IP
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... host implementation
of the Internet Protocol (IP) to support multicasting. It is
proposed as a standard for IP multicasting ...
... IP) to support multicasting. It is
proposed as a standard for IP multicasting in the Internet. This
specification is a major revision of RFC-988(-> 1112std5 | 1054(-> 1112std5)) ...
... host group", a set of zero or more hosts identified by a single IP
destination address. A multicast ...
... reliability as regular unicast IP datagrams, i.e., the datagram is
not guaranteed to arrive intact at all members of the destination ...
... group has a
well-known, administratively assigned IP address. It is the address,
not the membership of the group ...
... group, that is permanent; at any time a
permanent group may have any number of members, even zero. Those IP
multicast addresses that are not reserved for permanent groups are
...
... as long as they have members.
Internetwork forwarding of IP multicast datagrams is handled by
"multicast routers ...
... destination host group. If the datagram has an IP
time-to-live greater than 1, the multicast router ...
...
This memo specifies the extensions required of a host IP
implementation to support IP multicasting, where a "host ...
... There are three levels of conformance to this specification:
Level 0: no support for IP multicasting.
There is, at this time, no requirement ...
...
There is, at this time, no requirement that all IP implementations
support IP multicasting. Level 0 hosts ...
... requirement that all IP implementations
support IP multicasting. Level 0 hosts will, in general, be
unaffected by multicast ...
... datagrams can easily be identified by the presence of a class D IP
address in their destination address field; they should be quietly
discarded by hosts ...
... destination address field; they should be quietly
discarded by hosts that do not support IP multicasting. Class D
addresses ...
... Level 1: support for sending but not receiving multicast IP
datagrams.
Level 1 allows a host ...
... join any host groups. An IP implementation may be upgraded
from level 0 to level 1 very easily and with little new code. Only
sections 4, 5, and 6 of this memo are applicable to level 1
...
... implementations.
Level 2: full support for IP multicasting.
Level 2 allows a host ...
... Internet Group Management Protocol (IGMP) and extension of the IP and
local network service interfaces ...
... Host groups are identified by class D IP addresses, i.e., those with
"1110" as their high-order four bits. Class ...
... "1110" as their high-order four bits. Class E IP addresses, i.e.,
those with "1111" as their high-order four bits, are reserved for
...
... group, and 224.0.0.1 is assigned
to the permanent group of all IP hosts. This is used to address all
...
... network. There is no
multicast address (or any other IP address) for all hosts on the
total Internet ...
... The multicast extensions to a host IP implementation are specified in
terms of the layered model illustrated below. In this model, ICMP
...
... hosts) IGMP are considered to be implemented within
the IP module, and the mapping of IP addresses to local network
...
... IGMP are considered to be implemented within
the IP module, and the mapping of IP addresses to local network
addresses ...
... |__________________________________________________________|
--------------------- IP Service Interface -----------------------
__________________________________________________________
...
... __________________________________________________________
| | |
| Local | IP-to-local address mapping |
| Network ...
... To support level 1 multicasting, a host IP implementation must
support the transmission of multicast IP datagrams ...
... IP implementation must
support the transmission of multicast IP datagrams. To support level
2 IP multicasting, a host ...
... multicast IP datagrams. To support level
2 IP multicasting, a host must also support the reception of
multicast ...
... 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 ...
... in a separate section, below. For each service, extensions are
specified for the IP service interface, the IP module, the local
...
... SENDING MULTICAST IP DATAGRAMS ...
... Extensions to the IP Service Interface ...
... Multicast IP datagrams are sent using the same "Send IP" operation
used to send unicast IP datagrams ...
... IP" operation
used to send unicast IP datagrams; an upper-layer protocol module
merely specifies an IP ...
... IP datagrams; an upper-layer protocol module
merely specifies an IP host group address, rather than an individual
...
... host group address, rather than an individual
IP address, as the destination. However, a number of extensions may
be necessary or desirable.
...
... service interface should provide a way for the upper-layer
protocol to specify the IP time-to-live of an outgoing multicast
...
... 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 ...
... Extensions to the IP Module ...
...
To support the sending of multicast IP datagrams, the IP module must
be extended to recognize IP ...
... To support the sending of multicast IP datagrams, the IP module must
be extended to recognize IP host ...
... IP datagrams, the IP module must
be extended to recognize IP host group addresses when routing ...
... interface is required to
support the sending of multicast IP datagrams. The IP module merely
specifies an IP ...
... host group destination, rather than an individual IP
destination, when it invokes the existing "Send Local" operation.
...
... 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 ...
... Ethernet
packets. All that is needed to support the sending of multicast IP
datagrams is a procedure for mapping IP host group addresses to
...
... multicast address
by placing the low-order 23-bits of the IP address into the low-order
23 bits of the Ethernet ...
... multicast address 01-00-5E-00-00-00 (hex).
Because there are 28 significant bits in an IP host group address,
...
... way as Ethernet for the purpose of sending multicast IP datagrams.
For a network that supports broadcast ...
... be mapped to the well-known local address of an IP multicast router;
a router on such a network ...
... Extensions to the IP Service Interface ...
...
Incoming multicast IP datagrams are received by upper-layer protocol
modules using the same "Receive IP ...
... IP datagrams are received by upper-layer protocol
modules using the same "Receive IP" operation as normal, unicast
datagrams ...
... upper-layer protocol is based
on the protocol field in the IP header, regardless of the destination
IP address. However, before any datagrams destined to a particular
...
... on the protocol field in the IP header, regardless of the destination
IP address. However, before any datagrams destined to a particular
group ...
... to join that group. Thus, the IP service interface must be extended
to provide two new operations:
...
... Extensions to the IP Module ...
...
To support the reception of multicast IP datagrams, the IP module
must be extended to maintain a list of host ...
... To support the reception of multicast IP datagrams, the IP module
must be extended to maintain a list of host group ...
...
An incoming datagram is not rejected for having an IP time-to-live of
1 (i.e., the time-to-live ...
... datagrams that are not being forwarded). An incoming
datagram is not rejected for having an IP host group address in its
...
... Problem, Source Quench, or Redirect) is never generated in response
to a datagram destined to an IP host group.
...
... filter (see section 7.3).
The IP module must also be extended to implement the IGMP protocol,
specified in Appendix I. IGMP ...
... Incoming local network multicast packets are delivered to the IP
module using the same "Receive Local" operation as local network
...
... network
unicast packets. To allow the IP module to tell the local network
module which multicast packets ...
... JoinLocalGroup operation requests the local network module to accept
and deliver up subsequently arriving packets destined to the given IP
host group address ...
... group address. The LeaveLocalGroup operation requests the local
network module to stop delivering up packets destined to the given IP
host group address ...
... group address. The local network module is expected to map the
IP host group addresses to local network ...
...
To support the reception of multicast IP datagrams, an Ethernet
module must be able to receive packets addressed to the Ethernet ...
... multicast addresses that correspond to the host's IP host group
addresses. It is highly desirable to take advantage of any address ...
... filtering within the software of the Ethernet module. This is not
mandatory, however, because the IP module performs its own filtering
based on IP ...
... Ethernet for the purpose of receiving multicast IP
datagrams. For pure broadcast networks, such as the Experimental ...
... Ethernet, all incoming broadcast packets can be accepted and passed
to the IP module for IP-level filtering. On point-to-point ...
... broadcast packets can be accepted and passed
to the IP module for IP-level filtering. On point-to-point or
...
... Like ICMP, IGMP is a integral part of IP. It is required to be
implemented by all hosts conforming to level 2 of the IP multicasting ...
... IP. It is required to be
implemented by all hosts conforming to level 2 of the IP multicasting
specification. IGMP messages are encapsulated ...
... specification. IGMP messages are encapsulated in IP datagrams, with
an IP protocol number of 2. All IGMP messages ...
... encapsulated in IP datagrams, with
an IP protocol number of 2. All IGMP messages of concern to hosts
...
... Host Membership Report message, the group address field
holds the IP host group address of the group ...
... host group address being reported, and with an IP
time-to-live of 1, so that other members of the same group ...
... timer expires first.
Note that the multicast routers receive all IP multicast
datagrams, and therefore need not be addressed explicitly.
...
... pseudo-random number generator to compute the
reporting delays, one of the host's own individual IP address should
be used as part of the seed for the generator, to reduce the chance
of multiple hosts ...
... state transition
diagram below. A host may be in one of three possible states, with
respect to any single IP host group on any single network interface ...
...
This appendix is not part of the IP multicasting specification, but
provides background discussion of several issues related to IP ...
... IP multicasting specification, but
provides background discussion of several issues related to IP host
group addresses ...
... hosts may be
considered a generalization of the binding of IP unicast addresses.
An IP unicast ...
... IP unicast addresses.
An IP unicast address is statically bound to a single local network
interface on a single IP network ...
... IP unicast address is statically bound to a single local network
interface on a single IP network. An IP host group address ...
... address is statically bound to a single local network
interface on a single IP network. An IP host group address is
...
... 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 ...
... host group address is NOT
bound to a set of IP unicast addresses. The multicast routers do not
...
... group having local members, rather than a list of the members'
individual IP or Ethernet addresses.
...
... destination address field of multicast IP datagrams. However, the
fact that group addresses are location-independent (they are not
...
... as the destination address field of datagrams. For example, a mobile
IP host might have a host group address ...
... group actually contains more than
one host. For instance, the IP datagram reassembly algorithm relies
on every host ...
... view of these hazards, this memo specifies the use of host group
addresses only in the IP destination address field. However, it is
recommended that datagrams ...
... This memo does not specify how transient group address are allocated.
It is anticipated that different portions of the IP transient host
group address ...
... group" addresses which are
then algorithmically mapped to a subset of the IP transient host
group addresses ...
... are mapped to Ethernet multicast addresses. A portion of the IP
group address space may be set aside for random allocation by
applications that can tolerate occasional collisions with other
...
... host group are intended for the
recipient. Misdelivery must be detected at a level above IP, using
higher-level identifiers or authentication ...
...
The IP multicast extensions specified in this memo are significantly
different from those specified in RFC-988(-> 1112std5 | 1054(-> 1112std5)). Most of the changes are
...
... gateway architecture of the Internet, and it allows the IP
multicast services (in the same way as the IP unicast services ...
... Internet, and it allows the IP
multicast services (in the same way as the IP unicast services) to be
used among hosts ...
... on the network. Thus, current single-network IP broadcast
applications may be migrated to the use of IP multicast ...
... IP broadcast
applications may be migrated to the use of IP multicast before
multicast routers are widely available. The following changes are a
...
... end-to-end encryption or by imposing restrictions on the
flow of IP multicast datagrams into and out of particular
administrative domains ...
... is joined. This gives the sender another degree of scope
control, beyond the IP time-to-live.
...
... LeaveLocalGroup to emphasize their semantic similarity to the
JoinHostGroup and LeaveHostGroup operations at the IP service
interface.
...