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TOPIC: OSPF question - your help needed please

OSPF question - your help needed please 7 years 11 months ago #27820

  • Damien610
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I have 3 routers - London, Ottawa and Brasilla connected via a switch configured on OSPF with Loopback addresses

The show ip ospf neighbour command on each router displays the below….

London (loopback 192.168.31.11)

Neighbor ID Pri State Dead Time Address Interface
192.168.31.22 1 FULL/BDR 00:00:32 192.168.1.2 Ethernet0
192.168.31.33 1 FULL/DR 00:00:35 192.168.1.3 Ethernet0

Ottawa (loopback 192.168.31.22)

Neighbor ID Pri State Dead Time Address Interface
192.168.31.11 1 FULL/DROTHER 00:00:31 192.168.1.1 Ethernet0
192.168.31.33 1 FULL/DR 00:00:33 192.168.1.3 Ethernet0

Brasilla (loopback 192.168.31.33)

Neighbor ID Pri State Dead Time Address Interface
192.168.31.11 1 FULL/DROTHER 00:00:33 192.168.1.1 Ethernet0
192.168.31.22 1 FULL/BDR 00:00:33 192.168.1.2 Ethernet0

My question is why is the DROTHER router displaying FULL as the state :?:
I though only DR and BDR were meant to be full state, shoudnt the DROTHER state be 2-way :?:

The below is taken from a OSPF guide ….

‘On a multi-access network, OSPF routers will only form Full adjacencies
with DRs and BDRs. Non-DRs and non-BDRs will still form adjacencies,
but will remain in a 2-Way State. This is normal OSPF behavior.’
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Re: OSPF question - your help needed please 7 years 11 months ago #27828

  • novembre
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The FULL/DROTHER you see in your examples is the full adjacency from the DR / BDR perspective. You will have a 2-WAY state between routers which are neither DR or BDR.

Maybe an example will help, lets introduce another router into your lab (or slightly modify mine)

Auckland (loopback 192.168.31.44) Elections are rigged such that .33 = DR and .22 BDR

The view from London (192.168.31.11):

Neighbor ID Pri State Dead Time Address Interface
192.168.31.22 100 FULL/BDR 00:00:39 192.168.1.200 FastEthernet0/0
192.168.31.33 200 FULL/DR 00:00:38 192.168.1.100 FastEthernet0/0
192.168.31.44 0 2WAY/DROTHER 00:00:38 192.168.1.102 FastEthernet0/0

The view from Auckland (192.168.31.44):

Neighbor ID Pri State Dead Time Address Interface
192.168.31.11 0 2WAY/DROTHER 00:00:30 192.168.1.101 FastEthernet0/0
192.168.31.22 100 FULL/BDR 00:00:34 192.168.1.200 FastEthernet0/0
192.168.31.33 200 FULL/DR 00:00:39 192.168.1.100 FastEthernet0/0
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Re: OSPF question - your help needed please 7 years 11 months ago #27833

  • SteveP
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@Damien610 - do you have the link to the OSPF guide that you referenced? I really liked (and, for once, completely understood!) OSPF and found it fascinating (not at all like EIGRP!).
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Re: OSPF question - your help needed please 7 years 11 months ago #27834

  • Damien610
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I see :idea: ........thanks novembre for the well worded explaination,

Regards

Damien
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Re: OSPF question - your help needed please 7 years 11 months ago #27835

  • Damien610
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@Damien610 - do you have the link to the OSPF guide that you referenced? I really liked (and, for once, completely understood!) OSPF and found it fascinating (not at all like EIGRP!).

Sure, go to www.routeralley.com/ra/guides.html and select Open Shortest Path First (OSPF) guide
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Re: OSPF question - your help needed please 7 years 11 months ago #27836

  • SteveP
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Hey, that's a pretty cool site. I'll be printing several of the guides off next time that I'm at college - even those which deal with topics that we've covered previously! From my quick skim of the material, it seems that he's got an easily understood method of teaching some complex material.

I can't recall if there's a sticky here for useful sites. If so, routeralley should be in there.
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