passing-through TOS/DSCP marking

[Daniel Golle]

Hi Jason,

On Wed, Jun 16, 2021 at 06:28:12PM +0200, Jason A. Donenfeld wrote:
> WireGuard does not copy the inner DSCP mark to the outside, aside from
> the ECN bits, in order to avoid a data leak.

That's a very valid argument.

However, from my experience now, Wireguard is not suitable for VoIP/RTP
data (minimize-delay) being sent through the same tunnel as TCP bulk
(maximize-throughput) traffic in bandwidth constraint and/or high-latency
environments, as that ruins the VoIP calls to the degree of not being
understandable. ECN helps quite a bit when it comes to avoid packet drops
for TCP traffic, but that's not enough to avoid high jitter and drops for
RTP/UDP traffic at the same time.

I thought about ways to improve that and wonder what you would suggest.
My ideas are:
 * have different tunnels depending on inner DSCP bits and mark them
   accordingly on the outside.
   => we already got multiple tunnels and that would double the number.

 * mark outer packets with DSCP bits based on their size.
   VoIP RTP/UDP packets are typically "medium sized" while TCP packets
   typically max out the MTU.
   => we would not leak information, but that assumption may not always
      be true

 * patch wireguard kernel code to allow preserving inner DSCP bits.
   => even only having 2 differentl classes of traffic (critical vs.
      bulk) would already help a lot...


What do you think? Any other ideas?


Cheers


Daniel