Subject: [rbridge] Tree adjacency check and RPF check

From: keshav karedla <[email-masked]>
Date: Wed, 18 Jan 2012 18:14:42 +0530

Hi Authors,

Can you please tell us the scenarios where Tree adjacency check fails and
RPF check passes and vice-versa.
I am not clear whether these two checks are required or not, what I am
thinking is only RPF check will do the both jobs.

please Clarify.

Regards,
Keshav
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From: Donald Eastlake <[email-masked]>
Date: Wed, 18 Jan 2012 09:07:54 -0500

Hi Keshav,

> RPF check passes and vice-versa.

I assume you are talking about the checks in Section 4.5.2 of RFC 6325.

The Tree adjacency check only applies on a multi-access link, such as
an Ethernet link, where they might be a station sending to you that is
not a Tree adjacency. It is basically a test on the source MAC address
and tree root nickname.

The RPF check is a check on the triplet (receiving port, ingress
nickname, tree root nickname) to see it if corresponds to one allowed
by the receiver based on the distribution trees it has built. It does
not involve the source MAC.

> thinking is only RPF check will do the both jobs.

Well, the TRILL base protocol specification currently requires both
tests. You could certainly combine them by testing a quadruplet of
fields that included the source MAC.

If everything is stable and operating properly, you don't need to do
any tests at all. If there are routing transients and ports/links
going up and down and/or some end station trying to forge stuff, I
think you are better off applying both tests.

Thanks,
Donald
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