Mac spoofing using libnet

[preceptor () hushmail com]

I'm currently looking at a system which seems to avoid using ARP to resolve a mac address. Instead, it's looking at the 
mac address embedded in the packet.
I was wondering, if there are any tools built around Libnet (or similar) which are able to handle a whole tcp/IP 
session. (nemesis is the sort of idea, but unfortunately the test I'm looking at is an HTTP request, which is a little 
challenging using nemesis).
Alternatively, I was looking at having two NICs with different mac addresses, duplicate IP addresses, and network 
cables such that one of the interfaces is send only.
Can anyone point me at such a tool? (or an example of libnet used to do a whole session). I'm content enough to put 
this together, but I don't really want to re-invent the wheel if it's already been done.

Cheers
Ed Rolison

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