Merge branch 'drm-core-next' of git://git.kernel.org/pub/scm/linux/kernel/git/airlied...

[karo-tx-linux.git] / Documentation / networking / ip-sysctl.txt

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 3c5e465296e146b3089adfcec06f6c96c9805ddb..d99940dcfc442c7a3ae5e209c0eef4af99d3d876 100644 (file)
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -11,7 +11,9 @@ ip_forward - BOOLEAN
        for routers)
 
 ip_default_ttl - INTEGER
-       default 64
+       Default value of TTL field (Time To Live) for outgoing (but not
+       forwarded) IP packets. Should be between 1 and 255 inclusive.
+       Default: 64 (as recommended by RFC1700)
 
 ip_no_pmtu_disc - BOOLEAN
        Disable Path MTU Discovery.
@@ -708,10 +710,28 @@ igmp_max_memberships - INTEGER
        Change the maximum number of multicast groups we can subscribe to.
        Default: 20
 
-conf/interface/*  changes special settings per interface (where "interface" is
-                 the name of your network interface)
-conf/all/*       is special, changes the settings for all interfaces
+       Theoretical maximum value is bounded by having to send a membership
+       report in a single datagram (i.e. the report can't span multiple
+       datagrams, or risk confusing the switch and leaving groups you don't
+       intend to).
 
+       The number of supported groups 'M' is bounded by the number of group
+       report entries you can fit into a single datagram of 65535 bytes.
+
+       M = 65536-sizeof (ip header)/(sizeof(Group record))
+
+       Group records are variable length, with a minimum of 12 bytes.
+       So net.ipv4.igmp_max_memberships should not be set higher than:
+
+       (65536-24) / 12 = 5459
+
+       The value 5459 assumes no IP header options, so in practice
+       this number may be lower.
+
+       conf/interface/*  changes special settings per interface (where
+       "interface" is the name of your network interface)
+
+       conf/all/*        is special, changes the settings for all interfaces
 
 log_martians - BOOLEAN
        Log packets with impossible addresses to kernel log.