I use VMWare player with MikroTik 3.22 and PPtP over PPPoE to connect to the Internet. Most sites works fine, but some of them freeze. I set PPtP MTU 1450 and PPPoE MTU 1492. As I understand Mikrotik automatic ip firewall mangle rule for my PPtP MTU seems like following “iptables -t mangle -A FORWARD -o Iface_PPtP -p tcp -m tcp --tcp-flags SYN -m tcpmss --mss 1411:65535 -j TCPMSS --set-mss 1410”.
I tried to use MicroTik “-j TCPMSS --clamp-mss-to-pmtu” ip firewall mangle rule but still had the same problem with some sites.
But when I replaced Mikrotik automatic ip firewall mangle rule with alike rule but manually set “j TCPMSS --set-mss 1406” all the sites work fine.
Why Mikrotik automatic ip firewall mangle rule works incorrectly?
P.S. From the PPtP server’s side (pptpd on ubuntu server) I see following link parameters:
ppp3 Link encap: Protocol PPP (Point-to-Point Protocol)
inet addr:192.168.2.3 P-t-P:192.168.2.50 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1446 Metric:1