source ports

[atassone]

A simple question:

do I break some RFC rule if I generate TCP traffic with source port below 1024 (i.e. source port 80 - destination port 80) ?

I didn't manage to find any place where that's explicitly forbidden.

TIA.

[Kevin Dorrell]

I don't think so. I see some protocols that always use the same source port as destination port, NTP for example (port 123), or NBT on tcp/137. The convention for using different high source ports for protocols such as HTTP, is so that the target can distinguish between the many different sessions that might be going in on port 80.

[mmiklic]

Technically, you are not breaking any rules. A lot of services listen on and generate traffic on source ports under 1024. It just means that these are well-known ports and should be used mostly by servers and not by clients. So if you are a client and have a proprietary protocol sending TCP packets from port 80 for example, than you are not complying to IETF recommendations. Still no-one can take you to court for that ;)