host
Click on the red underlined text to get to the source
...
This memo specifies the extensions required of a host implementation
of the Internet Protocol (IP ...
... IP multicasting is the transmission of an IP datagram to a "host
group", a set of zero or more hosts ...
... multicast datagram is delivered to all
members of its destination host group with the same "best-efforts"
reliability ...
... and leave groups at any time. There is no restriction on the
location or number of members in a host group. A host may be a
...
... location or number of members in a host group. A host may be a
member of more than one group at a time. A host ...
... host may be a
member of more than one group at a time. A host need not be a member
of a group to send datagrams ...
... network multicast which reaches all immediately-neighboring
members of the destination host group. If the datagram has an IP ...
...
This memo specifies the extensions required of a host IP
implementation to support IP multicasting ...
... host" is any
internet host or gateway other than those acting as multicast
routers. The algorithms ...
... algorithms and protocols used within and between
multicast routers are transparent to hosts and will be specified in
separate documents. This memo also does not specify how local
network ...
... IP implementations
support IP multicasting. Level 0 hosts will, in general, be
unaffected by multicast activity. The only exception arises on some
...
... 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 IP datagrams ...
... cause misdelivery of multicast IP datagrams to level 0 hosts. Such
datagrams can easily be identified by the presence of a class ...
... IP
address in their destination address field; they should be quietly
discarded by hosts that do not support IP multicasting. Class D
...
... services,
such as resource location or status reporting, but it does not allow
a host to join any host groups ...
... groups, as well as send
IP datagrams to host groups. It requires implementation of the
Internet Group Management Protocol ...
... local network service interfaces within the host. All of the
following sections of this memo are applicable to level 2
implementations.
...
... HOST GROUP ADDRESSES ...
... used to address all multicast hosts on the directly connected
network. There is no multicast address ...
... multicast address (or any other IP address) for
all hosts on the total Internet. The addresses of other well-known ...
... Appendix II contains some background discussion of several issues
related to host group addresses.
...
...
The multicast extensions to a host IP implementation are specified in
terms of the layered model illustrated below. In this model, ICMP ...
... terms of the layered model illustrated below. In this model, ICMP
and (for level 2 hosts) IGMP are considered to be implemented within
the IP ...
...
To provide level 1 multicasting, a host IP implementation must
support the transmission of multicast ...
... IP datagrams. To provide level
2 multicasting, a host must also support the reception of multicast
IP datagrams ...
... upper-layer protocol module
merely specifies an IP host group address, rather than an individual
IP address ...
...
Third (level 2 implementations only), for the case in which the host
is itself a member of a group to which a datagram ...
... upper-layer protocols that restrict the membership of a group to one
process per host (such as a routing protocol), or that handle
loopback ...
... Experimental Ethernet, all IP host group addresses may be mapped to a
single local broadcast ...
... address (at the cost of increased overhead on
all local hosts). For a point-to-point link joining two hosts (or a
...
... all local hosts). For a point-to-point link joining two hosts (or a
host and a multicast router ...
... point-to-point link joining two hosts (or a
host and a multicast router), multicasts should be transmitted
...
... The JoinHostGroup operation requests that this host become a member
of the host group identified by "group-address ...
... group-address" on the given network
interface. The LeaveGroup operation requests that this host give up
its membership in the host group ...
... network
interface. The LeaveGroup operation requests that this host give up
its membership in the host group identified by "group-address ...
... network interface. The interface argument may be omitted on
hosts that support only one interface. For hosts that may be
...
... hosts that support only one interface. For hosts that may be
attached to more than one network, the upper-layer ...
... group address or interface
identifier. JoinHostGroup may fail due to lack of local resources.
LeaveHostGroup may fail because the host does not belong to the given
group on the given interface ...
... IP datagrams, the IP module
must be extended to maintain a list of host group memberships
associated with each network interface ...
... groups is processed exactly the same way as
datagrams destined to one of the host's individual addresses.
...
... Incoming datagrams destined to groups to which the host does not
belong are discarded without generating any error report or log
...
... belong are discarded without generating any error report or log
entry. On hosts with more than one network interface, if a datagram
...
... arrives via one interface, destined for a group to which the host
belongs only on a different interface, the datagram ...
...
The list of host group memberships is updated in response to
JoinHostGroup and LeaveHostGroup requests from upper-layer ...
... specified in Appendix I. IGMP is used to keep neighboring multicast
routers informed of the host group memberships present on a
particular local network ...
... network
interface at initialization time and must remain a member for as long
as the host is active.
...
...
(Datagrams addressed to the all-hosts group are recognized as a
special case by the multicast routers ...
... network, regardless of their time-to-live. Thus, the all-
hosts address may not be used as an internet-wide broadcast ...
... address.
For the purpose of IGMP, membership in the all-hosts group is really
necessary only while the host ...
... hosts group is really
necessary only while the host belongs to at least one other group.
However, it is specified that the host ...
... host belongs to at least one other group.
However, it is specified that the host shall remain a member of the
all-hosts group ...
... However, it is specified that the host shall remain a member of the
all-hosts group at all times because (1) it is simpler, (2) the
frequency of reception of unnecessary IGMP ...
... queries should be low
enough that overhead is negligible, and (3) the all-hosts address may
serve other routing ...
... group-address" is an IP host group address. The
JoinLocalGroup operation requests the local network ...
... and deliver up subsequently arriving packets destined to the given IP
host group address. The LeaveLocalGroup operation requests the local
network ...
... network module to stop delivering up packets destined to the given IP
host group address. The local network module is expected to map the
...
... multicast addresses that correspond to the host's IP host group
addresses. It is highly desirable to take advantage of any address
...
... hardware interface may have,
so that the host receives only those packets that are destined to it.
...
... IP hosts to
report their host group memberships to any immediately-neighboring
multicast routers ...
... multicast routers. IGMP is an asymmetric protocol and is specified
here from the point of view of a host, rather than a multicast
router. (IGMP may also be used, symmetrically or asymmetrically,
...
... IGMP is a integral part of IP. It is required to be
implemented by all hosts conforming to level 2 of the IP multicasting
specification. IGMP messages ...
... an IP protocol number of 2. All IGMP messages of concern to hosts
have the following format:
...
... is zeroed when sent, ignored when received.
In a Host Membership Report message, the group address field
holds the IP ...
... Query messages (hereinafter
called Queries) to discover which host groups have members on their
attached local networks ...
... Hosts respond to a Query by generating Host Membership Reports
(hereinafter called Reports), reporting each host group ...
... Query by generating Host Membership Reports
(hereinafter called Reports), reporting each host group to which they
belong on the network interface ...
... value between zero and D seconds. When a timer expires, a
Report is generated for the corresponding host group. Thus,
Reports are spread out over a D second interval instead of
...
... group on
the same network can overhear the Report. If a host hears a
Report for a group to which it belongs on that network ...
... group to which it belongs on that network, the
host stops its own timer for that group and does not generate
...
... group present on the
network, by the member host whose delay timer expires first.
Note that the multicast routers ...
... datagrams, and therefore need not be addressed explicitly.
Further note that the routers need not know which hosts
belong to a group, only that at least one host ...
... hosts
belong to a group, only that at least one host belongs to a
group on a particular network ...
... rather allowed to continue running with its current value. Second, a
report delay timer is never set for a host's membership in the all-
hosts group ...
... timer is never set for a host's membership in the all-
hosts group (224.0.0.1), and that membership is never reported.
...
...
If a host uses a pseudo-random number generator to compute the
reporting delays, one of the host ...
... host uses a 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
...
... IP address should
be used as part of the seed for the generator, to reduce the chance
of multiple hosts generating the same sequence of delays.
...
... IGMP group address
field, to ensure that the host's own Report is not cancelled by an
erroneous received Report. A host should quietly discard any IGMP ...
... field, to ensure that the host's own Report is not cancelled by an
erroneous received Report. A host should quietly discard any IGMP
message of type other than Host ...
... host should quietly discard any IGMP
message of type other than Host Membership Query or Host Membership
...
... (no more than once a minute) so as to keep the IGMP overhead on hosts
and networks very low. However, when a multicast router ...
... IGMP behavior is more formally specified by the state transition
diagram below. A host may be in one of three possible states, with
respect to any single IP host ...
... host may be in one of three possible states, with
respect to any single IP host group on any single network interface:
...
... memberships on all network interfaces; it requires no storage
in the host.
...
... valid IGMP
Host Membership Report message. To be valid, the Report
message must be at least 8 octets ...
... group (address 224.0.0.1) is handled as a special case.
The host starts in Idle Member state for that group ...
... APPENDIX II. HOST GROUP ADDRESS ISSUES ...
... host group addresses to physical hosts may be
considered a generalization of the binding of IP unicast ...
... network
interface on a single IP network. An IP host group address is
dynamically bound to a set of local network interfaces ...
...
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
need to maintain a list of individual members of each host group.
For example, a multicast router ...
... associate only a single Ethernet multicast address with each host
group having local members, rather than a list of the members'
...
... Allocation of Transient Host Group Addresses ...
... group address are allocated.
It is anticipated that different portions of the IP transient host
group address space will be allocated using different techniques.
...
... addresses which are
then algorithmically mapped to a subset of the IP transient host
group addresses, similarly to the way that IP ...
... In general, a host cannot assume that datagrams sent to any host
group address will reach only the intended hosts ...
... host
group address will reach only the intended hosts, or that datagrams
received as a member of a transient host ...
... hosts, or that datagrams
received as a member of a transient host group are intended for the
recipient. Misdelivery must be detected at a level above IP ...
... authentication tokens. Information
transmitted to a host group address should be encrypted or governed
...