Building a packet from scratch (under Windows)

[MarkMLl]

I know that you've seen the DF flag but it's not relevant to local operation particularly if application-level messages already fit inside the lower-level MTU.

Working from memory for example sizes, it would be relevant if you were sending 1 MByte messages over Ethernet with the standard 1K-ish MTU, or 64K messages over ATM with frame size 48 bytes.

Apart from that, and I can assure you that we are all getting sick of trying to hammer this home, TCP is stream-based and neither end of the link should be making assumptions about fragmentation. If the equipment with which you are trying to communicate is assuming that just because it sees the first byte of an application-level message it can recover the final one as part of the same operation then it's broken, what's more that design flaw could potentially result in a security vulnerability.

MarkMLl