iptables clamp-mss-to-pmtu

Hi,

I'm on ADSL and  !important]Netalyzr claims I can't send fragmented UDP traffic, that is, until I move the clamp-mss-to-pmtu rule to the mangle table.

I have the following firewall-start script which fixes the problem:

1. #!/bin/sh
   
2. iptables -D FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
   
3. iptables -t mangle -A POSTROUTING -p tcp --tcp-flags SYN,RST SYN -j TCPMSS -o ppp0 --clamp-mss-to-pmtu

复制代码

OpenWRT decided to move the rule to the mangle table. There are a few OpenWRT discussions about this. Now, putting the rule in FORWARD or POSTROUTING seems to be a great debate, but in my case, fixed some things.

https://lists.openwrt.org/piperm ... ebruary/014129.html

Netalyzr is also claiming that ICMP too big packets are blocked, which could explain why the fix is necessary to start with. Is there a ICMP blocking rule on Asuswrt or (most probably) my ISP is blocking them?