- IGMP snooping
IGMP Snooping is the process of listening to IGMP traffic. IGMP snooping, as implied by the name, is a feature that allows the switch to "listen in" on the IGMP conversation between hosts and
router s by processing the layer 3 IGMP packets sent in amulticast network.When IGMP snooping is enabled in a switch it analyzes all IGMP packets between hosts connected to the switch and multicast routers in the network. When a switch hears an IGMP report from a host for a given multicast group, the switch adds the host's port number to the multicast list for that group. And, when the switch hears an IGMP Leave, it removes the host's port from the table entry.
IGMP snooping can very effectively reduce multicast traffic from streaming and other bandwidth intensive IP applications. While a switch that does not understand multicast will broadcast multicast traffic to all the ports in a broadcast domain (a LAN), a switch using IGMP snooping will only forward multicast traffic to the hosts interested in that traffic. This reduction of multicast traffic reduces the packet processing at the switch (at the cost of needing additional memory to handle the multicast tables) and also reduces the workload at the end hosts since their network cards (or
operating system ) will not have to receive and filter all the multicast traffic generated in the network.See also
* IGMP - Internet Group Management Protocol
* MLD - Multicast Listener Discovery
*Network switch
= RFC reference =* RFC 4541 - Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches. M. Christensen, K. Kimball, F. Solensky. May 2006. (Format: TXT=38555 bytes) (Status: INFORMATIONAL)
* RFC 3376 - Internet Group Management Protocol, Version 3. B. Cain, S. Deering, I. Kouvelas, B. Fenner, A. Thyagarajan. October 2002.(Format: TXT=119726 bytes) (Obsoletes RFC2236) (Updated by RFC4604)(Status: PROPOSED STANDARD)
* Verify the status of the RFCs in RFC index - [http://www.ietf.org/iesg/1rfc_index.txt]
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