Saturday, August 7, 2010


Here I am going to test about what 2WAY/DROTHER State in OSPF is based on shown topology.
I configure the R1 ospf priority as 255 (DR) and R2 ospf priority as 254 (BDR).
Let's examine the output.

From R1(DR) point of view,
R2 will be FULL/BDR and the rest will be FULL/DROTHER state.

From R2(BDR) point of view,
R1 will be FULL/DR and the rest will be FULL/DROTHER state.

Here we go and see 2WAY/DROTHER State from R3,R4,R5,R6,R7 and R8 point of views. The routers which are not DR/BDR (here is R3,R4,R5,R6,R7 and R8) will see each other in 2WAY/DROTHER State. But they see the R1(DR) as FULL/DR and R2(BDR) as FULL/BDR.

Why 2WAY/DROTHER State ? Here is the Q and A from Cisco OSPF FAQ Website.

Q. When I issue the show ip ospf neighbor command, why do I only see FULL/DR and FULL/BDR, with all other neighbors showing 2WAY/DROTHER?

A. To reduce the amount of flooding on broadcast media, such as Ethernet, FDDI, and Token Ring, the router becomes full with only designated router(DR) and the backup designated router(BDR), and it shows 2-WAY for all other routers.

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