* [PATCH net-next-2.6] clarify documentation for net.ipv4.igmp_max_memberships
@ 2010-11-15 15:41 Jeremy Eder
2010-11-17 19:22 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Jeremy Eder @ 2010-11-15 15:41 UTC (permalink / raw)
To: netdev
Cc: rdunlap, davem, opurdila, apetlund, William.Allen.Simpson,
ian.campbell, linux-doc, linux-kernel, Jiri Pirko
This patch helps clarify documentation for
net.ipv4.igmp_max_memberships by providing a formula for
calculating the maximum number of multicast groups that can be
subscribed to, plus defining the theoretical limit.
Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: Jeremy Eder <jeder@redhat.com>
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index fe95105..ae55227 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -707,10 +707,28 @@ 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.
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH net-next-2.6] clarify documentation for net.ipv4.igmp_max_memberships
2010-11-15 15:41 [PATCH net-next-2.6] clarify documentation for net.ipv4.igmp_max_memberships Jeremy Eder
@ 2010-11-17 19:22 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2010-11-17 19:22 UTC (permalink / raw)
To: jeder
Cc: netdev, rdunlap, opurdila, apetlund, William.Allen.Simpson,
ian.campbell, linux-doc, linux-kernel, jpirko
From: Jeremy Eder <jeder@redhat.com>
Date: Mon, 15 Nov 2010 10:41:31 -0500
> This patch helps clarify documentation for
> net.ipv4.igmp_max_memberships by providing a formula for
> calculating the maximum number of multicast groups that can be
> subscribed to, plus defining the theoretical limit.
>
> Signed-off-by: Jiri Pirko <jpirko@redhat.com>
> Signed-off-by: Jeremy Eder <jeder@redhat.com>
Applied, thanks Jeremy.
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