That kind of problems is usually caused by over-active network admins that block all ICMP and thus kill PMTU discovery. You can work around it by doing "TCP MSS clamping" at your end. E.g. when you have a MikroTik router: /ip firewall mangle add action=change-mss chain=forward new-mss=clamp-to-pmtu passthrough=yes \ protocol=tcp tcp-flags=syn Rob