05-07-2018 03:50 AM - edited 03-05-2019 10:24 AM
The NDP protocol makes use of the solicited-node multicast address.
A host joins its own solicited-node multicast address group both localy (netsh int ipv6 show joins) and on the layer2 domain (a wireshark trace shows that a host configured with a new IPv6 address sends a MLD message for its solicited-node multicast address).
Yet, a Cisco layer2 switch (S0) with IPv6 MLD snooping enabled, placed in between three hosts PC1,PC2,Server1 and an IPv6 PIMv2 router shows:
. no display of solicited-node multicast groups
. a recorded link-local multicast group (Multicast DNS, FF02::FB)
Doing some experiments shows that:
. IPv6 MLD snooping is functionning OK with regular IPv6 Multicast traffic, with the traffic correctly switched relevant to the multicast joined clients (ie not-flooded)
. solicited-node multicast is not snooped, but flooded instead
So is IPv6 MLD snooping performed by switches over solicited-node multicast address? Or is it flooded by design ?
Thanks for any input :-)
05-07-2018 05:10 AM
According to RFC4451, all link scope (ff02::/16) multicast address should support MLD, except for FF02::1. In principle, MLD should apply to all these multicast groups.
https://www.ietf.org/rfc/rfc4541.txt
RFC4451, section
In IPv6, the data forwarding rules are more straight forward because MLD is mandated for addresses with scope 2 (link-scope) or greater. The only exception is the address FF02::1 which is the all hosts link-scope address for which MLD messages are never sent. Packets with the all hosts link-scope address should be forwarded on all ports.
Regards,
11-23-2021 03:21 PM
As each host creates at least one multicast sollicited node address, you would end up with enormous MLD tables.
Read this nanog archive https://archive.nanog.org/sites/default/files/tues.general.wheeler.neighbor.12.pdf
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