> in RFC4294 in section 4.6 MLDv2 support is a SHOULD for all "nodes that > need to join multicast groups"
In reading this, the current wording is not particularly clear. The first "if" means that the SHOULD really ought to be a MUST (IMO). I.e., if a node has an application that runs multicast, it MUST run MLD. Otherwise, things won't work properly. That said, one needs to run MLD just to support Neighbor Discovery properly (see 7.2.1 of RFC 4861). So, it would appear that running MLD really is a MUST in practice. Well, almost. One needs to run MLD on link technologies that require the use of ND (and multicast) _and_ that may be bridged, i.e, LANs. But I can imagine some link types where there won't be bridging, and more importantly, IP multicast won't be supported and Address Resolution is done in a link-specific way. See section 5.2 of the node-req-bis document for more explanation. So I think a MUST for MLD is too strong, but _just_ barely. :-) So, I wonder whether the better text for this section would be something like: Nodes that need to join multicast groups MUST support MLD. MLD is needed by any node that is expected to receive and process multicast traffic. Note that Neighbor Discovery (as used on most link types -- see Section 5.2) depends on multicast and requires that nodes join Solicited Node multicast addresses. Nodes SHOULD implement MLDv2 [RFC3810]. However, if the node has applications that only need support for Any-Source Multicast, the node MAY implement MLDv1 [RFC2710] instead. If the node has applications that need support for Source-Specific Multicast [RFC3569], [RFC4607], the node MUST support MLDv2 [RFC3810]. In all cases, nodes are strongly encouraged to implement MLDv2 rather than MLDv1, as the presence of a single MLDv1 participant on a link requires that all other nodes on the link operate in version 1 compatability mode. If MLDv1 is implemented, the rules in the Source Address Selection for the Multicast Listener Discovery (MLD) Protocol [RFC3590] MUST be followed. Thomas -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
