GTP-U support

[Zplusless]

Hi team,

I am currently evaluating this project for a 5G network scenario. I noticed that GTP-U (GPRS Tunneling Protocol User Plane) support seems to be missing. Could you please clarify if there is a roadmap to support GTP-U?

[n1tr0-5urf3r]

Hi Zplussless,

GTP-U is currently not in the roadmap, but only because nobody has requested it yet! :)
Depending on what features of GTP-U you need, it could be easy to add.

The header stack would basically look like:
Ethernet | IPv4/v6 | UDP, dport=2152 | GTP-U | Inner IP | UDP | ..., right?

The problem with GTP-U is that it has no indicator in the protocol about the inner protocol (like if IPv4 / IPv6 follows after the GTP-U header).
So we would have to go either with static inner IPv4 or IPv6 only since parsing in P4 is otherwise not possible.

For the TEID, do you also need some stateful mechanisms to get the mapping, or is generating a customizable value for the TEID sufficient? The latter would be easy to do. Is a message type of 0xff (user data) sufficient?

Are there any extensions of GTP-U (sequence numbers, ...) that you need? That could complicate things.

[n1tr0-5urf3r]

Follow-Up: Was easier to do than expected. Here is a screenshot of the Configuration GUI for GTP-U:

And here is a wireshark capture of generated traffic:

Does that work for you? I will make it available soon on the nightly branch.
Edit: 9c28446

[Zplusless]

Great! Is it possible to use one P4 port to generate GTP-U traffic and another port to receive the decapsulated traffic (also collecting traffic statistics)? Conversely, does this setup also work for the encapsulation process?

[n1tr0-5urf3r]

Yes! You just have to ensure that the inner UDP payload remains untouched, since this contains the sequence numbers and timestamps for collecting the statistics.
You can generate Ethernet | Outer IPv4 | Outer UDP | GTP-U | Inner IPv4 | Inner UDP | ..., have some networking equipment that decapsulates, and return traffic like Ethernet | Inner IPv4 | Inner UDP | ... to P4TG to the same or a different port.