datagram
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... destination address. A multicast datagram is delivered to all
members of its destination host group ...
... reliability as regular unicast IP datagrams, i.e., the datagram is
not guaranteed to arrive intact at all members of the destination ...
... reliability as regular unicast IP datagrams, i.e., the datagram is
not guaranteed to arrive intact at all members of the destination
...
...
Internetwork forwarding of IP multicast datagrams is handled by
"multicast routers" which may be co-resident with, or separate from,
...
... IP datagrams to level 0 hosts. Such
datagrams can easily be identified by the presence of a class D IP
address in their destination address field ...
... IP implementation must
support the transmission of multicast IP datagrams. To provide level
2 multicasting, a host ...
... host must also support the reception of multicast
IP datagrams. Each of these two new services is described in a
separate section, below. For each service ...
... SENDING MULTICAST IP DATAGRAMS ...
... IP" operation
used to send unicast IP datagrams; an upper-layer protocol module
merely specifies an IP ...
... time-to-live of an outgoing multicast
datagram, if such a capability does not already exist. If the
upper-layer protocol chooses not to specify a time-to-live ...
... time-to-live, it should
default to 1 for all multicast IP datagrams, so that an explicit
choice is required to multicast beyond a single network ...
... host
is itself a member of a group to which a datagram is being sent, the
service interface should provide a way for the upper-layer ...
... upper-layer protocol
to inhibit local delivery of the datagram; by default, a copy of the
datagram is looped back. This is a performance ...
... delivery of the datagram; by default, a copy of the
datagram is looped back. This is a performance optimization for
upper-layer ...
...
To support the sending of multicast IP datagrams, the IP module must
be extended to recognize IP ...
... group addresses when routing
outgoing datagrams. Most IP implementations include the following
logic:
...
... group on
the outgoing interface, a copy of the outgoing datagram must be
looped-back for local delivery, unless inhibited by the sender ...
...
The IP source address of the outgoing datagram must be one of the
individual addresses corresponding to the outgoing interface ...
... interface is required to
support the sending of multicast IP datagrams. The IP module merely
specifies an IP ...
... destination field of Ethernet
packets. All that is needed to support the sending of multicast IP
datagrams is a procedure for mapping IP host group addresses ...
... way as Ethernet for the purpose of sending multicast IP datagrams.
For a network that supports broadcast ...
...
Incoming multicast IP datagrams are received by upper-layer protocol
modules using the same "Receive IP ...
... IP" operation as normal, unicast
datagrams. Selection of a destination upper-layer protocol is based
...
... protocol field in the IP header, regardless of the destination
IP address. However, before any datagrams destined to a particular
group can be received, an upper-layer ...
... interface,
in which case duplicate multicast datagrams may be received. It is
also permissible for more than one upper-layer protocol to request
...
...
To support the reception of multicast IP datagrams, the IP module
must be extended to maintain a list of host ...
... group memberships
associated with each network interface. An incoming datagram
destined to one of those groups is processed exactly the same way as
...
... destined to one of those groups is processed exactly the same way as
datagrams destined to one of the host's individual addresses.
...
... entry. On hosts with more than one network interface, if a datagram
arrives via one interface, destined for a group ...
... host
belongs only on a different interface, the datagram is quietly
discarded. (These cases should occur only as a result of inadequate
multicast address ...
... 1 (i.e., the time-to-live should not automatically be decremented on
arriving datagrams that are not being forwarded). An incoming
datagram with an IP ...
... arriving datagrams that are not being forwarded). An incoming
datagram with an IP host group address ...
... Destination Unreachable,
Time Exceeded, Parameter Problem, Source Quench, or Redirect) is
never generated in response to a datagram destined to an IP host
...
...
To support the reception of multicast IP datagrams, an Ethernet
module must be able to receive packets addressed to the Ethernet ...
... Ethernet for the purpose of receiving multicast IP
datagrams. For pure broadcast networks, such as the Experimental ...
... specification. IGMP messages are encapsulated in IP datagrams, with
an IP protocol number of 2. All IGMP messages ...
... multicast routers receive all IP multicast
datagrams, and therefore need not be addressed explicitly.
Further note that the routers need not know which hosts ...
... group address will reach only the intended hosts, or that datagrams
received as a member of a transient host group ...