OSPF question

Answered Question
Mar 15th, 2010
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Hi, all


I have a Catalyst3750 with IPSERVICESK9-M-12.2(50)SE3 .


I change OSPF network type from broadcast to nbma on a SVI, and I put the "priority 0" under SVI as the following.


ip ospf network non-broadcast

ip ospf hello-interval 10

ip ospf priority 0


and also put "neighbor <neighbour ip add>" under OSPF process configuration.


But when I do "show running-config", the "neighbor <neighbour ip add>" command is disappeared from the router's configuration.


By the way, the OSPF adjency with this neighbor can be successfully established.


And when I put the "priority nonzero" under SVI,  "neighbor <neighbour ip add>" command is appearing.


Is this the feature of OSPF??


If so,are there any reference to it in any of the docs?


Best Regards,


Tomoyuki

Correct Answer by Aaron Harrison about 7 years 3 months ago

Hi


For what it's worth, I've seen this behaviour in my lab.


I can only assume that since the neighbor statement is only really required at one end (though I have seen Cisco docs suggested best practice would be to configure it at both ends), and as only the DR/BDR needs to have a connection to all other routers, they have decided to enforce the removal of the 'unnecessary' neighbor statements when you stop the router participating in elections with the priority command...


This doc: (http://www.cisco.com/en/US/docs/ios/12_0/np1/configuration/guide/1cospf.html#wp4801) states re: the neighbor statement on NB networks:


These parameters need only be configured in those devices that are themselves eligible to become the designated router or backup designated router (in other words, routers with a nonzero router priority value


Regards


Aaron


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paolo bevilacqua Mon, 03/15/2010 - 04:15
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You should not change these OSPF settings on a LAN.


If you are worried about peers identity, use authentication.

Correct Answer
Aaron Harrison Mon, 03/15/2010 - 04:39
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Hi


For what it's worth, I've seen this behaviour in my lab.


I can only assume that since the neighbor statement is only really required at one end (though I have seen Cisco docs suggested best practice would be to configure it at both ends), and as only the DR/BDR needs to have a connection to all other routers, they have decided to enforce the removal of the 'unnecessary' neighbor statements when you stop the router participating in elections with the priority command...


This doc: (http://www.cisco.com/en/US/docs/ios/12_0/np1/configuration/guide/1cospf.html#wp4801) states re: the neighbor statement on NB networks:


These parameters need only be configured in those devices that are themselves eligible to become the designated router or backup designated router (in other words, routers with a nonzero router priority value


Regards


Aaron


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t-yamashita Mon, 03/15/2010 - 07:33
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Very good Aaron.


Thank you for your help.


Regards,


Tomoyuki

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