NBMA) network connections.
Note that the Frame Relay connections displayed below do not have DR/BDR
assignments. DR/BDR roles and election will be covered more fully in the fol-
lowing section, "DR and BDR Election Procedure."
RouterA>sho ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface 1 FULL/DROTHER 00:00:32 FastEthernet0/0 1 FULL/DR 00:00:34 FastEthernet0/0 1 2WAY/DROTHER 00:00:32 FastEthernet1/0 1 2WAY/DROTHER 00:00:37 FastEthernet1/0 1 FULL/BDR 00:00:34 FastEthernet1/0 1 FULL/DR 00:00:34 FastEthernet1/0 1 2WAY/DROTHER 00:00:36 FastEthernet1/0 1 FULL/ - 00:00:34 Serial3/0.1 1 FULL/ - 00:00:34 Serial3/1 1 FULL/ - 00:00:35 Serial3/3.1
We need to bring up a few important points about this output. Notice that
four different interfaces are configured to use OSPF.
Interface Fast Ethernet 0/0 shows only a DROther and a DR. You know
that there must always be a DR and a BDR for each multi-access segment.
Deductively, you can ascertain that RouterA must be the BDR for this segment.
Copyright ©2001 SYBEX , Inc., Alameda, CA