Re: [tcpm] SYN/ACK Payloads, draft 01

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Adam Langley wrote:
| On Wed, Aug 13, 2008 at 3:15 PM, Joe Touch <touch@isi.edu> wrote:
|> This is, IMO, the most compelling argument that this mechanism ought to
|> be bound to a TCP port, not a TCP option.
|
| Although that removes any ability for it to be opportunistic since the
| latency of trying an alternative port is very high. Many sites will
| drop SYNs on ports other than 80 or 443.

Sites that understand this option would be listening on the desired
ports. It's trivial to issue two SYNs and wait to see which ones are
returned.

Further, I'm not even sure how to write the application at the server -
one that responds with different data depending on signals in a SYN.
What does that even mean, and how does the TCP API (as specified in
RFC793, e.g.) need to be extended to support that?

| Even if the original port
| were to advertise the alternative port for future connections, many
| clients are behind firewalls that will restrict their outbound
| connections.

Firewalls and NATs also sometimes munge TCP options, especially ones
they don't understand, FWIW.

Joe

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