netdev - Experimental network protocol produces "dropping frag"

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Date:	Fri, 7 Dec 2012 15:41:33 -0800
From:	"Templin, Fred L" <Fred.L.Templin@...ing.com>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Experimental network protocol produces "dropping frag"

Hello,

Under the 3.2.17 kernel, I am working with an experimental
tunneling protocol. I am using ip-proto-253 for the experiment,
and have coded the tunnel code in as a module under net/ipv4
by cloning net/ipv4/ip_gre.c. I have been testing the module
by using modprobe to reload the module without rebooting the
machines.

I was successfully able to send and receive packets via the
tunnel and verified that both directions were working using
tcpdump and wireshark which showed ip-proto-253 packets going
in both directions. Since then, however, I recompiled and
reinistalled the entire kernel and rebooted the machines.

Now, I can still send my ip-proto-253 packets, but on the
receiving side I see dmesg output that says:

  "dropping frag"

for every packet received. The input packets appear to be
accounted for when I type "ifconfig eth0" (i.e., the input
packet count is incrementing) but printk's from my tunnel
driver code are not showing up when I type dmesg and
"ifconfig tun0" on the tunnel interface does not show any
input packets. It is as if the receiver has "forgotten"
how to deal with ip-proto-253.

Any ideas on how I may have shot myself in the foot, and
ways to recover?

Thanks - Fred
fred.l.templin@...ing.com