Someone fancy explaining what the ISN is? (TCP header, corresponds to SYN flag=1)

[Miscbrah]

Just not sure I get it, but maybe I do.

 

So in the TCP header you have your SYN flag in, well, flags set to 1 for the 3-way handshake. Otherwise, if the flag's set to 0 then the sequence number is just the place of that packet in the sequence.

 

That right so far?

 

If so, or even if not, how is the initial ISN determined? Does the machine/thing requesting the TCP connection just make it up and then wait for the acknowledgement with that ISN +1 back from the machine/thing it's requesting a connection from?

 

Bloody networks. We should all go back to passing notes instead.

 

Thanks in advance to anyone answering.

[OB1]

It's a randomly generated number between 0 and 4,294,967,295. Methods for determining it vary.

There's a bit more info here under Selecting the Initial Sequence Number.

[Miscbrah]

Ooh cheers, and that link's nice and handy!