1This target allows to alter the MSS value of TCP SYN packets, to control
2the maximum size for that connection (usually limiting it to your
3outgoing interface's MTU minus 60).  Of course, it can only be used
4in conjunction with
5.BR "-p tcp" .
6It is only valid in the
7.BR mangle
8table.
9.br
10This target is used to overcome criminally braindead ISPs or servers
11which block ICMPv6 Packet Too Big packets or are unable to send them.
12The symptoms of this problem are that everything works fine from your 
13Linux firewall/router, but machines behind it can never exchange large
14packets:
15.PD 0
16.RS 0.1i
17.TP 0.3i
181)
19Web browsers connect, then hang with no data received.
20.TP
212)
22Small mail works fine, but large emails hang.
23.TP
243)
25ssh works fine, but scp hangs after initial handshaking.
26.RE
27.PD
28Workaround: activate this option and add a rule to your firewall
29configuration like:
30.nf
31 ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN \\
32             -j TCPMSS --clamp-mss-to-pmtu
33.fi
34.TP
35.BI "--set-mss " "value"
36Explicitly set MSS option to specified value.
37.TP
38.B "--clamp-mss-to-pmtu"
39Automatically clamp MSS value to (path_MTU - 60).
40.TP
41These options are mutually exclusive.
42