OpenWrt/LEDE Project

  • Status Unconfirmed
  • Percent Complete
  • Task Type Bug Report
  • Category Base system
  • Assigned To No-one
  • Operating System All
  • Severity Medium
  • Priority Very Low
  • Reported Version openwrt-21.02
  • Due in Version Undecided
  • Due Date Undecided
  • Private
Attached to Project: OpenWrt/LEDE Project
Opened by Weikai Zhang - 26.05.2021

FS#3830 - OpenVPN Client Using TCP Connection Has MTU or TCPMSS Issue

OpenVPN Client connects to a TCP based OpenVPN server connects fine. However, the connections to remote network servers connect but can’t transfer data. The mangle rule with clamp-mss-to-pmtu won’t receive any data. Setting tcpmss to something around 1000 will only receive the first 100 - 200 bytes and hang. It’s not working until reduced tcpmss to 59.

iptables -t nat -A postrouting_rule -o tun0 -j MASQUERADE
iptables -t mangle -A POSTROUTING -o tun0 -p tcp -m tcp –tcp-flags SYN,RST SYN -j TCPMSS –set-mss 59
#iptables -t mangle -A POSTROUTING -o tun0 -p tcp -m tcp –tcp-flags SYN,RST SYN -j TCPMSS –clamp-mss-to-pmtu


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