The 'null' option is because you have 2 ways of configuring OSPF authentication. One is by doing 'link' or 'neighbor' authentication by using the command you specify. The other is by doing Area authentication. The 'null' option on the interface is to override the area authentication. So when area authentication is configured and null is configured under the interface, than that adjacency is NOT authenticated.
Another thing would be if I was asked in a task to make sure that that adjacency is NEVER authenticated, I would always configure 'null' even if area authentication is not configured, just to be sure and to give proctors a proof that I understood the question :-) -- Regards, Rick Mur CCIE2 #21946 (R&S / Service Provider) Sr. Support Engineer – IPexpert, Inc. URL: http://www.IPexpert.com On Tue, Sep 29, 2009 at 10:06 AM, cyrus riobah <[email protected]> wrote: > Hi All, > > R4(config-if)#ip ospf authentication ? > message-digest Use message-digest authentication > null Use no authentication > <cr> > > What does this “null” really mean? If it’s no authentication, then is > there any need of wasting time coming all the way to configure > authentication and you just leave it at “null”? Isn't better to leave > it without any authentication? or what does it really refer to here? > > > Cyrus > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com >
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