Controling OSPF Neighbors

Answered Question
Aug 26th, 2008
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Let's say I have 4 routers on the same network segment all running OSPF


but I do not want them all to become neighbors, just 2 and 2 is there a way to do this in OSPF ?


without using access lists on interface to block ospf or such methods


Correct Answer by Giuseppe Larosa about 8 years 9 months ago

Hello Arni,

you can take advantage of OSPF authentication:


C and D will have both keys key1 and key2


A will have only key key1

B will have only key key2


so A and B shouldn't become neighbors for the key mismatch


Hope to help

Giuseppe

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satish_zanjurne Tue, 08/26/2008 - 01:58
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use "passive-interface" command !!!


or don't enable ospf on interfaces connecting other 2 routers.

arni.v.skarphed... Tue, 08/26/2008 - 02:02
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dont think that will work


lets say I have routers A, B, C and D


A should neighor with C and D

B should neighbor with C and D


But A and B should not neighbor

and they are all on the same network


if I use passive interface on A or B they wont neighbor with C or D


:)

satish_zanjurne Tue, 08/26/2008 - 02:20
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It depends, on which interfaces you are defining as passive-interface.


In this case define interface on Router B which is connecting to Router A as passive-interface.


HTH..



arni.v.skarphed... Tue, 08/26/2008 - 02:23
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Ok as I said before they are all on the same network, so each device only has one interface to connect to the other 3



satish_zanjurne Tue, 08/26/2008 - 02:34
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Are these routers are connected on LAN , having same subnet??



Correct Answer
Giuseppe Larosa Tue, 08/26/2008 - 02:55
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Hello Arni,

you can take advantage of OSPF authentication:


C and D will have both keys key1 and key2


A will have only key key1

B will have only key key2


so A and B shouldn't become neighbors for the key mismatch


Hope to help

Giuseppe

glen.grant Tue, 08/26/2008 - 03:23
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Passive interface would work on a interface . If you are saying that there is one interface to another router then if you don't want the particular router to be a ospf participant then then passive interface the router interface or don't setup ospf at all on the router is which case you will need default static routes pointing to the next hop and somewhere on a ospf router you will need statics pointing back to the boxes that are not running ospf for the subnets on that router. . Not sure why you want to do this.

francisco_1 Tue, 08/26/2008 - 05:45
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If the routers are on the same subnet on the same broadcast network, the way i will do it is enable the network type "point-multipoint nonbroadcast" under the interface on the two routers and manually peer those routers with the neighbour [ip address] under the OSPF process. The routers will use unicast instead. No need for ACL or route-map or authentication.


Just beware that you will not have the DR/BDR functionality.



Francisco.

Carl Ratcliffe Tue, 03/17/2015 - 06:34
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Thanks, this topic is 7 years old but this was the only/best solution I could find that would work so that I could have multiple OSPF devices on the same shared subnet then select which of these devices became neighbours.

Thanks

Carl Ratcliffe

Preston - Lancashire - England

 

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