Merge tag 'v2.6.38' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6

[mv-sheeva.git] / Documentation / networking / ip-sysctl.txt

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 3c5e465296e146b3089adfcec06f6c96c9805ddb..ac3b4a726a1a70b439abf72922d1db0791e78ae8 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.
@@ -185,7 +187,7 @@ tcp_cookie_size - INTEGER
 tcp_dsack - BOOLEAN
        Allows TCP to send "duplicate" SACKs.
 
-tcp_ecn - BOOLEAN
+tcp_ecn - INTEGER
        Enable Explicit Congestion Notification (ECN) in TCP. ECN is only
        used when both ends of the TCP flow support it. It is useful to
        avoid losses due to congestion (when the bottleneck router supports
@@ -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.