EIGRP Authentication

I have a question that I cannot answer seem to understand the
reasoning behind for so I'm here for some general help.

I was doing a sample lab and I had to configure EIGRP authentication
between routers running frame-relay. I did what I thought was correct
and everything worked.

Well lets say that the two routers became neighbor and routes were
exchanged but here is the part I do not understand.

One of the routers had its IP address on a main serial interface and
the other had its IP address on a sub-interface point-to-point, an
over sight on my part I configured EIGRP authentication on the main
interface and not the sub interface. I did not realize that I had
made this mistake until I was checking the solution. I'm thinking
that maybe it should have not worked but it does.

This got me thinking, what is the difference between what is
configured on the main interface to a sub-interface? Do commands on
the main interface over ride all sub-interface command where these
configuration statements are missing?

Has anyone run across this before? Any feedback would be welcome.

Andy

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Received on Fri Apr 15 2011 - 21:32:45 ART