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authorHannes Frederic Sowa <hannes@stressinduktion.org>2014-01-09 10:01:17 +0100
committerDavid S. Miller <davem@davemloft.net>2014-01-13 11:22:55 -0800
commit8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e (patch)
tree4a8093c0dfa1507ce234754a54db8a95399955a4 /Documentation/networking
parent0954cf9c6141d597929a292b93a2dca2c1f29159 (diff)
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ipv4: introduce hardened ip_no_pmtu_disc mode
This new ip_no_pmtu_disc mode only allowes fragmentation-needed errors to be honored by protocols which do more stringent validation on the ICMP's packet payload. This knob is useful for people who e.g. want to run an unmodified DNS server in a namespace where they need to use pmtu for TCP connections (as they are used for zone transfers or fallback for requests) but don't want to use possibly spoofed UDP pmtu information. Currently the whitelisted protocols are TCP, SCTP and DCCP as they check if the returned packet is in the window or if the association is valid. Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: David Miller <davem@davemloft.net> Cc: John Heffner <johnwheffner@gmail.com> Suggested-by: Florian Weimer <fweimer@redhat.com> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation/networking')
-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 0d71fa9..c97932c 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
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