diff options
| author | Jeremy Eder <jeder@redhat.com> | 2010-11-15 05:41:31 +0000 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2010-11-17 11:22:06 -0800 |
| commit | d67ef35fff67845c64d806c033cc7c569ccebfff (patch) | |
| tree | 4dea9054aa80cdb0b9c4a3a020aa11509f60bf72 /Documentation/networking | |
| parent | 9920239c90d5f6dadfb44325abf3568a5e3fd827 (diff) | |
clarify documentation for net.ipv4.igmp_max_memberships
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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation/networking')
| -rw-r--r-- | Documentation/networking/ip-sysctl.txt | 24 |
1 files changed, 21 insertions, 3 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index fe95105992c5..ae5522703d16 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. |