Subject: [Tsvwg] SCTP UDP encapsulation ports

From: Mark Butler <[email-masked]>
Date: Mon, 10 Apr 2006 13:33:12 -0600

On the topic of SCTP UDP encapsulation ports, I suggest that for 
practical reasons adopting a convention of using the same port numbers 
for both the inner (SCTP) and outer (UDP) ports would be a good thing 
for the following reasons:

1. Allows multiple userspace SCTP/UDP applications (including server 
applications) to operate simulataneously.
2. Allows the local UDP implementation to handle port allocation and 
security
3. Does not require a centralized proxy process or device.
4. Does not require DNS extensions
5. Allows independent port forwarding on common NAT devices.

The downside is that the SCTP/UDP port space necessarily becomes a 
subset of the UDP port space, which would require different well known 
ports to be adopted for SCTP/UDP applications in some cases. 

A typical use case for userspace SCTP/UDP would be a web browser running 
in an environment without kernel space SCTP support (e.g. Windows) and 
located behind a common NAT device accessing a web server that accepts 
TCP, SCTP/UDP, and SCTP/IP connections, on TCP port 80, UDP port 80, and 
SCTP port 80 respectively.  If there were actually a constituency for 
using UDP port 80 for something else (its hardly useful for HTTP), a 
different well known port would have to be adopted for that case. 

Comments?

 - Mark B.