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Feature #6298

open

osmo-ggsn not providing MTU of the GTP tunnel to the MS

Added by pespin 3 months ago. Updated 14 days ago.

Status:
New
Priority:
Normal
Assignee:
-
Category:
-
Target version:
-
Start date:
12/08/2023
Due date:
% Done:

0%

Spec Reference:

Description

MTU is provided by PCO in IPv4 and through SLAAC in IPv6 (see https://github.com/open5gs/open5gs/issues/2754 for more info).
I think osmo-ggsn is not yet providing it to the MS, hence why one may not see it while looking at pcaps.
One can check at open5gs on how to submit it.

We probably also want to have it configurable in the vty and apply it on the created tunnel device too.
Probably something to be added through libosmocore ./include/osmocom/core/tun.h ./src/core/tun.c


Related issues

Related to OsmocomBB - Feature #6115: modem: MTU not set properly on tun ifaceFeedbackpespin07/26/2023

Actions
Actions #1

Updated by pespin 3 months ago

  • Related to Feature #6115: modem: MTU not set properly on tun iface added
Actions #2

Updated by laforge 14 days ago

I guess this is just an optimization, right? When the GTP packet exceeds the [outer path] MTU, IP fragmentation will be used. For the very slow speeds of our 2G and 3G networks, the fragmentation/reassembly overhead probably doesn't matter all that much?

Actions #3

Updated by pespin 14 days ago

ACK, I don't recall exactly right now under which circumstances this can be a problem, probably some host in the path not allowing ip fragmentation or so.

I'd say it's no high prio for sure. Still, I thought it made sense to have this ticket created since it's something really missing, and I was looking at related specs/topics at the time.

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