radvd,dhcp4: switch to MTU 1280

[1977er]

As a takeaway from last weekends hackathon there is the suggestion to switch to a lower MTU to prevent fragmentation.

Ideas, suggestions, objections?

[lemoer]

There are several things, we should take into account:

• Does a 1280 MTU make sense for wireguard+vxlan? IIRC, 1280 is already a fragmented packet due to the stacking of packet headers...
• We are only talking about UDP, because for TCP, we hopefully have MSS-clamping.
• Most clients are known to ignore the field for udp anyways as I heard.

[1977er]

So, your concern is "it may not help"? I take that as a "lets go". 😉

[AiyionPrime]

At least the first point reads as "it might make things worse".
But if you're talking about "lets go testing" and testing does not happen in prod, I'm totally fine with it.

[AiyionPrime]

Let's not test this in production?

[jue89]

Lowering the MTU to 1280 will make using Wireguard over Freifunk with encapsulated IPv6 impossible.

[1977er]

Shouldn't BATMANs fragging capabilities take care of that?

[jue89]

You're advising clients to lower their MTU to 1280, right?

If they do, you can't use Freifunk to connect to your own Wireguard servers and talk IPv6 over that tunnel.