path: root/extensions/
diff options
authorHenrik Nordstrom <>2004-01-22 15:04:24 +0000
committerHarald Welte <>2004-01-22 15:04:24 +0000
commitc2794131b445ebccba184066af6d3fb2f38d1f38 (patch)
treea24f57a9be5a8364b53dfa102705d270f36b440a /extensions/
parent0113fe75ff05e09e6f3d251534d9ae32e9aa717c (diff)
split manpages into per-extension manpage snippet (Henrik Nordstrom)
add lots of missing manpage snippets (Harald Welte)
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1 files changed, 38 insertions, 0 deletions
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+This target allows to alter the MSS value of TCP SYN packets, to control
+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
+.BR "-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
+.PD 0
+.RS 0.1i
+.TP 0.3i
+Web browsers connect, then hang with no data received.
+Small mail works fine, but large emails hang.
+ssh works fine, but scp hangs after initial handshaking.
+Workaround: activate this option and add a rule to your firewall
+configuration like:
+ iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \\
+ -j TCPMSS --clamp-mss-to-pmtu
+.BI "--set-mss " "value"
+Explicitly set MSS option to specified value.
+.B "--clamp-mss-to-pmtu"
+Automatically clamp MSS value to (path_MTU - 40).
+These options are mutually exclusive.