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How to Configure Cisco SF300/SG300/SG500 Multicast

You can establish group memberships between different users within a network. IGMP is mainly used for multimedia streaming, such as video-chat, between different users (one-to-many users or many-to-many users) in a network

Configuring IGMP Snooping

IGMP Snooping must be enabled on the switch to manage the flow of registered multicast traffic. Once IGMP Snooping is enabled multicast groups will be registered on the switch when receivers request to join multicast groups. Multicast traffic destined for registered multicast groups will then be forwarded only to interfaces on which group-member receivers are attached.

1) Under Multicast > Properties enable the Bridge Multicast Filtering Status setting (disabled by default) and click Apply

Bridge Multicast Filtering
Bridge Multicast Filtering

2) Under Multicast > IPv4 Multicast Configuration > IGMP Snooping enable the IGMP Snooping Status setting (disabled by default) and click Apply

IGMP Snooping VLAN

3) Under Multicast > IPv4 Multicast Configuration > IGMP Snooping select the VLAN you want to enable IGMP Snooping on and click Edit

IGMP Snooping
IGMP Snooping edit

4) In the Edit IGMP Snooping Settings popup window (popups need to be enabled in the browser) enable the IGMP Snooping Status setting and click Apply:

IGMP Snooping Status 

5) Confirm that the IGMP Snooping Operation Status shown for the VLAN under Multicast > IPv4 Multicast Configuration > IGMP Snooping now says “Enabled”:

IGMP Snooping Operation Status

6) Under Multicast > Unregistered Multicast configure all interfaces for Filtering (set to Forwarding by default) and click Apply. This prevents unregistered multicast (i.e., streams from encoded that are not being requested by any decoders) from flooding to any interfaces.

Unregistered Multicast

Configuring IGMP Querier

ach VLAN that manages multicast traffic with IGMP Snooping requires an IGMP Querier. The IGMP Querier periodically queries the VLAN to confirm that receivers want to maintain memberships with multicast groups. If multiple Queriers are enabled on the same VLAN an automatic election process will occur – the Querier with the lowest IP will win and all other Queriers will stop sending queries. The position of the Querier in a multi-switch environment should be carefully considered, especially for a high-bandwidth multicast application, as all multicast traffic always flows towards the Querier. Without a Querier the multicast group memberships on IGMP Snooping switches will timeout after a set period of time (typically 260 seconds) requiring the receivers to then rejoin the multicast group in order to start receiving multicast traffic again.

1) Under Multicast > IPv4 Multicast Configuration > IGMP Snooping confirm that the IGMP Querier Status setting is enabled (enabled by default). If it is disabled, enable it:

IGMP Querier Status

2) Under Multicast > IPv4 Multicast Configuration > IGMP Snooping select the VLAN you want to enable IGMP Querier on and click Edit:

IGMP Table Vlan

3) In the Edit IGMP Snooping Settings popup window enable the IGMP Querier Status setting (disabled by default), confirm that the IGMP Querier Version setting is configured for v2 (v2 is default), and click Apply.

Querier Status

Configuring Non-Querier in Multi-Switch Environment

Any Cisco SG switches in a multi-switch IGMP Snooping environment that are not intended to be the Querier should still be configured to enable IGMP Snooping. In addition it is important that the non-Querier switch knows which interface connects to the Querier so multicast traffic can be forwarded appropriately – all multicast traffic needs to flow towards the Querier via the Multicast Router (mrouter) Port. The Multicast Router Port can be dynamically learned (by listening for Queries) or statically assigned. By default, Cisco SG will forward unregistered multicast traffic to all interfaces and the filtering/forwarding of unregistered multicast traffic is a per-interface setting. If the unregistered multicast filtering setting is applied to an interface which is also the Multicast Router Port the Cisco SG will not forward unregistered traffic to the mrouter port. This behaviour of not forwarding all multicast traffic to the Querier is at odds with the requirements defined in the IGMP standard in that all multicast traffic should always flow towards the Querier so can cause issues if sharing multicast traffic between sources and receivers connected to different switches in a multi-switch environment.

1) Under Multicast > IPv4 Multicast Configuration > IGMP Snooping disable the IGMP Querier Status setting (enabled by default) and click Apply. Disabling this global setting overrides the IGMP Querier Status settings of the individual VLAN’s:

IGMP Snooping disable

2) Under Multicast > Multicast Port confirm that the switch has discovered the Querier on one of the interfaces, listed as Dynamic. Note that it may take some time for this multicast router port to be discovered:

Multicast Router Port

The Multicast Router Port can be statically configured by selecting “Static” however this configuration should only be required recommended if switches from different vendors are used in the same network environment and they are not able to auto-discover the IGMP Querier.

If the Multicast Router Port is not able to be dynamically discovered this could indicate that there is no IGMP Querier configured on the network. In a single-switch environment the IGMP Querier feature must be enabled in order to prevent group-membership timeouts but in a multi-switch environment an IGMP Querier is also required in order for multicast traffic to flow from one IGMP Snooping enabled switch to another.

3) Now that the Multicast Router Port has been configured (either dynamically discovered or statically assigned) under Multicast > Unregistered Multicast configure the same interface to Forwarding. All interfaces that are not Multicast Router Ports should be set to Filtering:

Unregistered Multicast

This is done because the Unregistered Multicast setting on the Cisco SG300/SG500 switches overrides the default behaviour of how switches are supposed to handle the flow of multicast traffic to Multicast Router Ports in that all multicast traffic should always be forwarded to the Multicast Router Port (i.e., towards the Querier).

Configuring Immediate Leave

When a receiver leaves a multicast group the traffic flowing to the interface destined for that group does not stop straight away. IGMP allows time for the Querier to confirm that other receivers, possibly attached to the same interface and joined to the same multicast group, do not want to maintain a connection to the group once a receiver leaves the group before the forwarding of traffic for that group on that interface ceases. For high-bandwidth multicast applications, where the stream size can easily exceed half the available bandwidth, the Immediate Leave feature should be enabled to prevent data saturation on interfaces where a receiver leaves one group and then immediately joins another group. If you are in a multi switch environment, Immediate Leave feature should be disabled on the core switch, this will prevent drop outs of video on downstream switches if two end points are on the same stream. 

1) Under Multicast > IPv4 Multicast Configuration > IGMP Snooping select the VLAN you want to enable IGMP Snooping on and click Edit:

IGMP Snooping

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