network
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... IP multicast datagram as a
local network multicast which reaches all immediately-neighboring
members of the destination host ...
... time-to-live greater than 1, the multicast router(s) attached to the
local network take responsibility for forwarding it towards all other
networks that have members of the destination ...
... local network take responsibility for forwarding it towards all other
networks that have members of the destination group. On those other
...
... destination group. On those other
member networks that are reachable within the IP time-to-live, an
...
... hosts and will be specified in
separate documents. This memo also does not specify how local
network multicasting is accomplished for all types of network,
...
... network multicasting is accomplished for all types of network,
although it does specify the required service interface to an
...
... although it does specify the required service interface to an
arbitrary local network and gives an Ethernet specification as an
example. Specifications for other types of network ...
... network and gives an Ethernet specification as an
example. Specifications for other types of network will be the
subject of future memos.
...
... unaffected by multicast activity. The only exception arises on some
types of local network, where the presence of level 1 or 2 hosts may
cause misdelivery of multicast ...
... IGMP) and extension of the IP and
local network service interfaces within the host. All of the
...
... multicast hosts on the directly connected network. There is no
multicast address (or any other IP address ...
... the IP module, and the mapping of IP addresses to local network
addresses is considered to be the responsibility of local network ...
... network
addresses is considered to be the responsibility of local network
modules. This model is for expository purposes only, and should not
be construed as constraining an actual implementation.
...
... |__________________________________________________________|
---------------- Local Network Service Interface -----------------
__________________________________________________________
...
... IP-to-local address mapping |
| Network | (e.g., ARP) |
| Modules |_____________________________|
...
... interface, the IP module, the local
network service interface, and an Ethernet local network ...
... network service interface, and an Ethernet local network module.
Extensions to local network modules other than Ethernet ...
... Ethernet local network module.
Extensions to local network modules other than Ethernet are mentioned
briefly, but are not specified in detail.
...
... IP datagrams, so that an explicit
choice is required to multicast beyond a single network.
Second, for hosts ...
...
Second, for hosts that may be attached to more than one network, the
service interface should provide a way for the upper-layer ...
... service interface should provide a way for the upper-layer protocol
to identify which network interface is be used for the multicast
transmission. Only one interface ...
... transmission; multicast routers are responsible for forwarding to any
other networks, if necessary. If the upper-layer protocol chooses
not to identify an outgoing interface ...
... Extensions to the Local Network Service Interface ...
...
No change to the local network service interface is required to
support the sending of multicast ...
...
Other networks that directly support multicasting, such as rings or
buses conforming to the IEEE 802.2 ...
... multicast IP datagrams.
For a network that supports broadcast but not multicast, such as the
...
... multicasts should be transmitted
exactly like unicasts. For a store-and-forward network like the
ARPANET or a public X.25 ...
... IP multicast router;
a router on such a network would take responsibility for completing
multicast delivery ...
... group identified by "group-address" on the given network
interface. The LeaveGroup operation requests that this host give up
its membership in the host ...
... group-address" on the
given network interface. The interface argument may be omitted on
hosts ...
... interface argument may be omitted on
hosts that may be attached to only one network. For hosts that may
be attached to more than one network ...
... network. For hosts that may
be attached to more than one network, the upper-layer protocol may
choose to leave the interface ...
... host group memberships
associated with each network interface. An incoming datagram
destined to one of those groups ...
... any error report. On hosts
attached to more than one network, if a datagram arrives via one
network interface ...
... network, if a datagram arrives via one
network interface, destined for a group to which the host belongs
...
... (These cases should occur only as a result of inadequate multicast
address filtering in a local network module.)
An incoming datagram ...
... group on a given interface, the local network module for that
interface is notified, so that it may update ...
... host group memberships present on a
particular local network. To support IGMP, every level 2 host must
...
... hosts" group (address 224.0.0.1) on each network
interface at initialization time and must remain a member for as long
as the host ...
... special case by the multicast routers and are never forwarded beyond
a single network, regardless of their time-to-live. Thus, the all-
hosts ...
... Extensions to the Local Network Service Interface ...
... multicast packets are delivered to the IP
module using the same "Receive Local" operation as local network
unicast packets. To allow the IP ...
... unicast packets. To allow the IP module to tell the local network
module which multicast packets to accept, the local network service ...
... network
module which multicast packets to accept, the local network service
interface is extended to provide two new operations:
...
... host group address. The
JoinLocalGroup operation requests the local network module to accept
and deliver up subsequently arriving packets destined to the given IP
...
... host group address. The LeaveLocalGroup operation requests the local
network module to stop delivering up packets destined to the given IP
host ...
... update its multicast reception filter. Any local network module is
free to ignore LeaveLocalGroup requests, and may deliver up packets
destined to more addresses ...
... adequately.
The local network module must not deliver up any multicast packets
that were transmitted from that module; loopback ...
... multicast networks, such as IEEE 802.2 networks, can be handled
the same way as Ethernet for the purpose of receiving ...
... filtering. On point-to-point or
store-and-forward networks, multicast IP datagrams will arrive as
...
... multicast IP datagrams will arrive as
local network unicasts, so no change to the local network module
...
... host groups have members on their
attached local networks. Queries are addressed to the all-hosts
...
... host group to which they
belong on the network interface from which the Query was received.
In order to avoid an "implosion" of concurrent Reports and to reduce
...
... timer for each of its
group memberships on the network interface of the incoming
Query. Each timer ...
... time-to-live of 1, so that other members of the same group on
the same network can overhear the Report. If a host hears a
Report for a group ...
... host hears a
Report for a group to which it belongs on that network, the
host stops its own timer ...
... Report will be generated for each group present on the
network, by the member host whose delay timer expires first.
...
... host belongs to a
group on a particular network.
There are two exceptions to the behavior described above. First, if
...
... Queries periodically to refresh their
knowledge of memberships present on a particular network. If no
Reports are received for a particular group after some number of
...
... multicasts for that
group onto the local network. Queries are normally sent infrequently
(no more than once a minute) so as to keep the IGMP ...
... Query, in case it is
the first member of that group on the network. To cover the
possibility of the initial Report being lost or damaged, it is
recommended that it be repeated once or twice after short delays. (A
...
... interface. This is the initial state for all
memberships on all network interfaces; it requires no storage
in the host.
...
... An IP unicast address is statically bound to a single local network
interface on a single IP network. An IP host ...
... IP unicast address is statically bound to a single local network
interface on a single IP network. An IP host group address ...
... host group address is
dynamically bound to a set of local network interfaces on a set of IP
networks.
...
... group address is
dynamically bound to a set of local network interfaces on a set of IP
networks.
It is important to understand that an IP ...
... fact that group addresses are location-independent (they are not
statically bound to a single network interface) suggests possible
uses as more general "logical addresses", both in the source as well
...
... datagrams it sends. Whenever the mobile host moved
from one network to another, it would join its own group on the new
...
... join its own group on the new
network and depart from the group on the old network. Other hosts ...
... network and depart from the group on the old network. Other hosts
communicating with the mobile one would deal only with the group
address ...
... communicating with the mobile one would deal only with the group
address and would be unaware of, and unaffected by, the changing
network location of the mobile host.
...
... addressing, such as delivery to the "nearest"
or the "least loaded" network interface of a multi-homed host.
Furthermore, there are hazards in using group addresses ...
... services) to be
used among hosts on a single network when no router is up or present
on the network ...
... network when no router is up or present
on the network. Thus, current single-network IP broadcast ...
... - The handling of IP time-to-live, and of multiple network
interfaces, has been more precisely specified.
...
...
- The AcceptAddress and RejectAddress operations at the local
network service interface have been renamed JoinLocalGroup and
LeaveLocalGroup to emphasize their semantic ...