Osmo-ggsn MTU issue with Kernel GTP

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Harald Welte laforge at osmocom.org
Tue Apr 13 12:14:48 UTC 2021


Hi Keith,

On Tue, Apr 13, 2021 at 11:10:18AM +0100, Keith A. Milner wrote:
> However, if I change to using Kernel GTP, by changing the gtpu-mode to 
> "kernel-gtp", traffic will not route (and, yes, I have done modprobe gtp). After 
> some exploration, it appears the tun device is being created with an MTU of 
> zero which then, cannot pass traffic:

I think this one is fixed in
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/net?id=e21eb3a065a2d90ee3bb06cc2e77acad403ec7cd
but "of course" Debian 10 is using a too old kernel to contain that fix.

You could ask Debian if they'd back-port it to the stable kernel?

We would certainly also be happy to accept a patch mentioning this in the user
manual, or a patch that makes osmo-ggsn check the MTU at startup time and print
some big error message into the log.

-- 
- Harald Welte <laforge at osmocom.org>            http://laforge.gnumonks.org/
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