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-rw-r--r--Documentation/networking/ip-sysctl.txt13
1 files changed, 12 insertions, 1 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 0d71fa962d8a..c97932c88ea3 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -26,7 +26,18 @@ ip_no_pmtu_disc - INTEGER
discarded. Outgoing frames are handled the same as in mode 1,
implicitly setting IP_PMTUDISC_DONT on every created socket.
- Possible values: 0-2
+ Mode 3 is a hardend pmtu discover mode. The kernel will only
+ accept fragmentation-needed errors if the underlying protocol
+ can verify them besides a plain socket lookup. Current
+ protocols for which pmtu events will be honored are TCP, SCTP
+ and DCCP as they verify e.g. the sequence number or the
+ association. This mode should not be enabled globally but is
+ only intended to secure e.g. name servers in namespaces where
+ TCP path mtu must still work but path MTU information of other
+ protocols should be discarded. If enabled globally this mode
+ could break other protocols.
+
+ Possible values: 0-3
Default: FALSE
min_pmtu - INTEGER