Hi Jakub,
On Wed, Oct 18, 2023 at 10:37:03AM -0700, Jakub Kicinski wrote:
Harald went further and questioned use of the same IP addresses for -U and -C traffic, but even within one endpoint aren't these running on a different port?
yes.
Can someone reasonably use the same UDP port for both types of traffic?
I don't think so. In the entire 3GPP protocol world, the UDP port numbers for GTP-U and GTP-C are fixed. The various signaling protocols allow you to communicate the IPv4/v6 address and TEID of tunnel endpoints, but never allow you to communicate the port number - which hence must always be the well-known port (2123 for GTP-C + 2152 for GTP-U).
Of course somebody could do whatever they want in some kind of internal interface not required to interoperate with any other equipment/implementation/operator, but I'd consider it not falling in your question of "reasonable use".
Regards, Harald