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IGMP (Internet Group Management Protocol) and MLD (Multicast Listener Discovery) snooping allow the bridge to listen to IGMP/MLD communication and make forwarding decisions for multicast traffic based on the received information. By default, bridges are flooding multicast traffic to all bridge ports just like broadcast traffic, which might not always be the best scenario (e.g. for multicast video traffic or SDVoE applications). The IGMP/MLD snooping tries to solve the problem by forwarding the multicast traffic only to ports where clients are subscribed to, see an IGMP/MLD network concept below. RouterOS bridge is able to process IGMP v1/v2/v3 and MLD v1/v2 packets. The implemented bridge IGMP/MLD snooping is based on RFC4541, and IGMP/MLD protocols are specified on RFC1112 (IGMPv1) RFC2236 (IGMPv2), RFC3376 (IGMPv3), RFC2710 (MLDv1), RFC3810 (MLDv2).

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Property

Description

igmp-snooping (yes | no; Default: no)Enables IGMP and MLD snooping.
igmp-version (2 | 3; Default: 2)Selects the IGMP version in which IGMP membership queries will be generated when the bridge interface is acting as an IGMP querier. This property only has an effect when igmp-snooping and multicast-querier is set to yes.
last-member-interval (time; Default: 1s)

When the last client on the bridge port unsubscribes to a multicast group and the bridge is acting as an active querier, the bridge will send group-specific IGMP/MLD query, to make sure that no other client is still subscribed. The setting changes the response time for these queries. In case no membership reports are received in a certain time period (last-member-interval * last-member-query-count), the multicast group is removed from the multicast database (MDB).

If the bridge port is configured with fast-leave, the multicast group is removed right away without sending any queries.

This property only has an effect when igmp-snooping and multicast-querier is set to yes.

last-member-query-count (integer: 0..4294967295; Default: 2)How many times should last-member-interval pass until the IGMP/MLD snooping bridge stops forwarding a certain multicast stream. This property only has an effect when igmp-snooping and multicast-querier is set to yes.
membership-interval (time; Default: 4m20s)The amount of time after an entry in the Multicast Database (MDB) is removed if no IGMP/MLD membership reports are received on a bridge port. This property only has an effect when igmp-snooping is set to yes.
mld-version (1 | 2; Default: 1)Selects the MLD version in which MLD membership queries will be generated, when the bridge interface is acting as an MLD querier. This property only has an effect when the bridge has an active IPv6 address, igmp-snooping and multicast-querier is set to yes.
multicast-querier (yes | no; Default: no)

Multicast querier generates periodic IGMP/MLD general membership queries to which all IGMP/MLD capable devices respond with an IGMP/MLD membership report, usually a PIM (multicast) router or IGMP proxy generates these queries.

By using this property you can make an IGMP/MLD snooping enabled bridge to generate IGMP/MLD general membership queries. This property should be used whenever there is no active querier (PIM router or IGMP proxy) in a Layer2 network. Without a multicast querier in a Layer2 network, the Multicast Database (MDB) is not being updated, the learned entries will timeout and IGMP/MLD snooping will not function properly.

Only untagged IGMP/MLD general membership queries are generated, IGMP queries are sent with IPv4 0.0.0.0 source address, MLD queries are sent with IPv6 link-local address of the bridge interface. The bridge will not send queries if an external IGMP/MLD querier is detected (see the monitoring values igmp-querier and mld-querier).

This property only has an effect when igmp-snooping is set to yes.

multicast-router (disabled | permanent | temporary-query; Default: temporary-query)A multicast router port is a port where a multicast router or querier is connected. On this port, unregistered multicast streams and IGMP/MLD membership reports will be sent. This setting changes the state of the multicast router for a bridge interface itself. This property can be used to send IGMP/MLD membership reports and multicast traffic to the bridge interface for further multicast routing or proxying. This property only has an effect when igmp-snooping is set to yes.
  • disabled - disabled multicast router state on the bridge interface. Unregistered multicast streams and IGMP/MLD membership reports are not sent to the bridge interface regardless of what is configured on the bridge interface.
  • permanent - enabled multicast router state on the bridge interface. Unregistered multicast streams and IGMP/MLD membership reports are sent to the bridge interface itself regardless of what is configured on the bridge interface.
  • temporary-query - automatically detect multicast router state on the bridge interface using IGMP/MLD queries.
querier-interval (time; Default: 4m15s)Changes the timeout period for detected querier and multicast-router ports. This property only has an effect when igmp-snooping is set to yes.
query-interval (time; Default: 2m5s)Changes the interval on how often IGMP/MLD general membership queries are sent out when the bridge interface is acting as an IGMP/MLD querier. The interval takes place when the last startup query is sent. This property only has an effect when igmp-snooping and multicast-querier is set to yes.
query-response-interval (time; Default: 10s)The setting changes the response time for general IGMP/MLD queries when the bridge is active acting as an IGMP/MLD querier. This property only has an effect when igmp-snooping and multicast-querier is set to yes.
startup-query-count (integer: 0..4294967295; Default: 2)Specifies how many times general IGMP/MLD queries must be sent when bridge interface is enabled or active querier timeouts. This property only has an effect when igmp-snooping and multicast-querier is set to yes.
startup-query-interval (time; Default: 31s250ms)Specifies the interval between startup general IGMP/MLD queries. This property only has an effect when igmp-snooping and multicast-querier is set to yes.

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Property

Description

fast-leave (yes | no; Default: no)Enables IGMP/MLD fast leave feature on the bridge port. The bridge will stop forwarding multicast traffic to a bridge port when an IGMP/MLD leave message is received. This property only has an effect when igmp-snooping is set to yes.
multicast-router (disabled | permanent | temporary-query; Default: temporary-query)A multicast router port is a port where a multicast router or querier is connected. On this port, unregistered multicast streams and IGMP/MLD membership reports will be sent. This setting changes the state of the multicast router for bridge ports. This property can be used to send IGMP/MLD membership reports and multicast streams to certain bridge ports for further multicast routing or proxying. This property only has an effect when igmp-snooping is set to yes.
  • disabled - disabled multicast router state on the bridge port. Unregistered multicast streams and IGMP/MLD membership reports are not sent to the bridge port regardless of what is connected to it.
  • permanent - enabled multicast router state on the bridge port. Unregistered multicast and IGMP/MLD membership reports are sent to the bridge port regardless of what is connected to it.
  • temporary-query - automatically detect multicast router state on the bridge port using IGMP/MLD queries.
unknown-multicast-flood (yes | no; Default: yes)

Changes the multicast flood option on bridge port, only controls the egress traffic. When enabled, the bridge allows flooding multicast packets to the specified bridge port, but when disabled, the bridge restricts multicast traffic from being flooded to the specified bridge port. The setting affects all multicast traffic, this includes non-IP, IPv4, IPv6 and the link-local multicast ranges (e.g. 224.0.0.0/24 and ff02::1).

Note that when igmp-snooping is enabled and IGMP/MLD querier is detected, the bridge will automatically restrict unknown IP multicast from being flooded, so the setting is not mandatory for IGMP/MLD snooping setups.

When using this setting together with igmp-snooping, the only multicast traffic that is allowed on the bridge port is the known multicast from the MDB table. 

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Below are described the most common configuration examples. Some examples are using a bridge with VLAN filtering, so make sure to understand the filtering principles first - bridge VLAN filteringbridge VLAN table.

Basic IGMP snooping configuration

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First, create a bridge on both devices and add needed interfaces as bridge ports. To change untagged VLAN for a bridge port, use the pvid setting. The Bridge1 will be acting as an IGMP querier. Below are configuration commands for the Bridge1:

Code Block
languageros
/interface bridge
add igmp-snooping=yes multicast-querier=yes name=bridge1
/interface bridge port
add bridge=bridge1 interface=ether2 pvid=10
add bridge=bridge1 interface=ether3 pvid=10
add bridge=bridge1 interface=ether4 pvid=10
add bridge=bridge1 interface=ether5 pvid=20
add bridge=bridge1 interface=sfp-sfpplus1 pvid=10

And for the Bridge2:

Code Block
languageros
/interface bridge
add igmp-snooping=yes name=bridge1
/interface bridge port
add bridge=bridge1 interface=ether3 pvid=10
add bridge=bridge1 interface=ether4 pvid=10
add bridge=bridge1 interface=ether5 pvid=20
add bridge=bridge1 interface=sfp-sfpplus1

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 pvid=10


Note

Bridge IGMP querier implementation can only send untagged IGMP queries. In case tagged IGMP queries should be sent or IGMP queries should be generated in multiple VLANs, it is possible to install a multicast package, add a VLAN interface and configure a PIM interface on VLAN. The PIM interface can be used as an IGMP querier.

Make sure to configure management access for your devices for devices. It is essential when configuring a bridge with VLAN filtering. In this example, a VLAN 99 interface with an IP address is added to the bridge. This VLAN will be allowed on the tagged sfp-sfpplus1 port. Below are configuration commands for the Bridge1:

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Code Block
languageros
/interface vlan
add interface=bridge1 name=MGMT vlan-id=99
/ip address
add address=192.168.99.2/24 interface=MGMT network=192.168.99.0
/interface bridge vlan
add bridge=bridge1 tagged=bridge1,sfp-sfpplus1 vlan-ids=99

To change port untagged VLAN, use pvid setting. Below are configuration commands for the Bridge1: 

Code Block
languageros
/interface bridge port
set [find interface=ether2] pvid=10
set [find interface=ether3] pvid=10
set [find interface=ether4] pvid=10
set [find interface=ether5] pvid=20
set [find interface=sfp-sfpplus1] pvid=10

And for the Bridge2:

Code Block
languageros
/interface bridge port
set [find interface=ether3] pvid=10
set [find interface=ether4] pvid=10
set [find interface=ether5] pvid=20
set [find interface=sfp-sfpplus1] pvid=10
Note
Bridge IGMP querier implementation can only send untagged IGMP queries. In case tagged IGMP queries should be sent or IGMP queries should be generated in multiple VLANs, it is possible to install a multicast package, add a VLAN interface and configure a PIM interface on VLAN. The PIM interface can be used as an IGMP querier.
add address=192.168.99.2/24 interface=MGMT network=192.168.99.0
/interface bridge vlan
add bridge=bridge1 tagged=bridge1,sfp-sfpplus1 vlan-ids=99

Add bridge VLAN entries and specify tagged and untagged ports. The VLAN 99 entry was already created when configuring management access, only VLAN 10 and VLAN 20 should be added now. Below are configuration commands for the Bridge1:

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At this point, VLANs and IGMP snooping are configured and devices should be able to communicate through the ports. However, it is recommended to go even a step further and apply some additional filtering options. Enable port ingress-filtering and frame-types on bridge ports. Below are configuration commands for the Bridge1:

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