Hardware - Layer-3-aware ASIC and IGMP snooping
Switches use what are known as Application Specific Integrated Circuits (ASICs) which are designed to perform specific tasks, unlike general-purpose processors. They are highly efficient in terms of speed and power consumption, making them ideal for resource intensive tasks.
In particular, Layer3-aware ASICs are used in conduction with IGMP snooping. In a Multicast environment, where IGMP is employed, these ASICs can process Layer 3 information, which is essential for IGMP Snooping as IGMP is a Layer 3 protocol. The L3-Aware ASIC can differentiate between IGMP and non-IGMP messages by examining the Layer 3 part of the packet, not just the MAC address.
In IGMP Snooping implementations L3-Aware ASICs perform the following functions:
- IGMP messages (with multicast MAC addresses starting with 0100.5E) are identified and sent to the CPU for processing.
- Non-IGMP multicast traffic is forwarded directly to the appropriate ports based on previous IGMP snooping information, bypassing the CPU.
This approach allows for more efficient handling of multicast traffic, as the ASIC can make intelligent decisions about packet forwarding without involving the CPU for every multicast packet.
Although the term "Layer 3" is often associated with routing, in the context of IGMP snooping, it’s not about routing, but about the ability of the ASIC to identify, understand, and process Layer 3 information.
Although IGMP is used to help switches (inherently Layer 2 devices) decide on which ports multicast traffic should be forwarded, IGMP also includes Layer 3 information such as the multicast group addresses. Indeed, IGMP is considered a Layer 3 protocol, so a switch that supports IGMP Snooping must have an ASIC that can process Layer 3 information.
Links
https://forum.networklessons.com/t/igmp-snooping/1321/106?u=lagapidis