From: Jeremy Eder <jeder@redhat.com>
To: netdev@vger.kernel.org
Cc: rdunlap@xenotime.net, davem@davemloft.net, opurdila@ixiacom.com,
apetlund@simula.no, William.Allen.Simpson@gmail.com,
ian.campbell@citrix.com, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, Jiri Pirko <jpirko@redhat.com>
Subject: [PATCH net-next-2.6] clarify documentation for net.ipv4.igmp_max_memberships
Date: Mon, 15 Nov 2010 10:41:31 -0500 [thread overview]
Message-ID: <1289835691.8257.1274.camel@jerms-wks.usersys.redhat.com> (raw)
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.
next reply other threads:[~2010-11-15 15:42 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-15 15:41 Jeremy Eder [this message]
2010-11-17 19:22 ` [PATCH net-next-2.6] clarify documentation for net.ipv4.igmp_max_memberships David Miller
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1289835691.8257.1274.camel@jerms-wks.usersys.redhat.com \
--to=jeder@redhat.com \
--cc=William.Allen.Simpson@gmail.com \
--cc=apetlund@simula.no \
--cc=davem@davemloft.net \
--cc=ian.campbell@citrix.com \
--cc=jpirko@redhat.com \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=opurdila@ixiacom.com \
--cc=rdunlap@xenotime.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).