Troubleshooting pcap_inject

[David Murray <30179198 () student murdoch edu au>]

Hi,

I am writing a little pcap program that is capable of caching and 
replaying packets. I was originally running the program on a little 
embedded x86 AMD Geode but as I was a little concerned with performance 
I decided I would like to see the difference when running on a desktop. 
So, I moved my GNU c application to a Desktop. Everything appears to 
work other than packet injection.

When injecting packets on the Desktop PC's pcap returns the error 
message "send: Message too Long". By printing the packet size of the 
failed injected packet I know that the packet size is 1552 bytes, which 
is larger than the end-to-end MTU of 1500. However, this is confusing 
for me because when running packet injection on the embedded ALIX 
system, which works, the frames are also 1552 bytes. By capturing the 
real data traffic in wireshark I know that the actual wire frame size 
of these packets is 1514 bytes so I am unsure as to what is being added 
to make these frames 1552 bytes.

Perhaps an important difference between the two systems is that on the 
ALIX embedded system, packet injection is happening over a WiFi NIC 
whereas on the desktop system packet injection is happening on the 
Desktop NIC. Does anyone know what the problem could be here or have 
any advice for things that I could try to better refine the problem?

Additional Info:
The little embedded system is an ALIX board running Voyage Linux
I have tried two desktops: DELL and IBM P4's running Ubuntu Intrepid. I 
have also tested a couple of realtek and Intel NIC's.

Thanks for your time
Dave
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