mcjoin
is a very simple and easy-to-use tool to test IPv4 and IPv6
multicast. it features:
- an optional multicast generator (server)
- an end device that can act as a data sink (client)
- supports joining one or more groups:
- ASM (*,G) support
- SSM (S,G) support
- IPv4
- IPv6
the latest release is always available from GitHub at
https://github.com/troglobit/mcjoin/releases
sender$ mcjoin -s
^C
sender$
without any arguments mcjoin
defaults to an IPv4 ASM (*,G) join of
225.1.2.3
, UDP port 1234
. see the usage section below for more
help.
receiver$ mcjoin
joined group 225.1.2.3 on eth0 ...
..................................................................^C
Received total: 66 packets
receiver$
for testing purposes you may want to use the MCAST_TEST_NET
from
RFC5771, 233.252.0.0/24
, or possibly the ompoing(8) test group
232.43.211.234
, UDP port 4321
, as defined in this IETF draft.
for testing IPv6 you can use ff2e::42
$ mcjoin -h
Usage: mcjoin [-dhjsv] [-c COUNT] [-i IFACE] [-p PORT] [-r SEC] [-t TTL] [-w SEC]
[[SOURCE,]GROUP0 .. [SOURCE,]GROUPN | [SOURCE,]GROUP+NUM]
Options:
-c COUNT Stop sending/receiving after COUNT number of packets
-d Run as daemon in background, output except progress to syslog
-h This help text
-i IFACE Interface to use for sending/receiving multicast, default eth0
-j Join groups, default unless acting as sender
-l LEVEL Set log level; none, notice*, debug\n"
-p PORT UDP port number to listen to, default: 1234
-r SEC Do a join/leave every SEC seconds (backwards compat. option)
-s Act as sender, sends packets to select groups
-t TTL TTL to use when sending multicast packets, default 1
-v Display program version
-w SEC Initial wait before opening sockets
Bug report address: https://github.com/troglobit/mcjoin/issues
Project homepage: https://github.com/troglobit/mcjoin/
the SOURCE
argument is optional, but when used it must be of the same
address family as the group. to join multiple groups, either list them
all on the command line, separated with space, or use the +NUM
syntax.
at the moment max 250 groups can be joined.
the multicast producer, mcjoin -s
, can send without a default route,
but the sink need a default route to be able to receive the UDP stream.
in particular, this issue will arise if you run mcjoin
in isolated
network namespaces in Linux. e.g.
ip netns add sink
ip link set eth2 netns sink
ip netns exec sink /bin/bash
ip address add 127.0.0.1/8 dev lo
ip link set lo up
ip link set eth2 name eth0
ip address add 10.0.0.42/24 dev eth0
ip link set eth0 up
ip route add default via 10.0.0.1
mcjoin
usually there is a limit of 20 group joins per socket in UNIX, this is
the IP_MAX_MEMBERSHIPTS
define. on Linux this can be tweaked using a
/proc
setting:
echo 40 > /proc/sys/net/ipv4/igmp_max_memberships
mcjoin has a different approach, it opens a unique socket per each group
to join and for each socket disables the odd IP_MULTICAST_ALL
socket
option, which is enabled by default. Citing the Linux ip(7)
man page,
emphasis added:
IP_MULTICAST_ALL (since Linux 2.6.31)
This option can be used to modify the delivery policy of multicast messages to sockets bound to the wildcard INADDR_ANY address. The argument is a boolean integer (defaults to 1). If set to 1, the socket will receive messages from all the groups that have been joined globally on the whole system. Otherwise, it will deliver messages only from the groups that have been explicitly joined (for example via the IP_ADD_MEMBERSHIP option) on this particular socket.
hence, by default all multicast applications in UNIX will receive all multicast frames from all groups joined by all other applications on the same system ...
... which IMO is a weird default since multicast by default is opt-in, not opt-out, which is what POSIX makes it. OK, may it's not mandated by POSIX, and (unregulated) multicast is akin to broadcast, but still! I bet most developer's don't know about this.
the GNU Configure & Build system use /usr/local
as the
default install prefix. for most use-cases this is fine, but if you
want to change this to /usr
use the --prefix=/usr
configure option:
$ ./configure --prefix=/usr
$ make -j5
$ sudo make install-strip
if you want to contribute, or simply just try out the latest but unreleased features, then you need to know a few things about the GNU Configure & Build system:
configure.ac
and a per-directoryMakefile.am
are key filesconfigure
andMakefile.in
are generated fromautogen.sh
, they are not stored in GIT but automatically generated for the release tarballsMakefile
is generated byconfigure
script
to build from GIT; clone the repository and run the autogen.sh
script.
this requires automake
and autoconf
to be installed on your system.
(if you build from a released tarball you don't need them.)
git clone https://github.com/troglobit/mcjoin.git
cd mcjoin/
./autogen.sh
./configure && make
sudo make install-strip