Snort mailing list archives

Re: The detect function


From: Russ Combs <rcombs () sourcefire com>
Date: Wed, 2 Jan 2013 13:33:20 -0500

Suggest looking at your packet(s) in something like wireshark to see what
the encapsulations are.  In wireshark, open the "Frame" to view "Protocols
in frame".  You may see something like "eth:vlan:ip:tcp:http" or
"eth:ip:gre:ppp:ip:tcp:http".  That latter has GRE (you can google that)
and requires that Snort be built with GRE support (enabled by default).
Please send a pcap if that doesn't get you moving.

On Tue, Dec 18, 2012 at 4:57 AM, Shimrit Tzur <shimritd () gmail com> wrote:

I can see now that I'm getting into the ifdef GRE in the function and this
is the reason that it returns.
Can someone explain me why? what is this gre? the input contains http or
tcp packets.
Thanks!


On Tue, Dec 18, 2012 at 9:39 AM, Shimrit Tzur <shimritd () gmail com> wrote:

Hello all,
I know Snort for a while but new in developing it.
I'm trying to trace the function flow of a standard http packet.
I notice that in the detect function of (detect.c) there is a switch-case
statement on "p->outer_family" where the options are AF_INET and AF_INET6.
In my case the value is 0 so the program goes to the default option which
simply returns so the fpEvalPacket isn't called.

My question is what is the meaning of this outer_family field of the
packet and why it is 0?

Thanks a lot,
Shimrit




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