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

[OpenWrt Bugs]

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A new Flyspray task has been opened.  Details are below. 

User who did this - Weikai Zhang (weikai) 

Attached to Project - OpenWrt/LEDE Project
Summary - OpenVPN Client Using TCP Connection Has MTU or TCPMSS Issue
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Medium
Priority - Very Low
Reported Version - openwrt-21.02
Due in Version - Undecided
Due Date - Undecided
Details - 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

More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=3830

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