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Applies to RadioOS: v4.5

  • Packages required: multicast
  • Incompatible with: routing-test (v3)


Internet Group Management Protocol (IGMP) proxy can be used to implement multicast routing. It is forwarding IGMP frames and commonly is used when there is no need for more advanced protocol like PIM.

IGMP proxy features:

  • The simplest way how to do multicast routing;
  • Can be used in topologies where PIM-SM is not suitable for some reason;
  • Takes slightly less resources than PIM-SM;
  • Ease of configuration.

On the other hand, IGMP proxy is not well suited for complicated multicast routing setups. Compared to PIM based solutions, IGMP proxy does not support more than one upstream interface and routing loops are not detected or avoided.

CableFree RadioOS IGMP proxy supports IGMP version 2 (RFC 2236).


To forward all multicast data coming from ether1 interface to all other interfaces, where subscribers are connected:

[admin@CableFree] /routing igmp-proxy> interface add interface=ether1 upstream=yes
[admin@CableFree] /routing igmp-proxy> interface add interface=all
[admin@CableFree] /routing igmp-proxy> interface print
Flags: X - disabled, I - inactive, D - dynamic, U - upstream
 #    INTERFACE                                                             THRESHOLD
 0  U ether1                                                                1
 1    all                                                                   1
 2 D  ether2                                                                1
 3 D  ether3                                                                1

You may also need to configure alternative-subnets on upstream interface - in case if the multicast sender address is in an IP subnet that is not directly reachable from from the local router.

[admin@CableFree] /routing igmp-proxy> interface set [find upstream=yes] \

/routing igmp-proxy

General configuration.

  • query-interval (time, 00:00:01 - 01:00:00) : how often to send out IGMP Query messages over upstream interface
  • query-response-interval (time, 00:00:01 - 01:00:00) : how long to wait for responses to an IGMP Query message
  • quick-leave (yes|no) : specifies action on IGMP Leave message. If quick-leave is on, then an IGMP Leave message is sent upstream as soon as a leave is received from the first client on the downstream interface. Use set to yes only in case there is only one subscriber behind the proxy.

Note: use quick leave only if there is one subscriber behind the proxy

/routing igmp-proxy interface

Used to configure what interfaces will participate as IGMP proxy interfaces on router. If an interface is not configured as IGMP proxy interface, then all IGMP traffic received on it will be ignored.

  • alternative-subnets (list of IP prefixes) : by default, only packets from directly attached subnets are accepted. This parameter can be used to specify a list of alternative valid packet source subnets, both for data or IGMP packets. Has effect only on upstream interface. Should be used when the source of multicast data often is in a different IP network.
  • interface (interface name) : RadioOS interface
  • threshold (integer) : minimal TTL; packets received with a lower TTL value are ignored
  • upstream (yes|no) : interface is called "upstream" if it's in the direction of the root of the multicast tree. An IGMP forwarding router must have exactly one upstream interface configured. The upstream interface is used to sent out IGMP membership requests.

/routing igmp-proxy mfc

Multicast forwarding cache (MFC) status.

  • group (IP address) : IGMP group address
  • source (IP address) : multicast data originator address
  • incoming-interface (interface name) : packet stream is coming in router through this interface
  • outgoing-interface (interface name) : packet stream is going out of router through this interface

Static multicast forwarding cache (MFC) entries

Since RadioOS 4.5 MFC is enabled to add static multicast forwarding rules. If a static rule is added, all dynamic rules for that group will be ignored.


These rules will take effect only if IGMP-proxy interfaces are configured (upstream and downstram interfaces should be set) or these rules wont be active.

  • downstream-interfaces (list of interfaces) : received stream will be sent out to listed interfaces only.
  • group (multicast group address) : multicast stream group address this rule applies should be set
  • source (IP address) : IP address we are receiving stream from should be set
  • upstream-interface (interface) : interface that is receiving stream data should be set



Will forward stream unconditionally if it comes in from ether1 with set source and will be sent out to ether2, clients that will try to get stream on interface ether3 will not receive that stream.

/routing igmp-proxy interface add comment="" disabled=no interface=ether1 threshold=1 upstream=yes
/routing igmp-proxy interface add comment="" disabled=no interface=ether2 threshold=1
/routing igmp-proxy interface add comment="" disabled=no interface=ether3 threshold=1
/routing igmp-proxy mfc add source= upstream-interface=ether1 \
downstream-interface=ether2 group= disabled=no

MFC static entry group will not be sent at all

/routing igmp-proxy mfc add source= upstream-interface=ether1 \
group= disabled=no


RFC 4605 IGMP/MLD - Based Multicast Forwarding