jose,
this list is intended to discuss things specifically around wireshark, so you might be better off finding a network help mailing list for this sort of question
that said:-
The IP identification field is basically used to distinguish IP packets when the following other 3 parameters are all the same - source IP, dest IP and protocol. Thus as packets from A to B and A to C will have different dest IP address, you could in fact have the same identification field and still be able to distinguish packets.
Regards, Martin
MartinVisser99@xxxxxxxxx