IGMP Filter

This topic is to discuss the following lesson:

What would be the utility of this in real life?

Hello Stefanio

There are several reasons why we would want to filter IGMP packets. The most basic and important reason is to allow for a network to function more efficiently. The details follow:

IGMP filtering allows users to configure filters on a switch virtual interface (SVI), a per-port, or a per-port per-VLAN basis to control the propagation of IGMP traffic through the network. By managing the IGMP traffic, IGMP filtering provides the capability to manage IGMP snooping, which in turn controls the forwarding of multicast traffic.

When an IGMP packet is received, IGMP filtering uses the filters configured by the user to determine whether the IGMP packet should be discarded or allowed to be processed by the existing IGMP snooping configuration.

The major purpose of this is to reduce the number of packets that have to be processed by network and end devices and as a result free up their resources and make the network more efficient.

I hope this has been helpful!

Laz

Hello Rene

I have a simple question about this topic. About Router filter, its only when you want to block from this net to another upstream router, cause i can see if source and destination is in the same net (this example) they can forward traffic normaly or in some way router gives this information to switch to not consider this blocked multicast group. Thnkas for your asnwer.

Jose

Hello Jose

The IGMP filter function can be configured on both a router and a switch. When configured on a router, then yes, only multicast traffic between subnets are filtered. If you want to filter within the same subnet, then switches that have IGMP Snooping Filter capability can filter multicast traffic at ports, VLANs or SVIs.

There is no communication between the router and the switch for such configurations. Each device is configured independently.

I hope this has been helpful!

Laz

Lazaros thanks for your answer!

1 Like

According to Official Cert Guide, you can also filter IGMPv1 messages via the filter. How do you do this?

Hello Chris

According to Cisco:

Filtering on the IGMP protocol allows you to configure the minimum version of IGMP hosts allowed on the SVI. For example, you may want to disallow all IGMPv1 hosts (such as, allow a minimum IGMP version of 2) or all IGMPv1 and IGMPv2 hosts (such as, allow a minimum IGMP version of 3). This filtering applies only to membership reports.

To configure filtering on the IGMP protocol, use the following CLI command:

ip igmp snooping minimum-version 2 | 3

This filter is only configurable on a Layer 3 SVI as a default filter for all ports in access mode under that SVI and for the corresponding VLAN on all trunk ports.

This has been taken from this Cisco documentation.

I hope this has been helpful!

Laz

How exactly is this filtering efficient than SSM? Understand later is for v3 only. This implies denial on control plane itself rather than data plane for SSM?

Hi Deep,

With SSM, you can filter specific sources. IGMP filter is still useful to filter the multicast groups themselves, and it works for any IGMP version.

Rene