![]() ![]() In order for IGMP, and thus IGMP snooping, to function, a multicast router must exist on the network and generate IGMP queries. This is why RFC4541 on IGMP snooping carries only an informational status this despite actually being referred to in other standards work, such as RFC4903, as normative. This means that there is no clear standards body responsible for this technique. IGMP snooping, although an important technique, overlaps two standards organizations, namely IEEE which standardizes Ethernet switches, and IETF which standardizes IP multicast. ![]() Snooping is therefore especially useful for bandwidth-intensive IP multicast applications such as IPTV. IGMP snooping allows a switch to only forward multicast traffic to the links that have solicited them. IGMP snooping takes place internally on switches and is not a protocol feature. It provides switches with a mechanism to prune multicast traffic from links that do not contain a multicast listener (an IGMP client).Įssentially, IGMP snooping is a layer 2 optimization for the layer 3 IGMP. IGMP snooping is designed to prevent hosts on a local network from receiving traffic for a multicast group they have not explicitly joined. ![]() ![]() When purposefully exploited, this can form the basis of a denial-of-service attack. Multicast can cause unnecessary load on host devices by requiring them to process packets they have not solicited. A switch will, by default, flood multicast traffic to all the ports in a broadcast domain (or the VLAN equivalent). ![]()
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