Help calculate MTU, ISP's 1448

[Derrick Lyndon Pallas]

I've had to drop to 1280 from Linode to several cellular carriers or else IPv6 fails. Ymmv, but the primary problem I've seen is MTU discovery failing because the v6 message is being eaten but not the v4 message. Have you enabled discovery in the kernel?

~Derrick • iPhone

> On Feb 28, 2019, at 11:56 AM, Denis Kisselev <denis at dkisselev.net> wrote:
> 
> Check what IP's the google domains are resolving to.
> 
> You might be getting IPv6 DNS responses back and your VPN/firewall configuration is blocking them.
> I've run into the opposite issue where my ISP's IPv4 stack crashed and Google/Facebook worked (over IPv6) but most other sites failed.
> From: WireGuard <wireguard-bounces at lists.zx2c4.com> on behalf of STR . <strykar at hotmail.com>
> Sent: Tuesday, February 26, 2019 4:39 AM
> To: wireguard at lists.zx2c4.com
> Subject: Help calculate MTU, ISP's 1448
>  
> Hi,
> 
> I have Fiber to our apartment complex basement, from there Cat6 runs to
> each apartment. The ISP/apartment service provider suggests an MTU of
> 1448, which I set for the PPPoE interface on my OpenWRT router.
> 
> I read 
> https://lists.zx2c4.com/pipermail/wireguard/2017-December/002201.html
> which comes to (assuming 1500 byte MTU) to 60 bytes (IPv6) to 80 bytes less to account for Wireguard protocol overhead.
> 
> Using this info, I tried an MTU of both (1448-80=1368) and (1448-
> 60=1388).
> As my ISP assigns only IPv4, I expected an MTU of 1388 to work, which I
> set on the Wireguard interface in OpenWRT.
> 
> However, when set to 1388, almost everything works except any Google
> related sites like Maps, Gmail, YT etc.
> When set to 1368, everything works and it's the way I have it setup
> right now.
> 
> What am I missing here?
> Why won't Google sites load via my WG VPN when the MTU is set to 1388?
> 
> If it helps, I host the WG server on Google's cloud platform and was
> informed that GCP has an MTU of 1460 bytes.
> 
> Thank you,
> S
> 
> _______________________________________________
> WireGuard mailing list
> WireGuard at lists.zx2c4.com
> https://lists.zx2c4.com/mailman/listinfo/wireguard
> _______________________________________________
> WireGuard mailing list
> WireGuard at lists.zx2c4.com
> https://lists.zx2c4.com/mailman/listinfo/wireguard
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.zx2c4.com/pipermail/wireguard/attachments/20190228/becc8f2b/attachment.html>