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