Provided by: smcroute_2.4.2-4_amd64 
NAME
smcroute — SMCRoute, a static multicast router
SYNOPSIS
smcrouted [-nNhsv] [-c SEC] [-d SEC] [-e CMD] [-f FILE] [-I NAME] [-l LVL] [-p USER:GROUP]
[-P FILE] [-t ID]
smcroutectl [-dtv] [-I NAME] [COMMAND]
smcroutectl ⟨help | flush | kill | restart | version⟩
smcroutectl ⟨show⟩ [groups | routes]
smcroutectl ⟨add | rem⟩ ⟨IFNAME⟩ [SOURCE] GROUP[/LEN] IFNAME [IFNAME ...]
smcroutectl ⟨join | leave⟩ ⟨IFNAME⟩ [SOURCE] GROUP
DESCRIPTION
smcroute is both a daemon and command line tool to manipulate the multicast routing table of
a UNIX kernel. It supports both IPv4 and IPv6 multicast routing. smcroute can be used as
an alternative to dynamic multicast routers like mrouted or pimd in situations where static
multicast routes should be maintained and/or no proper IGMP or MLD signaling exists.
Multicast routes exist in the UNIX kernel as long as a multicast routing daemon is running.
On Linux, multiple multicast routers can be used simultaneously with different multicast
routing tables. To run smcrouted and, mrouted at the same time, set the former to use a
routing table other than the default (0).
smcrouted modifies the kernel routing table and needs either full superuser rights, or
CAP_NET_ADMIN on Linux. This also applies to smcroutectl.
WARNING
Be careful when creating multicast routes. You can easily flood your networks by
inadvertently creating routing loops. Either direct loops listing an inbound interface also
as an outbound, or indirect loops by going through other routers.
OPTIONS
The following smcrouted commands are available:
-n Run daemon in foreground, do not detach from controlling terminal
-N By default smcrouted enables multicast routing on all available, and multicast
capable, interfaces in the system. These interfaces are enumerated as VIFs, virtual
interfaces, of which most UNIX systems have a very limited amount, usually 32. This
daemon option inverts the behavior so no interfaces are enabled by default. Useful
on systems with many interfaces, where multicast routing only makes use of a few.
The config file setting phyint IFNAME enable is required to enable the required
interfaces.
-f FILE
Alternate configuration file, default /etc/smcroute.conf
-c SEC Flush unused dynamic (*,G) multicast routes every SEC seconds.
This option is intended for systems with topology changes, i.e., when inbound
multicast may change both interface and source IP address. E.g. in a setup with at
least two VRRP routers. If there is no way of detecting such a topology change this
option makes sure to periodically flush all dynamically learned multicast routes so
that traffic may resume. Flushing of a specific route only occurs if it was unused
during the last flush interval, i.e. there was no traffic matching it. This avoids
toggling between different inbound interfaces if traffic arrives on several
interfaces simultaneously. In this case, the first selected inbound interface is
retained until traffic on it ceases.
Default is 60 sec, set to 0 to disable. See also the smcroutectl flush command,
which can be called manually on topology changes.
-d SEC Daemon startup delay. Delays the probe of interfaces and parsing of the
configuration file. Note, the PID file is also not created, since the daemon is not
ready yet.
This command line option, although useful in some use-cases, is fragile. It is
almost always better to rely on an init or process supervisor that handles
dependencies properly, like finit(8), which can wait for interfaces to come up and
files to be created before starting a service.
-e CMD Specify external script or command to be called when smcrouted has loaded/reloaded
all static multicast routes from the configuration file, or when a source-less (ANY)
rule has been installed.
-I NAME
Set daemon identity. Used to create unique PID, IPC socket, and configuration file
names, as well as set the syslog identity. E.g., -I foo would make smcrouted look
for /etc/foo.conf, write its PID to /var/run/foo.pid and create an IPC socket for
smcroutectl in /var/run/foo.sock.
For smcroutectl the same option can be used to select the proper smcrouted instance
to send IPC to.
This option is required for both daemon and client when running multiple smcrouted
instances, using multiple routing tables, on Linux.
-l LEVEL
Set log level: none, err, notice, info, debug. Default is notice.
-p USER [:GROUP]
Drop root privileges to USER:GROUP after start and retain CAP_NET_ADMIN capabilities
only. The :GROUP is optional. This option is only available when smcrouted is
built with libcap support.
-P FILE
Set PID file name, and optionally full path, in case you need to override the
default identity, or the identity set with -I NAME. Regardless, setting this option
overrides all others, but it is recommended to use the ident option instead.
-s Let daemon log to syslog, default unless running in foreground.
-t ID Set multicast routing table ID. Remember to also create routing rules directing
packets to the table. This example uses routing table ID 123:
ip mrule add iif eth0 lookup 123
ip mrule add oif eth0 lookup 123
Note: Only available on Linux.
-v Show program version.
The -e CMD option is useful if you want to trigger other processes to start when smcrouted
has completed installing dynamic multicast routes from (*,G) rules in /etc/smcroute.conf, or
when a source-less (ANY) route, a.k.a (*,G) multicast rule, from /etc/smcroute.conf. is
matched and installed. For instance, calling conntrack on Linux to flush firewall
connection tracking when NAT:ing multicast.
The script CMD is called with an argument reload or install to let the script know if it is
called on SIGHUP/startup, or when a (*,G) rule is matched and installed. In the latter case
smcrouted also sets two environment variables: source, and group. Beware that these
environment variables are unconditionally overwritten by smcrouted and can thus not be used
to pass information to the script from outside of smcrouted.
COMMANDS
The IFNAME argument in the below smcroutectl commands is the interface name, or an interface
wildcard of the form eth+, which matches eth0, eth10, etc. Wildcards are available for
inbound interfaces. The following commands are available:
add IFNAME [SOURCE] GROUP[/LEN] OUTIFNAME [OUTIFNAME ...]
Add a multicast route to the kernel routing cache so that multicast packets received
on the network interface IFNAME originating from the IP address SOURCE and sent to
the multicast group address GROUP will be forwarded to the outbound network
interfaces OUTIFNAME [OUTIFNAME ...]. The interfaces provided as INIFNAME and
OUTIFNAME can be any network interface as listed by 'ifconfig' or 'ip link list'
(incl. tunnel interfaces), but not the loopback interface.
To add a (*,G) route, either leave SOURCE out completely or set it to 0.0.0.0, and
if you want to specify a range, set GROUP/LEN, e.g. 225.0.0.0/24.
remove IFNAME [SOURCE] GROUP
Remove a kernel multicast route.
flush Flush dynamic (*,G) multicast routes now. Similar to how -c SEC works in the
daemon, this client command initiates an immediate flush of all dynamically set
(*,G) routes. Useful when a topology change has been detected and need to be
propagated to smcrouted.
join IFNAME [SOURCE] GROUP
Join a multicast group on a given interface. The source address is optional, but if
given a source specific (SSM) join is performed.
leave IFNAME [SOURCE] GROUP
Leave a multicast group on a given interface. As with the join command, above, the
source address is optional.
help [cmd]
Print a usage information message.
kill Stop (kill) running daemon.
restart
Tell daemon to restart and reload its configuration file. Same as SIGHUP.
show [groups|routes]
Show joined multicast groups or multicast routes, defaults to show routes. Can be
combined with the -d option to get details for each multicast route.
version
Show program version.
A multicast route is defined by an input interface IFNAME, the sender's unicast IP address
SOURCE, which is optional, the multicast group GROUP and a list of, at least one, output
interface IFNAME [IFNAME ...].
The sender's address and the multicast group must both be either IPv4 or IPv6 addresses.
The output interfaces are not needed when removing routes using the remove command. The
first three parameters are sufficient to identify the source of the multicast route.
The intended purpose of smcroute is to aid in situations where dynamic multicast routing
does not work properly. However, a dynamic multicast routing protocol is in nearly all
cases the preferred solution. The reason for this is their ability to translate Layer-3
signaling to Layer-2 and vice versa (IGMP or MLD).
smcrouted is capable of simple group join and leave by sending commands to the kernel. The
kernel then handles sending Layer-2 IGMP/MLD join and leave frames as needed. This can be
used for testing but is also useful sometimes to open up multicast from the sender if
located on a LAN with switches equipped with IGMP/MLD Snooping. Such devices will prevent
forwarding of multicast unless an IGMP/MLD capable router or multicast client is located on
the same physical port as you run smcrouted on. However, this feature of smcrouted is only
intended as a workaround, and only 20 groups can be joined this way (kernel limit). For
bigger installations it is strongly recommended to instead address the root cause, e.g.
enable multicast router ports on intermediate switches, or try the embedded multicast router
discovery feature of smcrouted.
To emulate a multicast client using smcroute you use the join and leave commands to issue
join and leave commands for a given multicast group on a given interface IFNAME. The GROUP
may be given in an IPv4 or IPv6 address format.
The command is passed to the daemon that passes it to the kernel. The kernel then tries to
join the multicast group GROUP on interface IFNAME by starting IGMP, or MLD for IPv6 group
address, signaling on the given interface. This signaling may be received by
routers/switches connected on that network supporting IGMP/MLD multicast signaling and, in
turn, start forwarding the requested multicast stream eventually reach your desired
interface.
Note: when running multiple smcrouted instances, one per routing table on Linux, it is
required to use the -I NAME option to both daemon and client. This because the name of the
IPC socket used for communicating is composed from the identity.
CONFIGURATION FILE
smcrouted supports reading and setting up multicast routes from a config file. The default
location is /etc/smcroute.conf, but this can be overridden using the -f FILE command line
option.
The IFNAME argument below is the interface name, or an interface wildcard of the form eth+,
which matches eth0, eth10, etc. Wildcards are available for inbound interfaces.
#
# smcroute.conf example
#
# The configuration file supports joining multicast groups, to use
# Layer-2 signaling so that switches and routers open up multicast
# traffic to your interfaces. Leave is not supported, remove the
# mgroup and SIGHUP your daemon, or send a specific leave command.
#
# NOTE: Use of the mgroup command should be avoided if possible.
# Instead configure "router ports" or similar on the switches
# or bridges on your LAN. This to have them direct all the
# multicast to your router, or direct select groups they have
# such capabilities. Usually MAC multicast filters exist.
#
# The UNIX kernel usually limits the number of multicast groups
# a socket/client can join. In Linux, 20 mgroup lines can be
# configured by default, but this can be changed with sysctl:
#
# sysctl -w net.ipv4.igmp_max_memberships=30
#
# Similarly supported is setting mroutes. Removing mroutes is not
# supported, remove/comment out the mroute from the .conf file, or
# send a remove command with smcroutectl.
#
# Syntax:
# phyint IFNAME <enable|disable> [mrdisc] [ttl-threshold <1-255>]
# mgroup from IFNAME [source ADDRESS] group MCGROUP
# mroute from IFNAME [source ADDRESS] group MCGROUP[/LEN] to IFNAME [IFNAME ...]
# This example disables the creation of a multicast VIF for WiFi
# interface wlan0. The kernel (at least Linux) sets the ALLMULTI
# flag for all interfaces that have a VIF enabled. Hence, it can
# cause quite a bit of unnecessary traffic to reach the CPU if too
# many interfaces have a VIF (or MIF in IPv6 lingo). Only enable
# interfaces required for inbound and outbound traffic.
# phyint wlan0 disable
phyint eth0 enable ttl-threshold 11
phyint eth1 enable ttl-threshold 3
phyint eth2 enable ttl-threshold 5
phyint virbr0 enable ttl-threshold 5
# The following example instructs the kernel to join the multicast
# group 225.1.2.3 on interface eth0. Followed by setting up an
# mroute of the same multicast stream, but from the explicit sender
# 192.168.1.42 on the eth0 network and forward to eth1 and eth2.
#
mgroup from eth0 group 225.1.2.3
mroute from eth0 source 192.168.1.42 group 225.1.2.3 to eth1 eth2
# Similar example, but using source-specific group join
mgroup from virbr0 source 192.168.123.110 group 225.1.2.4
mroute from virbr0 source 192.168.123.110 group 225.1.2.4 to eth0
# Here we allow routing of multicast to group 225.3.2.1 from ANY
# source coming in from interface eth0 and forward to eth1 and eth2.
# NOTE: Routing from ANY source is currently only available for IPv4
# multicast.
mgroup from eth0 group 225.3.2.1
mroute from eth0 group 225.3.2.1 to eth1 eth2
# The previous is an example of the (*,G) support. Such rules cause
# SMCRoute to dynamically add multicast routes to the kernel when the
# first frame of a stream reaches the router. It is also possible to
# specify a range of such rules, again, note that this currently only
# works for IPv4. Also, it is not possible to set a range of groups
# to join atm.
mroute from eth0 group 225.0.0.0/24 to eth1 eth2
Fairly simple. As usual, to identify the origin of the inbound multicast we need the IFNAME,
the sender's IP address and, of course, the multicast group address, MCGROUP. The last
argument is a list of outbound interfaces.
The source address is optional for IPv4 multicast routes. If omitted it defaults to 0.0.0.0
(INADDR_ANY) and will cause smcrouted to dynamically add new routes, matching the group and
inbound interface, to the kernel. This is an experimental feature which may not work as
intended, in particular not with 1:1 NAT.
Following the UNIX tradition the file format supports comments starting at the beginning of
the line using a hash sign. It is untested to have comments at the end of a line, but
should work.
When starting up in debug mode, smcrouted logs the success of parsing each line and setting
up a route.
LIMITS
The current version compiles and runs fine on Linux kernel version 2.4, 2.6 and 3.0. Known
limits:
Multicast routes
Depends on the kernel, more than 200, probably more than 1000
Multicast group memberships
Max. 20, see caveat above
SIGNALS
smcrouted responds to the following signals:
HUP Restart and reload the configuration file. All existing multicast routes and groups
are dropped.
INT Terminates execution gracefully.
TERM The same as INT.
For convenience in sending signals, smcrouted writes its process ID to /var/run/smcroute.pid
upon startup.
DEBUGGING
The most common problem when attempting to route multicast is the TTL. Always start by
verifying that the TTL of your multicast stream is not set to 1, because the router
decrements the TTL of an IP frame before routing it. Test your setup using ping(8) or
iperf(1). Either of which is capable of creating multicast traffic with an adjustable TTL.
Iperf in particular is useful since it can act both as a multicast source (sender) and a
multicast sink (receiver). For more advanced IP multicast testing the omping(8) tool can be
used.
FILES
/etc/smcroute.conf Routes to be set when starting, or restarting smcrouted on SIGHUP.
Like the PID file, the name of the configuration file may be
different depending on command line options given to the daemon.
/var/run/smcroute.pid Default PID file (re)created by smcrouted when it has started up and
is ready to receive commands. See also the -I NAME or -P FILE
options which can change the default name.
/var/run/smcroute.sock IPC socket created by smcrouted for use by smcroutectl. Same
caveats apply to this file as the previous two, command line options
to the daemon can change the file names.
/proc/net/ip_mr_cache Holds active IPv4 multicast routes.
/proc/net/ip_mr_vif Holds the IPv4 virtual interfaces used by the active multicast
routing daemon.
/proc/net/ip6_mr_cache Holds active IPv6 multicast routes.
/proc/net/ip6_mr_vif Holds the IPv6 virtual interfaces used by the active multicast
routing daemon.
/proc/net/igmp Holds active IGMP joins.
/proc/net/igmp6 Holds active MLD joins.
SEE ALSO
mrouted(8), pimd(8), omping(8), ping(8), mcjoin(1), iperf(1)
AUTHORS
SMCRoute was created by Carsten Schill <carsten@cschill.de>. IPv6 support by Todd Hayton
<todd.hayton@gmail.com>. FreeBSD support by Micha Lenk <micha@debian.org>.
smcrouted is maintained by Joachim Nilsson <troglobit@gmail.com>, Todd Hayton
<todd.hayton@gmail.com>, Micha Lenk <micha@debian.org> and Julien BLACHE
<jblache@debian.org> at https://github.com/troglobit/smcroute
TIPS
A lot of extra information is sent under the daemon facility and the debug priority to the
syslog daemon. Use smcrouted -s -l debug to enable.