address
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... hosts identified by a single IP
destination address. A multicast datagram is delivered to all
...
... group has a
well-known, administratively assigned IP address. It is the address,
not the membership of the group ...
... well-known, administratively assigned IP address. It is the address,
not the membership of the 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
available for dynamic assignment ...
... 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 ...
... 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 that do not support IP multicasting ...
... IP multicasting. Class D
addresses are described in section 4 of this memo.
Level 1: support for sending but not receiving ...
... HOST GROUP ADDRESSES ...
... 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
...
... In Internet standard "dotted decimal" notation, host group addresses
range from 224.0.0.0 to 239.255.255.255. The address ...
... group addresses
range from 224.0.0.0 to 239.255.255.255. The address 224.0.0.0 is
guaranteed not to be assigned to any group, and 224.0.0.1 is assigned
...
... hosts on the directly connected network. There is no
multicast address (or any other IP address) for all hosts on the
...
... network. There is no
multicast address (or any other IP address) for all hosts on the
total Internet ...
... IGMP are considered to be implemented within
the IP module, and the mapping of IP addresses to local network
addresses ...
... IP addresses to local network
addresses is considered to be the responsibility of local network
modules. This model is for expository purposes only, and should not
...
... merely specifies an IP host group address, rather than an individual
IP address, as the destination ...
... host group address, rather than an individual
IP address, as the destination. However, a number of extensions may
be necessary or desirable.
...
...
A host group address should not be placed in the source address field
or anywhere in a source routing ...
... A host group address should not be placed in the source address field
or anywhere in a source routing option of an outgoing IP datagram ...
... Ethernet directly supports the sending of local multicast packets
by allowing multicast addresses in the 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 to
Ethernet multicast addresses ...
... host group address is mapped to an Ethernet multicast address
by placing the low-order 23-bits of the IP address ...
... multicast address
by placing the low-order 23-bits of the IP address into the low-order
23 bits of the Ethernet ...
... 23 bits of the Ethernet multicast address 01-00-5E-00-00-00 (hex).
Because there are 28 significant bits in an IP ...
... group address,
more than one host group address may map to the same Ethernet
multicast address ...
... group addresses may be mapped to a
single local broadcast address (at the cost of increased overhead on
all local hosts ...
... group addresses might
be mapped to the well-known local address of an IP multicast router;
a router ...
... on the protocol field in the IP header, regardless of the destination
IP address. However, before any datagrams destined to a particular
group ...
... host group identified by "group-address" on the given network
interface. The LeaveGroup operation requests that this host give up
...
... Both operations should return immediately (i.e., they are non-
blocking operations), indicating success or failure. Either
operation may fail due to an invalid group address or interface
identifier. JoinHostGroup may fail due to lack of local resources.
LeaveHostGroup may fail because the host ...
... interface, the datagram is quietly discarded.
(These cases should occur only as a result of inadequate multicast
address filtering in a local network module.)
...
... datagram is not rejected for having an IP host group address in its
source address field or anywhere in a source routing ...
... host group address in its
source address field or anywhere in a source routing option. An ICMP
error message (Destination ...
... join the "all-hosts" group (address 224.0.0.1) on each network
interface at initialization time and must remain a member for as long
...
... time-to-live. Thus, the all-
hosts address may not be used as an internet-wide broadcast address ...
... address may not be used as an internet-wide broadcast address.
For the purpose of IGMP, membership in the all-hosts ...
... enough that overhead is negligible, and (3) the all-hosts address may
serve other routing-oriented purposes, such as advertising the
...
... routing-oriented purposes, such as advertising the
presence of gateways or resolving local addresses.)
...
... address" is an IP host group address. The
JoinLocalGroup operation requests the local network module to accept
...
... IP
host group address. The LeaveLocalGroup operation requests the local
network module to stop delivering up packets destined to the given IP ...
... network module is
free to ignore LeaveLocalGroup requests, and may deliver up packets
destined to more addresses than just those specified in
JoinLocalGroup requests, if it is unable to filter incoming packets ...
... module must be able to receive packets addressed to the Ethernet
multicast addresses that correspond to the host's IP host ...
... host's IP host group
addresses. It is highly desirable to take advantage of any address
filtering ...
... IP host group
addresses. It is highly desirable to take advantage of any address
filtering capabilities that the Ethernet ...
... Unfortunately, many current Ethernet interfaces have a small limit on
the number of addresses that the hardware can be configured to
recognize. Nevertheless, an implementation must be capable of
...
...
listening on an arbitrary number of Ethernet multicast addresses,
which may mean "opening up" the address filter ...
... Ethernet multicast addresses,
which may mean "opening up" the address filter to accept all
multicast packets ...
... filter to accept all
multicast packets during those periods when the number of addresses
exceeds the limit of the filter.
...
...
For interfaces with inadequate hardware address filtering, it may be
desirable (for performance ...
... desirable (for performance reasons) to perform Ethernet address
filtering within the software of the Ethernet ...
... Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
... In a Host Membership Query message, the group address field
is zeroed when sent, ignored when received.
...
... destination address equal to the
host group address being reported, and with an IP
time-to-live ...
... 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 ...
... IP destination field and its IGMP group address
field, to ensure that the host's own Report is not cancelled by an
...
... destination field and its IGMP group address field. A Report
applies only to the membership in the group identified by the
...
... APPENDIX II. HOST GROUP ADDRESS ISSUES ...
... Group Address Binding ...
... addresses.
An IP unicast address is statically bound to a single local network
interface on a single IP network. An IP ...
... IP network. An IP host 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 ...
... 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 Addresses as Logical Addresses ...
... Group Addresses as Logical Addresses ...
...
Host group addresses have been defined specifically for use in the
destination address field of multicast ...
... Host group addresses have been defined specifically for use in the
destination address field of multicast IP datagrams. However, the
...
... multicast IP datagrams. However, the
fact that group addresses are location-independent (they are not
statically bound to a single network interface) suggests possible
...
... statically bound to a single network interface) suggests possible
uses as more general "logical addresses", both in the source as well
as the destination address field of datagrams ...
... uses as more general "logical addresses", both in the source as well
as the destination address field of datagrams. For example, a mobile
IP host ...
... mobile
IP host might have a host group address as its only identity, used as
the source of datagrams ...
... network. Other hosts
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 ...
...
Host group addresses cannot, however, be used to solve all problems
of internetwork logical addressing, such as delivery ...
... network interface of a multi-homed host.
Furthermore, there are hazards in using group addresses in the source
address field of datagrams when the group ...
... multi-homed host.
Furthermore, there are hazards in using group addresses in the source
address field of datagrams when the group actually contains more than
...
... algorithm relies
on every host using a different source address. Also, errors in a
datagram sent with a group ...
... datagram sent with a group source address may result in error reports
being returned to all members of the group, not just the sender ...
...
view of these hazards, this memo specifies the use of host group
addresses only in the IP destination address field. However, it is
...
... host group
addresses only in the IP destination address field. However, it is
recommended that datagrams with a group ...
... recommended that datagrams with a group source address, or a group
address as part of a source routing option, be accepted without
...
... datagrams with a group source address, or a group
address as part of a source routing option, be accepted without
complaint, thereby allowing other implementations to experiment with
...
... Allocation of Transient Host Group Addresses ...
...
This memo does not specify how transient group address are allocated.
It is anticipated that different portions of the IP transient host ...
... IP transient host
group address space will be allocated using different techniques.
For example, there may be a number of servers that can be contacted
to acquire a new transient group address ...
... group address space will be allocated using different techniques.
For example, there may be a number of servers that can be contacted
to acquire a new transient group address. Some higher-level
protocols (such as VMTP, specified in RFC-1045exp ...
... group" or "entity group" addresses which are
then algorithmically mapped to a subset of the IP transient host ...
... group addresses, similarly to the way that IP host group addresses
are mapped to Ethernet multicast addresses ...
... group addresses
are mapped to Ethernet multicast addresses. A portion of the IP
group address space may be set aside for random allocation by
...
... 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
multicast ...
... applications that can tolerate occasional collisions with other
multicast users, perhaps generating new addresses until a suitably
"quiet" one is found.
...
... datagrams sent to any host
group address will reach only the intended hosts, or that datagrams
...
... tokens. Information
transmitted to a host group address should be encrypted or governed
by administrative routing ...