Documentation: fix outdated interpretation of ip_no_pmtu_disc

The updating way of pmtu has changed, but documentation is still in the
old way. So this patch updates the interpretation of ip_no_pmtu_disc and
min_pmtu.

See commit 28d35bcdd3925 ("net: ipv4: don't let PMTU updates increase
route MTU")

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index c044311..2572eec 100644 (file)
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -25,7 +25,8 @@ ip_default_ttl - INTEGER
 ip_no_pmtu_disc - INTEGER
        Disable Path MTU Discovery. If enabled in mode 1 and a
        fragmentation-required ICMP is received, the PMTU to this
-       destination will be set to min_pmtu (see below). You will need
+       destination will be set to the smallest of the old MTU to
+       this destination and min_pmtu (see below). You will need
        to raise min_pmtu to the smallest interface MTU on your system
        manually if you want to avoid locally generated fragments.
 
@@ -49,7 +50,8 @@ ip_no_pmtu_disc - INTEGER
        Default: FALSE
 
 min_pmtu - INTEGER
-       default 552 - minimum discovered Path MTU
+       default 552 - minimum Path MTU. Unless this is changed mannually,
+       each cached pmtu will never be lower than this setting.
 
 ip_forward_use_pmtu - BOOLEAN
        By default we don't trust protocol path MTUs while forwarding