doc: update TCPMSS manpage with Linux 2.6.25 changes

References: http://bugs.debian.org/551272

[j.eng: modified --set-mss option description to be understandable]

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>

diff --git a/extensions/libxt_TCPMSS.man b/extensions/libxt_TCPMSS.man
index dbab918d76b8416cb75e23034a69a92838593a85..b5cb455f10bd5ff063488ec236ef1428a407211d 100644 (file)
--- a/extensions/libxt_TCPMSS.man
+++ b/extensions/libxt_TCPMSS.man
@@ -34,9 +34,17 @@ configuration like:
              \-j TCPMSS \-\-clamp\-mss\-to\-pmtu
 .TP
 \fB\-\-set\-mss\fP \fIvalue\fP
-Explicitly set MSS option to specified value.
+Explicitly sets MSS option to specified value. If the MSS of the packet is
+already lower than \fIvalue\fP, it will \fBnot\fP be increased (from Linux
+2.6.25 onwards) to avoid more problems with hosts relying on a proper MSS.
 .TP
 \fB\-\-clamp\-mss\-to\-pmtu\fP
 Automatically clamp MSS value to (path_MTU \- 40 for IPv4; \-60 for IPv6).
+This may not function as desired where asymmetric routes with differing
+path MTU exist \(em the kernel uses the path MTU which it would use to send
+packets from itself to the source and destination IP addresses. Prior to
+Linux 2.6.25, only the path MTU to the destination IP address was
+considered by this option; subsequent kernels also consider the path MTU
+to the source IP address.
 .PP
 These options are mutually exclusive.