IGMP snooping is a multicast protocol running in layer 2 devices. It enables multicast traffic mode to overcome the issue of network congestion and data security incidents by unicast mode. Today it is widely configured on IGMP-enabled devices to guarantee device and network reliability. This article will dive into IGMP snoop. Hoping you will have a clear picture of what IGMP snooping is, how it works, and how to configure it on QSFPTEK IGMP snooping switches.
What Is IGMP Snooping?
GMP (Internet Group Management Protocol) Snooping is a network protocol for switches to listen to the Internet Group Management Protocol traffic. Devices enabling IGMP Snooping can identify which hosts in the network are interested in joining the multicast group. Then, when the switch sends IGMP multicast traffic once, all receivers that have solicited will receive the traffic simultaneously. The other hosts that are not interested will filter out the traffic and discard the package, then bandwidth is reserved in these links.
What is Multicast in Networking?
Network multicast mode is a forwarding mode that delivers multicast traffic from a single source but is received by multiple destination receivers.
Compared to unicast mode, multicast is more efficient since the traffic only needs to be forwarded once. Also, multicast is superior to broadcast for requested information is only sent to the right receivers. Generally speaking, if you have multicast traffic on your network and devices supporting IGMP, then enabling IGMP snooping is recommended.
What is IGMP Snooping Switch?
Network switches that support using the IGMP protocol to listen to the Internet Group Management Protocol traffic between hosts and routers are IGMP snooping switches. IGMP snooping empowers switches to learn which links require which IP multicast traffic and forward respective data to destinated links.
What is the Main Purpose of IGMP Snooping?
IGMP snooping mainly solves the issue of traffic floods, data security leakage, and inefficient data communication.
Prevent Traffic Floods: IGMP switches only forward IPv4 packets to those ports that belong to the multicast group instead of sending them to all ports in the VLAN. This prevents the hosts from processing unnecessary packets that they are not solicited. Bandwidth on those links is conserved and thus improving bandwidth utilization and making the network faster and more efficient.
Enhance Data Security: Only selective users will receive the multicast packets, which prevent unauthorized access to private data. The network that doesn’t enable IGMP Snooping might face a denial-of-service (DoS) attack at any time.
How IGMP Snooping Works?
IGMP snooping can listen to the IGMP packets between the multicast-enabled hosts and routers. If an IGMP snooping switch receives a message from a host for joining the multicast group, the switch will add the host to the multicast group membership table. If the switch receives a message from a host for detaching the multicast group, the switch will remove the host from the multicast membership table.
When the switch receives multicast packets, it can quickly identify the interesting receivers by checking the multicast forwarding table and then selectively forward the message to those interfaces connected to the multicast groups.
Understanding IGMP Message Types
IGMP snooping query is the message sent from the switch or router (also known as Querier) to ask for a specific response from each of the hosts in the multicast group. For example, the query may be: “Is there any host listening to a specific multicast group?” or “Is there any host listening to a specific group multicast traffic from a specific multicast source?”
Membership Report (Join Group):
Join Group is the message sent by the host to ask for permission from the IGMP Querier for joining a specific multicast group.
Leave Group is the message sent by the host to inform the IGMP snooping Querier to leave a specific multicast group.
Top Considerations on IGMP Snooping Configurations
Enable IGMP snooping is essential for improving network efficiency and preventing traffic floods. To properly configure IGMP snooping, you should keep the following considerations in mind.
Having a picture of network topology in mind helps to locate the multicast sources and receivers. Checking whether switches and other devices in the topology support IGMP snooping is also essential when deciding where to get started with the configuration.
IGMP Querier is responsible for sending IGMP snooping queries and maintaining the multicast membership table. Properly configuring IGMP Querier can ensure multicast traffic forwarding in the right way.
IGMP Proxy as an IGMP feature has extended the capability of IGMP snooping. It enables the layer 2 switches (with layer 3 routing features) as a proxy to forward IGMP passages across different VLAN or hosts and multicast routers in subnets. This solves the limitation of IGMP snooping working only in a specific VLAN and con not forwarding packets between different VLANs.
You should configure IGMP snooping based on each VLAN, which requires targeted VLAN configuration to realize multicast traffic isolation and control.
IGMPv1, IGMPv2, and IGMPv3 are the three progressive versions of IGMP. Mind learning the features of each version since different versions require different IGMP configurations for your networks.
This feature allows IGMP to filter multicast links based on the VLAN interface level. Simply put, it is to configure an IP multicast configuration profile and relate it with each port of switches. Then ports are designated whether to receive or discard the multicast traffic. It is a secure mechanism for selectively forwarding multicast packets
Aging Timeout Value
IGMP timeout value specifies how long the switch will wait to receive an IGMP query from the multicast router until removing the multicast group from the multicast cache table. Deciding to conserve the default timeout value (260 seconds) or change it to an optimal value depends on your requirement.
How to Configure IGMP-Snooping on QSFPTEK Enterprise Switches?
The following is the IGMP snooping configuration guide for QSFPTEK S5300 series layer 2 switches. This configuration manual applies to the following models: S5300-8T2S, S5300-8P2S, S5300-16S8TS4X, S5300-24T4S, S5300-24T4X, S5300-24P4TS, S5300-24P4X, S5300-48T4X, S5300-48P6X.
Click L2 Config -> IGMP Snooping in the navigation bar, and enter the
IGMP-Snooping Configuration page.
On this page, you can set whether to make a switch to forward unknown multicasts,
whether to enable IGMP snooping, and whether to configure the switch as the querier
IGMP-Snooping VLAN List
In the navigation bar, click L2 Config -> IGMP Snooping -> IGMP Snooping VLAN
list in the navigation bar, and enter IGMP-Snooping VLAN page.
If you click New, IGMP-snooping VLAN configuration can be done. Through Web up to 8
physical ports can be set on each IGMP snooping VLAN. If you click Cancel, a selected
IGMP-Snooping VLAN can be deleted; if you click Edit, you can modify the member port, running
status, and immediate leave of IGMP-Snooping VLAN.
When creating a new IGMP-Snooping VLAN, VLAN ID can be modified; when modifying IGMP-Snooping
VLAN, VLAN ID cannot be modified.
You can add or delete the routing port by buttons “>>” or “<<”.
Static Multicast Address
Click L2 Config -> IGMP Snooping > Static Multicast Address List in the navigation
bar, and enter the static multicast address configuration page.
This page displays the static multicast group in the current network according to
IGMP-Snooping statistics and the port set to which each member belongs to.
Click “Refresh” to refresh the contents in the list.
Click the Multicast List Info option on the top of the page and the Multicast List Info page appears.
On this page, the multicat groups, which are existent in the current network and are in
the statistics of IGMP snooping, as well as port sets to which members in each group
belong are displayed.
Click “Refresh” to refresh the contents in the list.
All QSFPTEK brand managed switches support IGMP protocol, for specific switch model configuration, please check the following switch configuration and commands manuals: