--mss value[:value]
Match TCP SYN or SYN/ACK packets with the specified MSS value
(or range), which control the maximum packet size for that con-
nection.
TCPMSS
This target allows to alter the MSS value of TCP SYN packets, to con-
trol the maximum size for that connection (usually limiting it to your
outgoing interface's MTU minus 40). Of course, it can only be used in
conjunction with -p tcp.
This target is used to overcome criminally braindead ISPs or servers
which block ICMP Fragmentation Needed packets. The symptoms of this
problem are that everything works fine from your Linux firewall/router,
but machines behind it can never exchange large packets:
1) Web browsers connect, then hang with no data received.
2) Small mail works fine, but large emails hang.
3) ssh works fine, but scp hangs after initial handshaking.
Workaround: activate this option and add a rule to your firewall con-
figuration like:
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
-j TCPMSS --clamp-mss-to-pmtu
|Dear all,
|
|I found this command in the HOWTO:
|
|iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 128
|
|It resolve (almost) all my problems with the voip traffic on my linux-based
|router.
|The question is: What does it make exactly? It is safe to use it?
|
|Thanks for your attention,