Hi Jason,

Thanks for your response. After the changes you suggested, It still gives me the same problem. Now my GCP server wireguard configuration looks like this.

[Interface]
Address = 192.168.1.1
SaveConfig = true
PostUp = iptables -A FORWARD -i %i -j ACCEPT; iptables -A FORWARD -o %i -j ACCEPT; iptables -t nat -A POSTROUTING -o ens4 -j MASQUERADEi;iptables -t mangle -A POSTROUTING -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -D FORWARD -o %i -j ACCEPT; iptables -t nat -D POSTROUTING -o ens4 -j MASQUERADE
ListenPort = 51840
PrivateKey = <private key>
MTU=1380

[Peer]
PublicKey = <public key>
AllowedIPs = 192.168.1.2/32

On Sun, 9 Feb 2020 at 03:06, Jason A. Donenfeld <Jason@zx2c4.com> wrote:

GCP uses an MTU of 1460 because Google's network does weird things.
That means the MTU for WireGuard should be 1380. On the GCP box, try
adding `MTU=1380` to your config and add this line to PostUp: `
; iptables -t mangle -A POSTROUTING -p tcp --tcp-flags SYN,RST SYN -j
TCPMSS --clamp-mss-to-pmtu`