NAME

smcroute —

SMCRoute, a static multicast router

SYNOPSIS

smcroute [dnkhv] [-f FILE] [-e CMD] [-L LVL] [-a|-r ROUTE] [-j|-l GROUP]

DESCRIPTION

smcroute is a command line tool to manipulate the multicast routes 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.

Generally multicast routes exists in the kernel only as long as smcroute or another multicast routing daemon is running. Only one multicast routing daemon can be active at a time, so it's impossible to run smcroute and, e.g., mrouted at the same time.

Because smcroute modifies the kernel routing table it needs to run with full superuser rights. Which also means that the same applies to client operations, to be able to communicate with the daemon.

WARNING

By using multiple output interfaces (traffic multiplication), using the input interface also as output interface (direct loop) or constructing some other forms of indirect loops you can easily flood your networks!

OPTIONS

-d: Start the smcroute daemon. Will attempt to set up multicast routes and group joins from the file /etc/smcroute.conf, or any alternate config file specified by -f FILE is also provided.
-n: Run daemon in foreground, do not detach from controlling terminal
-N: By default smcroute enables virtual interfaces (VIF) on all multicast capable interfaces in the system. This option inverts that behavior, all VIFs are disabled by default. On systems with many interfaces, where multicast routing only makes use of a few, this can be very useful. The config file setting phyint IFNAME enable enables only the interfaces needed.
-f FILE: Alternate configuration file, default /etc/smcroute.conf
-e CMD: Specify external script or command to be called when smcroute has loaded/reloaded all static multicast routes from the configuration file, or when a source-less (ANY) rule has been installed.
-L LEVEL: Set log level: none, err, info, notice, debug. Default is notice.
-s: Let daemon log to syslog, default unless running in foreground.
-v: Display program version and exit.
-h: Print a help message and exit.
-k: Stop (kill) running daemon.

The -e CMD option is useful if you want to trigger other processes to start when smcroute 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 smcroute also sets two environment variables: source, and group. Beware that these environment variables are unconditionally overwritten by smcroute and can thus not be used to pass information to the script from outside of smcroute.

COMMANDS

The following are commands that can only be passed to an already running daemon.

-a INIFNAME SOURCE GROUP OUTIFNAME [OUTIFNAME ...]: Add a multicast route to the kernel routing cache so that multicast packets received on the network interface INIFNAME originating from the IP address SOURCE and sent to the multicast group addess 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.
-r IFNAME SOURCE GROUP: Remove a kernel multicast route.
-j IFNAME GROUP: Join a multicast group on a given interface.
-l IFNAME GROUP: Leave a multicast group on a given interface.

Multicast routes can be added with the -a command and removed with the -r command.

To be able to add/remove routes or join/leave multicast groups using these commands the smcroute daemon must run. You can also write all rules in the configuration file and send SIGHUP to the daemon.

A multicast route is defined by an input interface IFNAME, the sender's unicast IP address SOURCE, 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 IPv4 addresses or IPv6 addresses. If IPv4 addresses are specified then SMCRoute will operate on the IPv4 multicast routes. If IPv6 addresses are specified then SMCRoute will operate on the IPv6 multicast routes.

The output interfaces are not needed when removing routes using the -r 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, dynamic multicast routing is in nearly all cases the preferred solution. The reason for this is their ability to translate Layer-3 signalling to Layer-2 and vice versa (IGMP or MLD).

smcroute 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 smcroute on. However, this feature of smcroute is only intended as a temporary workaround, and only 20 groups can be joined this way (kernel limit). For bigger installations it is strongly recommended that the user instead fix the root cause to why the designated multicast router does to receive all the required multicast groups on its input interface(s).

To emulate a multicast client using smcroute you use the -j and -l 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.

With this command smcroute allows the integration of nodes that need static multicast routing into dynamic multicast routing domains.

CONFIGURATION FILE

From version 1.98.0 smcroute 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.

#
# 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 mgroup should really not be needed!  It is only available
#       to aid a user in figuring out problems in multicast forwarding.
#       Only 20 mgroup lines can be configured, this is a HARD kernel
#       maximum.  If you need more, you probably need to find another
#       way of forwarding multicast to your router.
#
# Similarily supported is setting mroutes. Removing mroutes is not
# supported, remove/comment out the mroute or send a remove command.
#
# Syntax:
#   phyint IFNAME <enable|disable> [ttl-threshold <1-255>]
#   mgroup from IFNAME group MCGROUP
#   mroute from IFNAME [source ADDRESS] group MCGROUP 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

# 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 group 225.1.2.3 source 192.168.1.42 to eth1 eth2

# 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

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.

From 1.99.0 the sender's IP address is actually optional for IPv4 multicast routes. If omitted it defaults to 0.0.0.0 (INADDR_ANY) and will cause smcroute to dynamically at runtime add new routes, matching the group and inbound interface, to the kernel. This feauture is experimental.

Following the standard UNIX tradition the file format support comments 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, the daemon by default lists 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

smcroute responds to the following signals:

HUP: Restarts smcroute. The configuration file is re-read every time this signal is received.
INT: Terminates execution gracefully.
TERM: The same as INT.

For convenience in sending signals, smcroute 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 added/restored when starting, or restarting the daemon on SIGHUP.
/var/run/smcroute.pid: Pidfile (re)created by smcroute daemon when it has started up and is ready to receive commands.
/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.
/var/run/smcroute: IPC socket created by the smcroute daemon.
/proc/net/igmp: Holds active IGMP joins.
/proc/net/igmp6: Holds active MLD joins.

BUGS

The English wording of this man page.

AUTHORS

Originally written by Carsten Schill <carsten@cschill.de>. Support for IPv6 was added by Todd Hayton <todd.hayton@gmail.com>. Support for FreeBSD was added by Micha Lenk <micha@debian.org>.

SMCRoute 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.