path: root/extensions
diff options
authorTim Small <>2009-10-16 20:00:04 +0100
committerHarald Welte <>2009-10-25 10:58:23 +0100
commit22bdd6966f2c3ccded984a37ba0b97470bcf9323 (patch)
tree67837effd91fc49bb45733c2f84c481edf627503 /extensions
parent94aa2ea67d7b8a669e8541f094661a1dc89722a3 (diff)
doc: update TCPMSS manpage with Linux 2.6.25 changes
References: [j.eng: modified --set-mss option description to be understandable] Signed-off-by: Jan Engelhardt <>
Diffstat (limited to 'extensions')
1 files changed, 9 insertions, 1 deletions
diff --git a/extensions/ b/extensions/
index dbab918d..b5cb455f 100644
--- a/extensions/
+++ b/extensions/
@@ -34,9 +34,17 @@ configuration like:
\-j TCPMSS \-\-clamp\-mss\-to\-pmtu
\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.
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.
These options are mutually exclusive.