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Single-source IP Multicast Address Range
Description:
The IP multicast address range 232.X.X.X is to be designated for
single-source multicast applications and protocols. This means that
an IP multicast packet sent by host S to an address E in this range
should be delivered to each host H that has done a source-specific
join to (S,E) as supported in the proposed IGMPv3 and PIM. The
delivery semantics for other cases of IP multicast packets sent to an
address E in this range are undefined. In particular, a router is
free to drop (rather than forward) a packet sent by S to E in this
range if no host has communicated a source-specific join to this
router for (S,E). Multiple sources can use the same address E in this
range with the above semantics and without conflict: packets from each
source Si are delivered only to hosts that joined to (Si,E).
Plan:
1) IANA recharacterizes this address range as single-source multicast
addresses from its current VMTP multicast designation, updating the
assigned number documents accordingly, and citing the above
description for their semantics. No further action is required by
IANA. In particular, no additional address allocation within this
range is required.
2) No transition plan is required because VMTP use of this address
range is compatible with the above single-source semantics, and no
other protocols are assigned for use in this address range.
Moreover, current IP multicast routing protocols provide a superset
of these semantics, so are compatible.
3) Experimental work will proceed with protocols for supporting
single-source multicast and source-specific joins, as in IGMPv3,
leading to protocol proposals for suitable review and consideration
by the IETF. Any higher-level (than IP) protocol may use this
space, within the specified single-source semantics.
[DRC3] David Cheriton, <cheriton@DSG.Stanford.EDU>, October 1998.
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