OSPF Full/Drother and Full / -

when running the command : show ip ospf neighbors, I can see in some configurations
Full/Drother
and in other configurations
Full/-

I would like to know the difference between  OSPF  Full/Drother and  Full / -

Thank you
jskfanAsked:
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JustInCaseCommented:
FULL/DR    FULL/BDR   2WAY/DROTHER  
DROTHER - Designater Router Other
Are present between in OSPF broadcast and nonbroadcast networks (networks that are electing DR and BDR). In broadcast and nonbroadcast networks adjacency is established only with DR and BDR on link.

FULL/- is present in point-to-point and point-to-multipoint networks. With this type of links all OSPF routers create adjacency to each other and there is no DR BDR election.
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jskfanAuthor Commented:
I tested :point-to-multipoint networks.
 the Show ip ospf neighbor on the:

Hub#sh ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
3.3.3.3           0   FULL/  -        00:01:33    172.16.123.3    Tunnel0
2.2.2.2           0   FULL/  -        00:01:49    172.16.123.2    Tunnel0
Hub#

Open in new window


on the spokes :
Spoke1#sh ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           0   FULL/  -        00:01:59    172.16.123.1    Tunnel0
Spoke1#
Spoke1#sh ip ospf neighbor
Spoke2#sh ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           0   FULL/  -        00:01:36    172.16.123.1    Tunnel0
Spoke2#
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JustInCaseCommented:
I forgot to write that FULL/DROTHER cant be sen only when "show ip ospf neighbor" is issued on DR and BDR (so in broadcast and NBMA networks) between DR (or BDR) and OSPF routers that are DROTHERs on that network segment.

In your case, since you are on point-to-multipoint network there is no DR/BDR election, so that's why there is - after /.
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jskfanAuthor Commented:
I have not tried it yet, but I think FULL/DROTHER, will show up in Broadcast and non-broadcast network types, when the Spokes are configured with IP OSPF Priority 0
so the Hub will be always be the DR and the spokes will never be elected neither DR nor BDR.
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JustInCaseCommented:
Yes, but not only when neighbors are configured with priority 0, but in broadcast or NBMA network with 3 or more  OSPF routers when "show ip ospf neigh" is issued on DR or BDR. Can't be see on any DROTHER router since on those devices you can only see one of the following FULL/DR, FULL/BDR or 2WAY/DROTHER. 4 or more OSPF routers in the bradcast or NBMA network segment are needed to be able to see state 2WAY/DROTHER (between 2 DROTHER routers).
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jskfanAuthor Commented:
Thank you for the valuable info
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JustInCaseCommented:
You're welcome.
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