On Fri, Sep 18, 2009 at 10:35:32AM -0500, Manish Aggarwal wrote:
> HI,
> I have a query about the Sequence number in the ESP Header.
> If for any packet, the receiver finds the seq number as ZERO, what is the
> desired behavior..?
> 
> Should this result in the anti-replay check failure..?
> Should this be treated as a corrupted packet..?

Solaris/OpenSolaris treats 0-on-the-wire as an anti-replay failure.  Here's
the code that does early-replay-checking (i.e. replay checking so obvious you
don't need to crunch the authentication algorithm):

http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/inet/ip/sadb.c#6156

And here's ESP calling, and bumping the appropriate bean-counters for
"early-replay drop":

http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/inet/ip/ipsecesp.c#1239

Hmmm, the comment here is quite old.  We *do* check for collisions in
early-replay, and have since AH/ESP support arrived in Solaris.  Must've been
a leftover from bringup...

Hope this helps,
Dan
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