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IPv6/multicast setup on switches
![[ca]](/s/countries/ca.gif) Shadow Hawkins on Wednesday, 21 May 2014 23:45:43
Having just been hit by an IP6 multicast flood, I'm now wondering why I should even see a multicast flood.
In IPv4, if I join a multicast group, my OS sends an IGMP packet up the switch tree towards the router, turning on switches to forward the data packets. So if a few people on the network are watching multicast streamed video, it does not flood all segments, but only those where people are watching.
IPv6 uses MLD with ICMP6, not IGMP.
So why am I seeing packets I'm not subscribed to ? Is it that our switches are too old and don't support IPv6 multicast filtering, or that this filtering model is missing from the protocol ?
For that matter, why should any devices be sensitive to a multicast flood if the packets are supposed to be filtered my MAC address at the hardware level ?
IPv6/multicast setup on switches
Unless your switch does multicast snooping (which typically is separate for IPv4 and IPv6, hence it might support IPv4 snooping but not IPv6) it does not understand much about the IGMP packets.
Hence, when that happens your switch will just use the generic Ethernet Multicast rules to forward the packets, which typically means: send it to all ports.
IPv6 uses MLD with ICMP6, not IGMP.
IPv4 uses IGMPv2, while IPv6 is IGMPv3, both reside kinda inside ICMP.
It might thus be that your switch just does not support snooping it.
As for the actual flooding, some switches have rate limiters for that. But that also depends on the model of the switch again.
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on Thursday, 22 May 2014 08:28:10
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