Tunnel.py sends packages of incorrect size

I am doing test with tunnel.py and following the readme instructions
located gnuradio/gr-digital/examples/narrowband.
on machine A:
sudo ./tunnel.py --tx-freq=2.51G --rx-freq=2.515G -c 50 -r 0.5M
then
sudo ifconfig gr0 192.168.200.1

on machine B:
sudo ./tunnel.py --tx-freq=2.515G --rx-freq=2.51G -c 50 -r 0.5M
then
sudo ifconfig gr0 192.168.200.2

Then I can see packages tx/rx on both machines:
URx: ok = True len(payload) = 54
Rx: ok = True len(payload) = 90
Rx: ok = True len(payload) = 353
Tx: len(payload) = 90
Tx: len(payload) = 54

After I ping from A to B, I found A only sends packages of fixed size
42:
UTx: len(payload) = 42
UTx: len(payload) = 42
UTx: len(payload) = 42
UTx: len(payload) = 42

But the default package size of ping is 56 from the man page. Where did
the
packages of size 42 come from? Anyone has idea?
I am using two USRP N210s, the daughter boards are both XCVR2450.

42 is the length of the ARP request and make sure the other side sends
out
ARP reply, otherwise, the Ping will always fail due to routing issue.

On Fri, Jun 15, 2012 at 9:31 AM, Weixian Z. [email protected] wrote:

sudo ifconfig gr0 192.168.200.2
UTx: len(payload) = 42
Regards,
Weixian Z.


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