As per Relevance of the word multicast, we have this rfc below:
Network Working Group D.
Request for Comments: 1768 NSWC-
Category: Experimental March 1995
Host Group Extensions for CLNP
Status of this
This memo defines an Experimental Protocol for the
community. This memo does not specify an Internet standard of
kind. Discussion and suggestions for improvement are requested
Distribution of this memo is unlimited
This memo documents work performed in the TUBA (TCP/UDP over
Addresses) working group of IPng area prior to the July 1994
to utilize SIPP-16 as the basis for IPng. The TUBA group worked
extending the Internet Protocol suite by the use of ISO 8473 (CLNP
and its related routing protocols. This memo describes
extensions to CLNP and its related routing protocols for
multicast use. Publication of this memo does not imply acceptance
any IETF Working Group for the ideas expressed within
This memo provides a specification for multicast extensions to
CLNP protocol similar to those provided to IP by RFC1112.
extensions are intended to provide the mechanisms needed by a
for multicasting in a CLNP based Internet. This memo
addressing extensions to the CLNP addressing structure, extensions
the CLNP protocol and extensions to the ES-IS protocol. An
discusses the differences between IP multicast and the CLNP
approach provided in this memo
The specification provided here was developed by a number
individuals in the IETF TUBA working group as well as the ANSI X3S3.3
and ISO SC6 WG2 committees. Key contributions were made by
Deering, Joel Halpern, Dave Katz and Dave Oran
Marlow [Page 1]
RFC 1768 CLNP Multicasting March 1995
Table of
1. Introduction .......................................... 2
2. Levels of Conformance.................................. 3
3. Group Network Addresses................................ 4
4. Model of a CLNP End System Multicast Implementation.... 8
5. Extensions to the CLNP Protocol........................ 8
6. Extensions to the ES-IS Routeing Protocol ............. 15
7. Security Considerations ............................... 39
Appendix A. Differences with RFC 1112 .................... 40
Appendix B. Issues Under Study ........................... 43
References ................................................ 44
Author's Address .......................................... 45
1.
This memo provides a specification for multicast extensions for
in order to provide a CLNP based Internet the capabilities
for IP by RFC 1112 (Host Extensions for IP Multicasting) [RFC1112].
This memo uses an outline similar to that of RFC 1112.
Paraphrasing RFC 1112, "CLNP multicasting is the transmission of
CLNP datagram to a "host group", a set of zero or more End
identified by a single group Network address (GNA). A
datagram is delivered to all members of its destination host
with the same "best-efforts" reliability as regular unicast
datagrams, i.e., the datagram is not guaranteed to arrive intact
all members of the destination group or in the same order relative
other datagrams
"The membership of a host group is dynamic; that is End Systems
join and leave groups at any time. There is no restrictions on
location or number of members in a host group. An End System may be
member of more than one group at a time. An End System need not be
member of a group to send datagrams to it
"A host group may be permanent or transient. A permanent group has
administratively assigned GNA. It is the address, not the
of the group, that is permanent; at any time a permanent group
have any number of members, even zero
"Internetwork forwarding of CLNP multicast datagrams is handled
"multicast capable" Intermediate Systems which may be co-
with unicast capable Intermediate Systems
The multicast extensions to the CLNP addressing structure
group Network addresses which identify host groups. The
extensions to CLNP provides a means for identifying a CLNP packet
Marlow [Page 2]
RFC 1768 CLNP Multicasting March 1995
provides scope control mechanisms for CLNP multicast packets.
multicast extensions to the ES-IS protocol provide the
needed for a host to exchange control information with
capable routers. These extensions to the ES-IS protocol provide
a host to "announce" which multicast packets are of interest and
a multicast capable router to dynamically "map" group
addresses to subnetwork addresses
This memo specifies the extensions required by an End System to
use of CLNP multicast. In addition the requirements placed
multicast capable Intermediate Systems to exchange information
multicast capable End Systems is specified. No specifications
provided related to the information exchanges between
Systems to support multicast route selection or multicast
Data Unit (PDU) forwarding. A discussion of multicast route
and PDU forwarding has been written by Steve Deering [Deering91].
Note that for these multicast extensions to work there must exist
uninterrupted path of multicast capable routers between the
Systems comprising a host group (such paths may utilize
(i.e., unicast CLNP encapsulated paths between multicast capable
routers)). In order to support multicast route selection
forwarding for a CLNP based internet additional specifications
needed. Specifications of this type could come in the form of
protocols, extensions to the current CLNP based routing protocols
use of a technique out of the IETF's Inter-Domain Multicast
(IDMR) group. The IDMR group is currently investigating
protocols for routers which utilize a router's unicast
protocols, this approach may extend directly to CLNP routers
While many of the techniques and assumptions of IP multicasting (
discussed in RFC 1112) are used in CLNP multicasting, there
number of differences. Appendix A describes the differences
CLNP multicasting and IP multicasting. This memo describes
brought in directly from projects within ISO to incorporate
transmission capabilities into CLNP [MULT-AMDS].
2. Levels of
There are three levels of conformance for End Systems to
specification
Level 0: no support for CLNP multicasting
There is no requirement for a CLNP End System (or
System) to support CLNP multicasting. Level 0 hosts should
unaffected by the presence of multicast activity. The
addresses used in support of multicast transfers, the GNA, should
be enabled by a non-multicast capable End System and the
Marlow [Page 3]
RFC 1768 CLNP Multicasting March 1995
themselves are marked differently than unicast PDUs and thus
be quietly discarded
Level 1: support for sending but not receiving CLNP multicast PDUs
An End System originating multicast PDUs is required to know
a multicast capable Intermediate System is attached to
subnetwork(s) that it originates multicast PDUs (i.e., to
the destination SNPA (subnet) address). An End System with Level 1
conformance is required to implement all parts of this
except for those supporting only Multicast Announcement. An
System is not required to know the current Multicast Address
to start originating multicast PDUs
Note: It is possible for End System not implementing
Address Mapping to successfully originate multicast PDUs (but
the End System knowing of the existence of a multicast
Intermediate System). Such operation may lead to
subnetworks use. Thus when an End System continues (or may continue
to originate multicast PDUs destined for the same group
implementations are to provide Multicast Address Mapping support
Level 2: full support for CLNP multicasting
Level 2 allows a host to join and leave host groups as well as
CLNP PDUs to host groups. It requires implementation by the
System of all parts of this specification
3. Group Network
Individual Network addresses used by CLNP for End System
are called Network Service Access Points (NSAPs). RFC 1237
the NSAP address for use in the Internet. In order to provide
address for a group of End Systems, this specification does
change the definition of the NSAP address, but adds a new type
identifier - the group Network address - that supports a
Network service (i.e., between a single source NSAP, identified by
individual Network address, and a group of destination NSAPs
identified by a group Network address). Host groups are identified
group Network addresses
In the development of multicast address extensions to CLNP
requirements were identified for: (1)"easily distinguishing"
addresses at the Network layer from NSAP addresses; (2)leaving
currently allocated address families unaffected and (3)ensuring
the approach taken would not require the establishment of
addressing authorities. In addition, it was agreed that
multicast options for all OSI Network layer users was desirable
Marlow [Page 4]
RFC 1768 CLNP Multicasting March 1995
thus the group Network addressing solution should support options
all address formats covered by ISO/IEC 8348 | CCITT
X.213. The only viable means identified for meeting all
was via creating a new set of AFI values with a fixed one-to-
mapping between each of the existing AFI values and a
group AFI value
Group Network addresses are defined by creating a new set of
values, one for each existing AFI value, and a fixed one-to-
mapping between each of the existing AFI values and a
group AFI value. The syntax of a group Network address is
to the syntax of an individual Network address, except that the
of the AFI in an individual Network address may be only one of
values already allocated for individual Network addresses,
the value of the AFI in a group Network address may be only one
the values allocated here for group Network addresses. The AFI
allocated for group Network addresses have been chosen in such a
that they do not overlap, in the preferred encoding defined
ISO/IEC 8348 | CCITT Recommendation X.213, with any of the AFI
that have already been allocated for individual Network addresses
3.1
group Network address: an address that identifies a set of zero
more Network service access points; these may belong to
Network entities, in different End Systems
individual Network address: an address that identifies a single NSAP
3.2 CLNP
A discussion of the CLNP address format is contained in RFC 1237.
structure of all CLNP addresses is divided into two parts the
Domain Part (IDP) and the Domain Specific Part (DSP). The first
octets of the IDP are the Authority and Format Identifier (AFI
field. The AFI has an abstract syntax of two hexadecimal digits
a value in the range of 00 to FF. In addition to identifying
address authority responsible for allocating a particular address
the format of the address, the AFI also identifies whether an
is an individual Network address or a group Network address.
are 90 possible AFI values to support individual Network
allocations. In addition, when the AFI value starts with the
"0" this identifies that the field contains an incomplete
Network address (i.e., identifies an escape code).
Table 1 allocates 90 possible AFI values to support group
address allocations. In addition if the first two digits of the
are hexadecimal FF, this indicates the presence of an
Marlow [Page 5]
RFC 1768 CLNP Multicasting March 1995
group Network address. The allocation of group addresses
restricted to be only from the AFI values allocated for
assignment of group addresses in Table 1. An addressing authority
allocating either Network addresses or authorizing one or
authorities to allocate addresses, allocates both individual and
corresponding group addresses. Thus each block of addresses
by an addressing authority (or its sub-authority) contains a block
individual Network addresses and group Network addresses.
individual and group address block allocated are differentiated
the AFI values used which are related as shown in Table 1.
Group Network addresses are only used as the destination
parameter of a CLNP PDU. Source Address parameters are
permitted to be group Network addresses
Table 2 lists the AFI values which have not been assigned, at
time, for the support of neither individual nor group
allocation. Future assignment of these AFI values is possible
Additional information concerning individual Network addresses (i.e.,
NSAP and NET (Network Entity Titles)) is contained in RFC 1237.
Note: While the format of the Initial Domain Part of a group
address is assigned, the format for the Domain Specific Part of
group Network address is specified by an addressing authority and
out of the scope of this memo. While NSAP address assignments
typically made to support hierarchical unicast routing, a
consideration for group Network address assignments may not exist
Marlow [Page 6]
RFC 1768 CLNP Multicasting March 1995
TABLE 1 - Relationship of AFI Individual and Group
-----------------------------------------------------------
|Individual Group | Individual Group | Individual Group |
-----------------------------------------------------------
| 0x FF | | |
| 10 A0 | 40 BE | 70 DC |
| 11 A1 | 41 BF | 71 DD |
| 12 A2 | 42 C0 | 72 DE |
| 13 A3 | 43 C1 | 73 DF |
| 14 A4 | 44 C2 | 74 E0 |
| 15 A5 | 45 C3 | 75 E1 |
| 16 A6 | 46 C4 | 76 E2 |
| 17 A7 | 47 C5 | 77 E3 |
| 18 A8 | 48 C6 | 78 E4 |
| 19 A9 | 49 C7 | 79 E5 |
| 20 AA | 50 C8 | 80 E6 |
| 21 AB | 51 C9 | 81 E7 |
| 22 AC | 52 CA | 82 E8 |
| 23 AD | 53 CB | 83 E9 |
| 24 AE | 54 CC | 84 EA |
| 25 AF | 55 CD | 85 EB |
| 26 B0 | 56 CE | 86 EC |
| 27 B1 | 57 CF | 87 ED |
| 28 B2 | 58 D0 | 88 EE |
| 29 B3 | 59 D1 | 89 EF |
| 30 B4 | 60 D2 | 90 F0 |
| 31 B5 | 61 D3 | 91 F1 |
| 32 B6 | 62 D4 | 92 F2 |
| 33 B7 | 63 D5 | 93 F3 |
| 34 B8 | 64 D6 | 94 F4 |
| 35 B9 | 65 D7 | 95 F5 |
| 36 BA | 66 D8 | 96 F6 |
| 37 BB | 67 D9 | 97 F7 |
| 38 BC | 68 DA | 98 F8 |
| 39 BD | 69 DB | 99 F9 |
-----------------------------------------------------------
Marlow [Page 7]
RFC 1768 CLNP Multicasting March 1995
TABLE 2 - AFI values reserved for future
--------------
| 1A-1F |
| 2A-2F |
| 3A-3F |
| 4A-4F |
| 5A-5F |
| 6A-6F |
| 7A-7F |
| 8A-8F |
| 9A-9F |
| FA-FE |
--------------
4. Model of a CLNP End System Multicast
The use of multicast transmission by a CLNP End System
extensions to two protocols: CLNP and the ES-IS Routeing Protocol.
provide level 0 service (no support for CLNP multicast),
extensions to these two protocols are required. To provide level 1
service (support for sending but not receiving CLNP multicast PDUs
all extensions contained in the following sections are
except for those supporting only Multicast Announcement. In order
support level 2 service (full support for CLNP multicasting),
extensions contained in the following sections are required
Extensions identified for Intermediate Systems are not required (
appropriate) for End Systems. Multicast transmission also
the use of a group Network address (as previously described) as
destination address parameter
5. Extensions to the CLNP
This section provides extensions to the CLNP Protocol [CLNP]
8473-1, to support multicast transmission. These additions
procedures for the connectionless transmission of data and
information from one network-entity to one or more peer network
entities
In developing the multicast extensions for CLNP a decision was
on how to "mark" a packet as multicast (versus the current
packets). Such marking is necessary since the forwarding
for multicast packets is different (e.g., multiple copies of a
may need to be forwarded). The two alternatives considered were
mark the packet (via a particular field) or to mark the
address, in the end both were done. The destination address for
multicast PDU identifies a host group which is of a very
nature than the unicast NSAP address. Rather than changing
Marlow [Page 8]
RFC 1768 CLNP Multicasting March 1995
nature of NSAP addresses, a new set of addresses were created
group Network addresses which are marked within the first
(i.e., the AFI field) with values reserved for group
addresses
Consideration was given to no further marking of the PDU; however,
problem was identified with only using the group Network address
identify multicast packets. Currently routers implementing the IS-
Intra-Domain protocol as Level 1 routers when receiving a packet
an unknown destination address are permitted to either discard
packet or send it to a Level 2 router. Such actions by non-
capable routers to multicast packets can lead to non-
behavior. Level 1 routers upon receiving a packet containing a
Network address might pass the packet up to a Level 2 router (
may or may not be multicast capable) or it might discard it
Depending upon the circumstances this might lead to whole
missing packets or packet duplication (possibly even explosion).
result was to seek deterministic behavior by non-multicast
routers by creating a new PDU type (Multicast Data PDU) and
into the CLNP reasons for discard: receiving a PDU of unknown type
Note that this reason for discard is mandatory on multicast
and non-multicast capable CLNP implementations
5.1
multicast: Data transmission to one or more destinations in
selected group in a single service invocation
multicast capable Intermediate System: An Intermediate System
incorporates the multicast features of the Network layer
5.2
The destination address parameter of a multicast PDU shall contain
group Network address. The source address parameter shall be
individual Network address
5.3 Extensions to the current protocol
In order to support multicast transmissions the following
CLNP protocol functions will be implemented
5.3.1 Header Format Analysis
The header format analysis function optionally provides
to Network entities which support multicast transfer to
applicable PDUs directly to End Systems served by such a
entity as well as to forward such PDUs on to other Network entities
Marlow [Page 9]
RFC 1768 CLNP Multicasting March 1995
This optional functionality is realized through a Network entity
multicast capability identifying a PDU as using multicast
via the PDU type and the PDU's destination address field
If a Network entity supports multicast transmission, then the
format analysis function shall provide checking to ensure that a
does not contain a group Network address in the source address field
Any PDU header analyzed to have a group address in the source
field shall be discarded
5.3.2 Route PDU
The route PDU function optionally provides capabilities to
entities which support multicast transfer for determining
Network entities to which a single PDU shall be forwarded to.
may result in multiple invocations of the forward PDU function
hence the need to make multiple copies of the PDU. For PDUs that
received from a different Network entity, the optional
for the route PDU function is realized as a result of the
format analysis function's recognition of the PDU as being
multicast PDU. A Network entity attached to more than one
when originating a multicast PDU is permitted to originate the PDU
more than one subnetwork
Note: The ES-IS function "Extensions to the ISO CLNP Route
by End Systems" discussed in section 6.10 identifies on
subnetworks an End System attached to more than one subnetwork
originate multicast PDUs on
Note: The purpose in allowing an originating Network entity
originate a multicast PDU on multiple subnetworks is to support
development of multicast IS-IS protocols which will need to
on which subnetworks a multicast PDU has visited. This behavior
predicated on the assumption that the Intermediate Systems in the
environment performing multicast forwarding form a connected set
5.3.3 Forward PDU
This function issues an SN-UNITDATA request primitive, supplying
subnetwork or Subnetwork Dependent Convergence Function (SNDCF
identified by the route PDU function with the protocol data unit
user data to be transmitted, the address information required by
subnetwork or SNDCF to identify the "next" system or systems
the subnetwork-specific addressing domain (this may be one or
Intermediate Systems and/or one or more destination End Systems),
quality of service constraints (if any) to be considered in
processing of the user data
Marlow [Page 10]
RFC 1768 CLNP Multicasting March 1995
5.3.4 Discard PDU
Add an additional reason for discard - a PDU is received with
unknown type code
5.3.5 Error reporting
It is important to carefully control the use of the error
capability in the case of multicast transfers. The primary
is to avoid the occurrence of broadcast storms and thus a
PDU may not cause the origination of another multicast PDU. This
the primary reason that the source address is not permitted to be
group address. In addition, a multicast PDU with error
permitted can result in flooding the source network-entity (as
as the networks used) with Error Report PDUs
While error reports are permitted on multicast PDUs, a PDU with
group Network address in the source address field shall not
responded to with an Error Report. This is to ensure that a
PDU does not generate another multicast PDU. If the source address
identified as a group address then an error report PDU shall not
generated and the original PDU shall be discarded
5.3.6 Source routing
No source routing capability is provided for multicast PDU transfer
The NS provider shall not accept a multicast PDU with source
parameters
5.4 Scope control
5.4.1
The scope control function is an option for multicast PDU
only. The scope control function allows the originator to limit
forwarding of the multicast PDU. The scope control function
the capability to limit the relaying of a particular PDU based on
individual Network addressing hierarchy and/or limit the amount
multicast expansion which can take place. In cases where both
of scope control are applied to the same PDU, forwarding will
once either has reached its scope control limit
5.4.2 Prefix Based Scope
The prefix based scope control function allows the originator
specify a specific set of address prefixes where the
forwarding of a PDU by an Intermediate System occurs only if one
the prefixes matches the Network Entity Title (NET) of
Marlow [Page 11]
RFC 1768 CLNP Multicasting March 1995
Intermediate System. Prefix based scope control may be selected
by the originator of a PDU. Prefix based scope control
accomplished using one or more address prefixes held in a
within the options part of the PDU header. The length of
parameter is determined by the originating network entity, and
not change during the lifetime of a PDU
When an Intermediate System receives a multicast PDU containing
prefix based scope control parameter, forwarding is only performed
every octet of one of the prefixes contained in the prefix
scope control parameter matches that Intermediate System's NET
starting from the beginning of its NET. If no such prefix
exists, the Intermediate System discards the PDU. The error
function shall not be invoked upon PDU discard
5.4.3 Radius Scope
The radius scope control function allows the originator to specify
maximum logical distance where multicast expansion can occur. It
closely associated with the header format analysis function. Each
receiving a multicast PDU which is capable of expanding and
contains a Radius Scope Control parameter, decrements the
Scope Control field in the PDU by an administratively set
between 0 and the maximum value of the field. An IS, when
decrements the Radius Scope Control field, shall place a value of 0
into this field if its current value is less than the amount it is
decrement by. This function determines whether the PDU received
be forwarded or whether its Radius has been reached, in which case
shall be discarded. An Intermediate System shall not forward
multicast PDU containing a Radius Scope Control parameter with
value of 0. The error reporting function shall not be invoked
PDU discard
5.4.3.1 Radius Scope Control
The Radius Scope Control parameter is useful where policies have
established across the potential forwarding path. One
policy for Internet use is for multicast capable routers to
this field as a hop count within a domain (decrement by one unit)
for inter-domain routers to either decrement this field to an
multiple of 256 when crossing domains where prior agreements
been made or decrement this field to 0 (i.e., discard the packet)
other domains
Marlow [Page 12]
RFC 1768 CLNP Multicasting March 1995
5.5 Structure and Encoding of
Multicast transmission is accomplished via the transfer of
Data (MD) PDUs. The PDU type code for a MD PDU is "1 1 1 0 1".
format of the MD PDU is identical to that of the Data (DT) PDU.
MD and DT PDU may contain the same optional parameters with
following exceptions: (1)The source routing parameter is
within DT PDUs but not MD PDUs; and (2)The scope control parameter
permitted within MD PDUs but not DT PDUs
5.6 Optional parameters for multicast
5.6.1 Prefix Based Scope
The prefix based scope control parameter specifies one or
address prefixes for which Intermediate System forwarding requires
match of one of the contained prefixes with the beginning of
Intermediate System's NET
Parameter Code: 1100 0100
Parameter Length:
Parameter Value: a concatenation of address prefix
The parameter value contains an address prefix list. The
consists of variable length address prefix entries. The first
of each entry gives the length of the address prefix denominated
bits that comprises the remainder of the entry. If the length
does not specify an integral number of octets then the prefix
is followed by enough trailing zeroes to make the end of the
fall on an octet boundary. The list must contain at least one entry
The prefix shall end on a boundary that is legal in the
syntax of the address family from which it is derived. For example
the encoding of a prefix whose DSP is expressed in decimal
must end on a semi-octet boundary, while the encoding of a
whose DSP is expressed in binary syntax can end on an arbitrary
boundary. If the end of the prefix falls within the IDP, then
prefix must end on a semi-octet boundary and must not contain
padding characters
Note: The length of the prefix based scope control parameter
determined by the originator of the PDU and is not changed during
lifetime of the PDU
Marlow [Page 13]
RFC 1768 CLNP Multicasting March 1995
5.6.1.1 Prefix
A prefix that extends into the DSP shall be compared directly
the encoded NET address, including any padding characters that may
present. A prefix which does not extend into the DSP shall
compared against the derived quantity NET', which is obtained
the NET address by removing all padding characters (as defined by
binary encoding process of ISO 8348).
The existence of a match shall be determined as follows
a) If the encoded NET (or NET') contains fewer bits than the pre
fix, then there is no match
b) If the encoded NET (or NET') contains at least as many bits
the prefix, and all bits of the prefix are identical to
corresponding leading bits of the encoded NET (or NET'),
is a match. Otherwise, there is no match
5.6.2 Radius Scope
The radius scope control parameter specifies the logical
that a multicast PDU can be forwarded
Parameter Code: 1100 0110
Parameter Length: two
Parameter Value: two octets which represents the
distance, that the PDU can be forwarded
in administratively set units
5.7 Provision of the Underlying
For a subnetwork that provides an inherent multicast capability,
is the functionality of the SNDCF to provide the mapping
group Network addresses and the corresponding addressing
of the subnetwork
5.8
All of the extensions provided to the functions to support
capability are optional. For an End System or Intermediate
which is not multicast capable these extensions are not applicable
An implementation claiming conformance as a multicast capable
System shall meet all of the requirements for an End System which
not multicast capable and also provide all of the
extensions provided here. An implementation claiming conformance as
Marlow [Page 14]
RFC 1768 CLNP Multicasting March 1995
multicast capable Intermediate System shall meet all of
requirements for an Intermediate System which is not
capable and also provide all of the multicast extensions
here
6. Extensions to the ES-IS Routeing
This section provides optional extensions to the ES-IS
Protocol [ES-IS], ISO 9542 to support the transfer of multicast PDUs
It is an explicit goal of this specification that ESs and ISs,
of which will have multicast capabilities and some without, will
able to fully function on the same subnetworks. This
does not change any aspect of a currently defined (i.e., non
multicast) ISO 9542 implementation, it adds new
functionality not modifying current functionality. Two
functions are provided: multicast announcement and multicast
mapping
6.1 Overview of the
6.1.1 Operation of ESs receiving multicast
ESs, upon initialization and periodically thereafter, will
End System Group Hello (ESGH) PDUs identifying, by particular
Network addresses, the multicast PDUs it wishes to receive. The
will periodically originate (announce) these ESGH PDUs on
subnetwork it wishes to receive these on. Reporting the same
Network address on multiple subnetworks may result in the
of duplicate PDUs. ES-IS operations related to requesting the
group Network address on multiple subnetworks are handled
independently (e.g., using different logical timers,...). It
permitted for an ES to report a number of group Network addresses
the same ESGH PDU. The only restrictions placed on
multiple group Network addresses within the same ESGH PDU are
all packets requested are to be received on the same subnet, with
same holding time and that the ESGH PDU be of length equal to or
that its maximum packet size constraint. Note that each
Network address in the ESGH PDU is paired with its own
(subnetwork point of attachment) address
An ES will always have an SNPA address associated with each of
active group Network addresses. An SNPA address is a
address, in the case of a subnetwork which uses IEEE 802
the SNPA address is a 48 bit IEEE 802 MAC (media access control
address. Of particular interest is the address used to mark
destination group. For a subnetwork using IEEE 802 addressing
group SNPA address uses a particular bit position to "mark"
SNPA addresses
Marlow [Page 15]
RFC 1768 CLNP Multicasting March 1995
Upon initialization the ES may have static SNPA address
(Pre-configured SNPA addresses). For any group Network
without a Pre-configured SNPA address that the ES wishes to receive
the ES will associate the "All Multicast Capable End Systems"
address. Upon receiving a Multicast Address Mapping (MAM)
containing a group Network address that the ES is announcing, the
will use the SNPA address pairing contained in the MAM PDU for
group Network address. Upon the expiration of the Mapping
Timer, the ES shall revert back to associating either the Pre
configured SNPA address if one exists or the "All Multicast
End Systems" SNPA address for the specific group Network address
While an ES is permitted to listen in on other ESs
(needed for the damping option), an ES is not permitted to change
group Network address to SNPA address mapping based on
announcement of other ESs
Optionally, the ES may perform damping (resetting a
Announcement Timer corresponding to a particular group
address) if the conditions necessary to withhold a
announcement are met. In order to perform damping the
conditions must be met: (1)The ES must be processing other ES'
announcements; (2)An ESGH PDU is received that identifies the
same group Network address and SNPA address pairing on a
subnetwork that this ES is announcing on; (3) The Multicast
Timer parameter value in the ESGH PDU received is equal to or
than the Multicast Holding Timer value, for this subnetwork, that
being used by the ES processing this ESGH PDU
ESs will utilize a local default value for their
Announcement Timer to control the period for sending out their
PDUs. The Active Multicast IS, if one exists on a
subnetwork, may suggest a value for ESs on the subnetwork to use
their Multicast Announcement Timer for a specific group
address. In order to support the optional damping function, ESs
required to incorporate a 25% jittering to the timer values that
are using
6.1.2 Operation of ESs originating multicast
The ES originating multicast packets identified by a specific
Network address is not required to be a receiver of such packets (
thus is not announcing that particular group Network address).
origination of multicast PDUs involves two differences to
origination of unicast PDUs. The two differences are: (1)
mechanism for selecting a destination SNPA address and (2)For
Systems attached to more than one subnet, the decision on
subnet(s) to originate the PDUs
Marlow [Page 16]
RFC 1768 CLNP Multicasting March 1995
The destination SNPA address used for originating each
packet depends on whether there is a multicast capable IS attached
the subnetworks. When a multicast capable IS is attached,
decision depends on whether there is multicast address
information available for that subnetwork corresponding to the
Network address used as the destination address parameter of
multicast packet. When there is a multicast capable IS attached to
subnetwork and there is multicast address mapping
available corresponding to the group Network address, then the
address obtained from the multicast address mapping information
used. Originating multicast packets using the destination
address used for receiving such multicast packets ensures that
multicast packets will not require additional forwarding on
originating subnetwork(s). When there is a multicast capable
attached to a subnetwork but for which there is no multicast
mapping information available corresponding to the the group
address, then the SNPA address used is the "All Multicast
Intermediate Systems" address
When there is no multicast capable IS attached to a subnetwork
the ES originating a multicast PDU uses pre-configured information
it is available or the "All Multicast Capable End Systems"
address when no pre-configured information is available
ES's attached to more than one subnetwork forward each
packet that they originate onto every attached subnetwork for
the NSAP address being used as the source address of the
packet is actively being reported through the unicast ES-IS
Configuration function
6.1.3 Operation of the Active Multicast
The Active Multicast IS listens in on all ESGH PDUs originated on
subnetwork for which it is serving as the Active Multicast IS.
subnetworks are handled independently (even if multiple
have the same ESs attached and the IS is serving as the
Multicast IS for these subnetworks).
The Active Multicast IS originates MAM PDUs, for all group
addresses for which it has received ESGH PDUs, on the subnetwork
to the following operational conditions
1) The IS initializes either as the Active Multicast IS after
election with other multicast capable ISs or
believing it is the only multicast capable IS
Note: The determination of such conditions is outside of the scope
this specification
Marlow [Page 17]
RFC 1768 CLNP Multicasting March 1995
2) The IS receives an ESGH PDU with a group Network address
to an incorrect SNPA address
3) The expiration of the IS's Multicast Address Mapping Timer
that group Network address;
Note: This is to prevent the expiration of Mapping Holding Timers
ESs
4) The IS receives a multicast PDU originated on the
which used an incorrect destination SNPA address
Note: Of particular concern are those multicast packets using
"All Multicast Capable Intermediate Systems" SNPA address
another SNPA address should have been used. In addition
multicast capable ISs are responsible for listening in on
multicast packets using destination SNPA addresses that are
within the current multicast address mapping information
As a result of the event driven conditions (i.e., conditions 2 or 4
above), the Active Multicast IS sends a MAM PDU with
information (i.e., not needing analysis of the Mask parameters).
Active Multicast IS limits the number of MAM PDUs that are sent
per unit of time. Particular MAM PDUs with direct information
not be sent more than once per second. MAM PDU will be sent
response to continuing event driven conditions such that
occurring greater than 10 seconds after the issuance of such a
PDU will result in the issuance of another MAM PDU
The Active Multicast IS is responsible for forwarding a
packet back on the subnetwork it was originated when a
packet used the "All Multicast Capable Intermediate System"
address when another SNPA address should have been used. A
forwarded back onto the subnetwork the multicast packet
originated on will be given a CLNP Lifetime of "1" to prevent
continued relaying of duplicate packets by the multicast ISs
The further relaying of any multicast packet originated on
subnetwork is the responsibility of the multicast routing
used and is outside the scope of this specification
6.2
Active Multicast IS: The one multicast capable IS selected (via
outside of this specification) to originate Multicast Address
information on a particular subnetwork
Marlow [Page 18]
RFC 1768 CLNP Multicasting March 1995
Paired SNPA Address: The SNPA address associated with a
group Network address on a specific subnetwork
6.3 Routing information supporting multicast
6.3.1 Multicast Announcement
An IS should forward a multicast PDU containing a
destination group Network address onto a subnetwork to which it
attached if and only if one or more of the ESs attached to
subnetwork have declared an interest in receiving multicast
destined for that group Network address. Multicast
information enables an IS that supports CLNP multicast to
discover, for each subnetwork to which it is attached, the
Network addresses for which ESs attached to that subnetwork
declared an interest
On a point-to-point subnetwork the multicast announcement
informs the Network entity, in the case where it is attached to
End System, of the group Network addresses for which that End
expects to receive multicast PDUs
On a broadcast subnetwork the multicast announcement
informs the multicast capable Intermediate Systems, of the
Network addresses for which ESs attached to that subnetwork expect
receive multicast PDUs
Note: Intermediate Systems with the optional OSI
capabilities do receive information identifying the SNPA address
ESs on the broadcast network that want PDUs with particular
Network addresses as their destination address; however, the
information is which multicast PDUs are needed, not which ESs
them
6.3.2 Multicast Address Mapping
In order to receive multicast packets destined for a particular
Network address, an ES may need to associate with the group
address a specific SNPA address. Multicast address
information enables an IS to inform ESs that they can
multicast packets destined for a particular group Network address
a corresponding specific SNPA address. In addition,
address mapping information may provide the specific destination
addresses needed by an ES for originating multicast packets
Multicast address mapping information is not employed on point-to
point subnetworks
Marlow [Page 19]
RFC 1768 CLNP Multicasting March 1995
Multicast address mapping information is employed on broadcast sub
networks to enable multicast capable Intermediate Systems to
the multicast capable End Systems that they can receive, on
specific broadcast subnetwork, multicast packets destined for
particular group Network address on a corresponding specific
address. In addition multicast address mapping information
the specific destination SNPA address, that corresponds to
particular group Network address, for each multicast packet that
originates on a specific broadcast subnetwork
6.4
All exchanges using this protocol are accomplished over a
subnetwork. While the control PDU's contain Network addresses (i.e.,
group Network addresses) actual control PDU transfer is
via Subnetwork based group addresses (i.e., group SNPA addresses).
The following group SNPA addresses are used: (1)All Multicast
End Systems; (2)All Multicast Announcements; (3)All Multicast
Intermediate Systems and (4)a group SNPA address corresponding to
group Network
6.5
Two additional timers are employed: (1)the Multicast
Timer (MAT) and (2)Multicast Address Mapping Timer (MAMT).
multicast announcement or multicast address mapping information
be discarded after the Holding Timer expires to ensure the
operation of the protocol
6.5.1 Multicast Announcement
The Multicast Announcement Timer is a local timer (i.e.,
independently by each End System, one timer per group
address) which assists in performing the Report
Announcement function. The timer determines how often an End
reports its desire to receive multicast PDUs with that group
address as its destination address parameter. Considerations
setting this timer are similar to those described for
Configuration timer in the ES-IS specification
6.5.2 Multicast Address Mapping
The Multicast Address Mapping Timer is a local timer (i.e.,
maintained independently by an Intermediate System which is
participating with End Systems to transfer multicast PDUs)
assists in performing the Report Multicast Address Mapping function
The timer determines how often an Intermediate System,
participating with End Systems for the transfer of multicast PDUs
Marlow [Page 20]
RFC 1768 CLNP Multicasting March 1995
reports the Multicast Address Mapping for a particular group
address. The shorter the Multicast Address Mapping Timer, the
quickly End Systems on the subnetwork will become aware of
correct address mapping which may change due to the
System becoming available or unavailable. There is a trade
between increased responsiveness and increased use of resources
the subnetwork and in the End Systems
6.6 Extensions to the current protocol
In order to support multicast transmissions the following
ES-IS protocol functions will be implemented
6.6.1 Report Configuration by Intermediate
All multicast capable Intermediate Systems on a subnetwork shall
the Multicast Capable option in all ISH PDUs that they originate
This will provide multicast capable End Systems with a way
determine that a multicast capable Intermediate System is
on a particular subnetwork
6.6.2 Query
Note: The Query Configuration function cannot be performed to
the corresponding SNPA address of a group Network address since
addressing information needed is the corresponding group SNPA
and not the SNPA address of a particular End System responding. On
large broadcast subnetwork, many different Configuration
could result each incorporating a different End System Address.
it is possible to design a Query Configuration for use
multicast, this function does not appear to be required given the
of the "All Multicast Capable End Systems" address for supplying
SNPA address when the group SNPA address is not known
6.7 Multicast
6.7.1 Report Multicast Announcement Function by End
An End System which needs to receive or continue to receive
multicast PDUs (i.e., PDUs with group Network addresses as
destination address), constructs and transmits ESGH PDUs to
multicast capable Intermediate Systems of the set of group
address destinations for which it wishes to receive PDUs. This may
done by constructing ESGH PDUs for each group Network address
Alternatively, ESGH PDUs may be constructed which convey
about more than one group Network address at a time, up to the
imposed by the permitted SNSDU size and the maximum header size
the ESGH PDU. Each ESGH PDU is transmitted by issuing an SN
Marlow [Page 21]
RFC 1768 CLNP Multicasting March 1995
UNITDATA.Request with the following parameters
SN_Userdata (SNSDU) <- ESGH
SN_Destination _Address <- multi-destination address that
"All Multicast Announcements
If an End System is attached to more than one subnetwork,
information about each group Network address desired for receiving
a particular subnetwork serving the End System shall be
via that subnetwork. It is permissible for an End System to
group Network addresses on multiple subnetworks; however,
multicast PDUs should be anticipated
The Group Address Pair parameter carries a list of Group
Addresses, each paired with its associated SNPA address.
information is used by the Active Multicast IS to determine whether
Multicast Address Mapping PDU should be emitted to update
association between Group Network Addresses and SNPA addresses
The Holding Time (HT) field is set to approximately twice the ES'
Multicast Announcement Timer (MAT) parameter. The value shall
large enough so that even if every other ESGH PDU is discarded (
to lack of resources), or otherwise lost in the subnetwork,
multicast announcement information will still be maintained.
value should be set small enough so that Intermediate
resources are not needlessly consumed when the ES no longer wishes
receive PDUs destined to a group Network address
Note: When combining multiple group Network addresses in a
ESGH PDU, it should be realized that there is a single Holding
parameter associated with all of these addresses
6.7.1.1 Generating Jitter on Multicast Announcement
The ES shall apply a 25% jitter to its Multicast Announcement
(MAT) parameter. When ESGH PDUs are transmitted as a result of
expiration, there is a danger that the timers of individual
may become synchronised. The result of this is that the
distribution will contain peaks. Where there are a large number
synchronised systems, this can cause overloading of both
transmission medium and the systems receiving the PDUs. In order
prevent this from occurring, all periodic timers, the expiration
which can cause the transmission of PDUs, shall have "jitter
introduced as defined in the following algorithm
Marlow [Page 22]
RFC 1768 CLNP Multicasting March 1995
Jitter = 25;
Resolution = 100;
(* The timer resolution in ms *)
PROCEDURE Random(max: Integer): Integer
(* This procedure delivers a Uniformly distributed
integer R such that 0 < R
PROCEDURE WaitUntil(time: Integer
(* This procedure waits the specified number
ms and then returns *)
PROCEDURE CurrentTime():
(* This procedure returns the current time in ms *)
DefineJitteredTimer(baseTimeValueInSeconds : Integer
expirationAction : Procedure);
baseTimeValue, maximumTimeModifier, waitTime : Integer
nextexpiration : Time
baseTimeValue := baseTimeValueInSeconds * 1000 / Resolution
maximumTimeModifier := baseTimeValue * Jitter / 100;
(* Compute maximum possible jitter *)
WHILE running
(*First compute next expiration time *)
randomTimeModifier := Random(maximumTimeModifier);
waitTime:= baseTimeValue - randomTimeModifier
nextexpiration := CurrentTime() + waitTime
(* Then perform expiration Action *)
expirationAction
WaitUntil(nextexpiration);
END (* of Loop *)
END (* of DefineJitteredTimer *)
Marlow [Page 23]
RFC 1768 CLNP Multicasting March 1995
Thus the call "DefineJitteredTimer(HelloTime, SendHelloPDU);"
"HelloTime" is 10 seconds, will cause the action "SendHelloPDU" to
performed at random intervals of between 7.5 and 10 seconds.
essential point of this algorithm is that the value
"randomTimeModifier" is randomised within the inner loop. Note
the new expiration time is set immediately on expiration of the
interval, rather than when the expiration action has been completed
The time resolution shall be less than or equal to 100 ms. It
recommended to be less than or equal to 10ms. The time resolution
the maximum interval than can elapse without there being any
in the value of the timer. The periodic transmission period shall
random or pseudo-random in the specified range. with
distribution across similar implementations
Note: Applying jitter to the MAT parameter is required in order
support the optional Damping function. If no jitter is applied on
subnetwork where many ESs are requesting a particular multicast
it is likely that they will have the same value for their MAT
these timers may all become synchronised. Such synchronisation
result in peaks in the distribution of traffic as described above
The resulting overloading of the transmission medium and the
receiving the PDUs will negate any beneficial use of the
function (since systems may be attempting to transmit their own
PDUs at the time they receive ESGH PDUs originated by other ESs
the same group Network address
6.7.2 Record Multicast Announcement
The Record Multicast Announcement function receives ESGH PDUs
extracts the multicast announcement information and updates
information in its routing information base
The receiving system is not required to process any option fields
a received ESGH PDU
Note: When a system chooses to process these optional fields,
precise actions are not specified by this International Standard
6.7.2.1 Record Multicast Announcement Function by Intermediate
On receipt of an ESGH PDU an IS with the optional
capabilities extracts the configuration information and stores
{group Network address, subnetwork} in its routing information
replacing any other information for the same entry
Marlow [Page 24]
RFC 1768 CLNP Multicasting March 1995
The Active Multicast IS upon receipt of an ESGH PDU also extracts
Paired SNPA Address parameter corresponding to each group
address in the ESGH PDU. If the Active Multicast IS has a mapping
a group Network address carried in the ESGH for which the paired
address does not match, the Report Multicast Address Mapping
is performed
6.7.2.2 Optional Damping
An ES with the optional capabilities to support multicast
may decide to process ESGH PDUs multicast by other End Systems.
is potentially some reduction in network traffic by doing this. An
requesting to receive multicast PDUs is permitted to reset
Multicast Announcement Timer corresponding to one group
address on one subnetwork upon receiving an ESGH PDU from another
under the following circumstances
a) The {group Network address, paired SNPA address} received on
particular subnetwork matches that of the ES processing the
PDU for that subnetwork
b) The Holding Timer parameter value in the ESGH PDU received
equal to or greater than the Holding Timer value for the,
Network address, being used by the ES processing this PDU
6.7.3 Flush Old Multicast Announcement
The Flush Old Multicast Announcement function is executed to
multicast announcement entries in its routing information base
Holding Timer has expired. When the Holding Timer for a group
address expires, this function removes the corresponding entry
the routing information base of the local IS for the
subnetwork
6.8 Multicast Address
6.8.1 Report Multicast Address Mapping Function by Intermediate
The Active Multicast Intermediate System constructs a MAM PDU
corresponding to a group Network address for which it received
the Record Multicast Announcement function, and issues these
under the following circumstances
a) The IS initializes either as the Active Multicast IS after
election with other multicast capable ISs or initializes
determining it is the only multicast capable IS (
determination of such conditions are outside of the scope
this standard),
Marlow [Page 25]
RFC 1768 CLNP Multicasting March 1995
b) The IS receives an ESGH PDU with a group Network address
to an SNPA address other than the SNPA address contained in
Active Multicast IS's multicast address mapping information
that group Network address,
Note: The Active Multicast IS determines which mappings are correct
Pre-configured mappings which are used prior to the initialization
the Active Multicast IS may be determined to be incorrect by
Active Multicast IS
c) The expiration of the IS's Multicast Address Mapping Timer
that group Network address
Note: This is to prevent the expiration of Holding Timers in ESs
d) The IS receives a multicast PDU originated on the
which used an incorrect destination SNPA address
Note: Of particular concern are those multicast packets using
"All Multicast Capable Intermediate Systems" SNPA address
another SNPA address should have been used. The
Subnetwork Forwarding function is performed if this event occurs (
section 6.11).
Note: The multicast capable ISs need to receive multicast packets
all SNPA addresses that are contained in the current
address mapping information for the subnetwork. The
capable ISs are not required to receive multicast packets on any
addresses other than those contained in the current multicast
mapping information and the "All Multicast Capable
Systems" SNPA address
Circumstances b) and d) are the event driven conditions for
Active Multicast IS to construct and issue a MAM PDU. The
Multicast IS shall limit the number of MAM PDUs issued per unit
time. MAM PDUs with identical information shall not be issued
than once per second. Event conditions occurring 10 seconds
the last issue of an appropriate MAM PDU shall result in the
of another such MAM PDU
The IS serving as the Active Multicast Intermediate System
construct a MAM PDU for each group Network address. Alternatively
MAM PDUs may be constructed which convey information about more
one group Network address at a time, up to the limits imposed by
permitted SNSDU size and the maximum header size of the MAM PDU.
IS performs all multicast address mapping functions independently
each of its subnetworks even if this IS is the Active Multicast IS
multiple subnetworks. Each MAM PDU is transmitted by issuing an SN
Marlow [Page 26]
RFC 1768 CLNP Multicasting March 1995
UNITDATA.Request with the following parameters
SN_Userdata (SNSDU) <- MAM
SN_Destination _Address <- multi-destination address that
"All Multicast Capable End Systems
The Holding Time (HT) field is set to approximately twice
Intermediate System's Multicast Address Mapping Timer (MAMT
parameter. This variable shall be set to a value large enough
that even if every other MAM PDU, for a particular group
address, is discarded (due to lack of resources), or otherwise
in the subnetwork, the multicast address mapping information
still be maintained. The value should be set small enough so that
Systems will quickly cease to use the multicast address
supplied by ISs that have failed
Note: -- The Holding Timer parameter value applies to all
Network addresses called out in the MAM PDU
The Group Address Pair parameter is used to convey the
between Group Network Addresses and SNPA addresses
Optionally, the Active Multicast IS may include information in
MAM PDU indicating a larger population of group Network addresses
which the same multicast address mapping information applies.
are two optional fields for this purpose: the Group Network
Mask option and the Paired SNPA Address Mask option
There are three permitted cases for including or excluding the masks
In the first case, both masks are absent. In this case the MAM
conveys information about one set of enumerated group
addresses only
Note: -- Multiple group address pairs may be contained in a
MAM PDU
In the second case, the MAM PDU contains a Group Network Address
but no Paired SNPA Address Mask. In this case, the MAM PDU
information about an equivalence class of group Network addresses
The information reveals that multiple group Network addresses
mapped to the same SNPA address
In the third case, the MAM PDU contains both masks. As in the
case, the MAM PDU conveys information about an equivalence class
group Network addresses. But in this case, the information
that the SNPA addresses for the equivalence class of group
address are embedded in the group Network address. In particular
Marlow [Page 27]
RFC 1768 CLNP Multicasting March 1995
Paired SNPA Address Mask indicates the location of the SNPA
in the group Network Address(es).
The Active Multicast IS shall construct a MAM PDU with
information, not needing analysis of the Mask parameters, in
to the occurrence of an event driven condition. The Active
IS may provide additional information in such a MAM PDU via the
of Mask parameters
An IS may suggest a value for End Systems on the local subnetwork
use as their Multicast Announcement Timers, for a specific
Network address, by including the Suggested ES Multicast
Timer (ESMAT) parameter in the transmitted MAM PDU. Setting
parameter permits the Active Multicast IS to influence the
with which ESs transmit ESGH PDUs
Note: If the ESMAT parameter is used, the one value permitted in
MAM PDU is suggested for all group Network addresses called out
the MAM PDU
6.8.2 Record Multicast Address Mapping Function by End
The Record Multicast Address Mapping function receives MAM PDUs
extracts the multicast address mapping information and updates
information in its routing information base. The receiving system
not required to process any option fields in a received MAM PDU
the exception of the Suggested ES Multicast Announcement
(ESMAT) parameter
Note: When a system chooses to process these optional fields,
precise actions are not specified by this International Standard
On receipt of a MAM PDU an ES with the optional
capabilities extracts the multicast address mapping information
stores the {group Network address, paired SNPA address} for
particular subnetwork in its routing information base replacing
other information for the same group Network address and subnetwork
In addition, an ES shall set its Multicast Announcement Timer
corresponding to the group Network address for which it is
the Record Multicast Address Mapping function, based on receipt of
MAM PDU, corresponding to that group Network address, containing
ESMAT parameter
Note: While an ES may process ESGH PDUs multicast by other ESs
support the optional Damping function, an ES is not permitted
change its own mapping due to the mapping found in other ES's
PDUs
Marlow [Page 28]
RFC 1768 CLNP Multicasting March 1995
6.8.3 Flush Old Multicast Address Mapping Function by End
The Flush Old Multicast Address Mapping function is executed
remove multicast address mapping entries in its routing
base whose corresponding Holding Timer has expired. When such
Holding Timer for a multicast address mapping expires, this
removes the corresponding entry from its routing information base
the corresponding SNPA
6.9 Paired SNPA Address Selection Function by End
An End System shall pair each group Network address with
associated SNPA address to support receiving (e.g., performing
Report Multicast Announcement function) and originating
PDUs
6.9.1 Paired SNPA Address Selection for Receiving Multicast
An End System always has a paired SNPA address for every active
Network address on a particular subnetwork. This mapping is
by
a) recording a multicast address mapping which is maintaining
active holding timer, or if there has been no
information received,
b) having pre-configured multicast address mapping information,
if neither dynamic nor pre-configured information is available
c) mapping the "All Multicast Capable End Systems" multi
destination address to the group Network address
6.9.2 Paired SNPA Address Selection for Originating Multicast
An End System, originating a multicast PDU, pairs a SNPA address
the group Network address. This mapping is obtained in the
manner
a) If there is a multicast capable IS reachable on the
then the SNPA address used by an End System originating a multi
cast PDU is either the paired SNPA address obtained from
multicast address mapping information associated with the
Network address in the multicast PDU's Destination
parameter or if there is no valid entry for the group
address by using the "All Multicast Capable Intermediate Sys
tems" multi-destination address, or if there is no
capable Intermediate System on the subnetwork,
Marlow [Page 29]
RFC 1768 CLNP Multicasting March 1995
Note: Multicast address mapping information is valid if the
Timer associated with it has not expired
Note: An ES can determine if a multicast capable IS is reachable
the subnetwork by having for that subnetwork either (1)
address mapping information or (2)routing information received via
ISH PDU containing a Multicast Capable optional parameter. In
case the information must be valid (i.e., the Holding Timer for
information must not have expired).
b) having pre-configured multicast address mapping information,
if neither a multicast capable Intermediate System is present
the subnetwork nor pre-configured information is available,
c) mapping the "All Multicast Capable End Systems" multi
destination address to the group Network address
6.10 Extensions to the ISO CLNP Route Function by End
An End System attached to more than one subnetwork shall
when originating a multicast PDU whether to forward this
PDU to more than one subnetwork or not. End Systems shall
each multicast PDU on all subnetworks for which the ISO ES-
Configuration function is actively reporting the NSAP
contained in the Source Address parameter of the multicast PDU. As
result of this function multiple invocations of the ISO
Forwarding function may result when such an ES originates a
PDU
6.11 Originating Subnetwork Forwarding Function by
The Active Multicast IS upon receiving a multicast PDU originated
a subnetwork which used the "All Multicast Capable
Systems" SNPA address when another SNPA address should have
used, performs the Originating Subnetwork Forwarding function.
multicast address mapping information defines the correct
address pairings for a given subnetwork. The Originating
Forwarding function forwards the multicast PDU back on subnetwork
was originated on. In the case that the ES was attached to more
one subnetwork and originated the multicast PDU on more than
subnetwork, the Active Multicast IS for each subnetwork performs
Originating Subnetwork Forwarding function for the subnetwork
they are responsible for
The Active Multicast IS obtains the contents for the multicast
for the Originating Subnetwork Forwarding function by using
contents of the multicast PDU received with the incorrect
Marlow [Page 30]
RFC 1768 CLNP Multicasting March 1995
SNPA address and replacing the original PDU Lifetime field with
value one (0000 0001). The Active Multicast IS performs the ISO 8473
PDU Composition function and forwards the PDU to the subnetwork
the PDU was originated on using the ISO 8473 Forwarding function
the correct destination SNPA address
Note: The PDU Lifetime field is set to "one" to ensure that
attached to the originating subnetwork do not forward this PDU on
Such ISs should have received the PDU when it was originated
this function is only performed in the event of receiving a
PDU incorrectly addressed to the "All Multicast Capable
Systems" SNPA address
6.12 Structure and Encoding of
The ES-IS multicast control functions are supported via the
of ESGH and MAM PDUs. The one exception to this is that a
optional parameter, the Multicast Capable parameter, is provided
use within the ISH PDU
6.12.1 PDU Type
The Multicast Announcement is accomplished via the transfer of
System Group Hello (ESGH) PDUs. The PDU type code for an ESGH PDU
"0 0 1 0 1". The Multicast Address Mapping (MAM) is accomplished
the transfer of Multicast Address Mapping PDUs. The PDU type code
a MAM PDU is "0 0 1 1 1".
6.12.2 Hold Time
The Holding Time field specifies the maximum time for the
Network entity to retain the multicast announcement or
address mapping information contained in the PDU
6.12.3 Structure of Addressing
The ESGH and MAM PDUs carry one or more group Network
(GNAs) each with their associated Paired SNPA Address (PSA).
6.12.4 Group Address Pair Parameter for ESGH and MAM
The Group Address Pair parameter is a list of one or more
Network addresses each with their associated Paired SNPA address.
group Network address identifies specific multicast PDUs and
Paired SNPA address is the SNPA address on which the ES expects
receive such multicast PDUs on that subnetwork. It is encoded in
ESGH and MAM PDUs as shown in Figure 1.
Marlow [Page 31]
RFC 1768 CLNP Multicasting March 1995
,----------------------------------------------------,
| Number of Group Address Pairs | 10
|----------------------------------------------------|
| Group Network Address Length Indicator (GNAL) | 11
|----------------------------------------------------|
| | 12
: Group Network Address (GNA) :
| |
|----------------------------------------------------|
| Paired SNPA Address Length Indicator (PSAL) |
|----------------------------------------------------|
| |
: Paired SNPA Address (PSA) :
| |
|----------------------------------------------------|
| GNAL |
|----------------------------------------------------|
| |
: GNA :
| |
|----------------------------------------------------|
| PSAL |
|----------------------------------------------------|
| |
: PSA :
| | m-1
'----------------------------------------------------'
Figure 1 - ESGH and MAM PDUs - - Group Address Pair
6.12.5 Extensions to the current Option
The Security and Priority optional parameters may be carried in
ESGH PDU. There is no Security or Priority option for the MAM PDU
6.12.6 Suggested ES Multicast Announcement
The ESMAT parameter may appear only in the MAM
The ESMAT parameter conveys the value that an IS requests
receiving ESs to use as their local Multicast Announcement Timer
Parameter Code: 1100 0111
Parameter Length: two
Parameter Value: ESMAT in units of seconds
Marlow [Page 32]
RFC 1768 CLNP Multicasting March 1995
6.12.7 Multicast
The Multicast Capable option may appear only in the ISH
The Multicast Capable options consists only of a one octet code and
one octet parameter length field, there is no parameter field
Parameter Code: 1100 1000
Parameter Length: zero
Parameter Value: none (parameter does not exist).
6.12.8 Group Network Address
The Group Network Address Mask option may only appear in the MAM PDU
The Group Network Address Mask parameter indicates that the
address mapping information applies to a larger population of
Network Addresses than the group Network address(es) contained in
MAM PDU indicates. When this option is provided in a MAM PDU,
masking relationship contained must be valid for all group
addresses contained in this PDU. An End System may ignore
parameter
The Group Network Address Mask establishes an equivalence class
group Network addresses to which the same multicast address
information applies. To determine whether or not a trial
Network address falls within the equivalence class, the ES aligns
trial group Network address with the Group Network Address
padding the latter with trailing zero octets if necessary. If in
bit positions where the Group Network Address Mask is "1" the
group Network address matches the Group Network Address field of
Group Address Pair parameter of the MAM PDU, then the trial
Network address belongs to the equivalence class described by the
PDU
The Group Network Address Mask parameter has additional
when considered with the Paired SNPA Address Mask parameter
Parameter Code: 1110 0011
Parameter Length: variable, up to 20
Parameter Value: a comparison mask of octets to
aligned with the Group Network
field of the Group Address
parameter of the MAM PDU
Marlow [Page 33]
RFC 1768 CLNP Multicasting March 1995
6.12.9 Paired SNPA Address
The Paired SNPA Address Mask option may only appear in the MAM PDU
When the Paired SNPA Address Mask is present, the equivalence
defined by the Group Network Address Mask also has common
below the Group Network Address Mask; i.e., in the portion of
group Network address where the Group Network Address Mask
logically "0". The Paired SNPA Address Mask supplies
information about the structure, by indicating certain bit
within the space "below" the Group Network Address Mask
Specifically, the Paired SNPA Address Mask indicates the location
the Paired SNPA address in the Group Network Address
This parameter may appear in a MAM PDU only if the Group
Address Mask is also present. When this option is provided in a
PDU, the masking relationship contained must be valid for all
Network addresses contained in this PDU. An ES receiving such a
PDU may safely ignore both masks. However (since presence of
masks dictates different functional behavior than the presence of
Group Network Address Mask alone) an ES shall not ignore one of
masks while heeding the other
Parameter Code: 1110 0100
Parameter Length:
Parameter Value: a comparison mask of octets to
aligned with the Group Network
field(s) of the Group Address
parameter of the MAM PDU
6.12.9.1 Mask Parameters
This section provides examples of using the Group Network
Mask and the Paired SNPA Address Mask. The examples given are for
Internet usage of CLNP Multicasting across subnetworks using IEEE 802
addressing. For these examples the group Network address format is
+-----+----------------------------------------+
| IDP | Upper DSP | Embedded SNPA address | SEL
+-----+-----------+-----------------------+----+
octets: | 3 | 10 | 6 | 1 |
+-----+-----------+-----------------------+----+
Thus the group Network address used is 20 octets. For
examples, the only field considered is the Embedded SNPA
field and its placement within the group Network address
Marlow [Page 34]
RFC 1768 CLNP Multicasting March 1995
In the first example it is the policy in "this part of the Internet
to map the Embedded SNPA address into the IEEE 802 address
reserved by IEEE 802 for group addressing using LOCAL assignment
this corresponds to all 48 bit values with the two low order bits
the first octet set to "11".
The Active Multicast Intermediate System on this subnetwork
construct a MAM PDU to map, for this example, a group Network
of {13 octets, 03-00-DA-DA-DA-DA, 1 octet} and a paired SNPA
of 03-00-DA-DA-DA-DA. In addition the Active Multicast
System can include in the MAM PDU a Group Network Address Mask
FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-03-00-00-00-00-00-00.
With this parameter, all group Network addresses which share
identical first 13 octet and with "11" in the two low order bits
the 14th octet are put in an equivalence class and share the
mapping information. If this were the only option present then all
these group Network addresses would all have a paired SNPA address
03-00-DA-DA-DA-DA
In order to map the group Network addresses to the range of
addresses of this example, the MAM PDU must also contain a
SNPA Address Mask. The Paired SNPA Address Mask identifies where
SNPA Address is contained within the group Network addresses (
by the equivalence class formed by the Group Network Address
within the same PDU). For this example the Paired SNPA Address
is 00-00-00-00-00-00-00-00-00-00-00-00-00-FF-FF-FF-FF-FF-FF-00.
As a second example, all group Network addresses with a specific
(organizationally unique identifier) using the twenty octet
Network address format provided above are mapped to their
SNPA address. An OUI is assigned by IEEE 802 and is three octets
length. The OUI is contained in the first three address octets of
GLOBALLY assigned IEEE 802 address. For this example the MAM
must contain the following
1. A group Network address contained within the MAM PDU with
OUI of interest
2. A group Network address Mask of FF-FF-FF-FF-FF-FF-FF-FF-FF
FF-FF-FF-FF-FF-FF-FF-00-00-00-00.
3. A Paired SNPA Address of 00-00-00-00-00-00-00-00-00-
00-00-00-00-FF-FF-FF-FF-FF-FF-00.
6.12.10 End System Group Hello (ESGH)
The ESGH PDU has the format shown in figure 2:
Marlow [Page 35]
RFC 1768 CLNP Multicasting March 1995
,----------------------------------------------------,
| Network Layer Protocol Identifier | 1
|----------------------------------------------------|
| Length Indicator | 2
|----------------------------------------------------|
| Version/Protocol ID Extension | 3
|----------------------------------------------------|
| reserved (must be zero) | 4
|----------------------------------------------------|
| 0 | 0 | 0 | Type (00101 = ESGH) | 2
|----------------------------------------------------|
| Holding Time | 6,7
|----------------------------------------------------|
| Checksum | 8,9
|----------------------------------------------------|
| Number of Group Address Pairs | 10
|----------------------------------------------------|
| Group Network Address Length Indicator (GNAL) | 11
|----------------------------------------------------|
| | 12
: Group Network Address (GNA) :
| |
|----------------------------------------------------|
| Paired SNPA Address Length Indicator (PSAL) |
|----------------------------------------------------|
| |
: Paired SNPA Address (PSA) :
| |
|----------------------------------------------------|
| GNAL |
|----------------------------------------------------|
| |
: GNA |
| |
|----------------------------------------------------|
| PSAL |
|----------------------------------------------------|
| |
: PSA :
| | m-1
|----------------------------------------------------|
| |
: Options :
| | p-1
'----------------------------------------------------'
Figure 2 - ESGH PDU
Marlow [Page 36]
RFC 1768 CLNP Multicasting March 1995
6.12.11 Multicast Address Mapping (MAM)
The MAM PDU has the format shown in figure 3:
,----------------------------------------------------,
| Network Layer Protocol Identifier | 1
|----------------------------------------------------|
| Length Indicator | 2
|----------------------------------------------------|
| Version/Protocol ID Extension | 3
|----------------------------------------------------|
| reserved (must be zero) | 4
|----------------------------------------------------|
| 0 | 0 | 0 | Type (00111 = MAM) | 2
|----------------------------------------------------|
| Holding Time | 6,7
|----------------------------------------------------|
| Checksum | 8,9
|----------------------------------------------------|
| Number of Group Address Pairs | 10
|----------------------------------------------------|
| Group Network Address Length Indicator (GNAL) | 11
|----------------------------------------------------|
| | 12
: Group Network Address (GNA) :
| |
|----------------------------------------------------|
| Paired SNPA Address Length Indicator (PSAL) |
|----------------------------------------------------|
| |
: Paired SNPA Address (PSA) :
| |
|----------------------------------------------------|
| GNAL |
|----------------------------------------------------|
| |
: GNA :
| |
|----------------------------------------------------|
| PSAL |
|----------------------------------------------------|
| |
: PSA :
| | m-1
Marlow [Page 37]
RFC 1768 CLNP Multicasting March 1995
|----------------------------------------------------|
| |
: Options :
| | p-1
'----------------------------------------------------'
Figure 3 - MAM PDU
6.13
All of the extensions provided to the functions to support
capability are optional. For an End System or Intermediate
which is not multicast capable these extensions are not applicable.
Network entity may choose to be multicast capable, a
capable Network entity is required to support both
announcement information and multicast address mapping information
An implementation claiming conformance as a multicast capable
System shall meet all of the requirements for an End System which
not multicast capable and shall support multicast
information and shall implement the functions marked as Mandatory (M
in column 4 of table 3. A multicast capable End System
shall also support multicast address mapping information and
implement the functions marked as Mandatory (M) in column 5 of
3.
An implementation claiming conformance as a multicast
Intermediate System shall meet all of the requirements for
Intermediate System which is not multicast capable and shall
multicast announcement information and shall implement the
marked as Mandatory (M) in column 6 of table 3. A multicast
Intermediate System implementation shall also support
address mapping information and shall implement the functions
as Mandatory (M) in column 7 of table 3.
Marlow [Page 38]
RFC 1768 CLNP Multicasting March 1995
Table 3 - Static Conformance Requirements for Multicast
Network
ES
Clause --------------
Label Function Reference AI MI AI
------------------------------------------------------------------
RpMAn Report Multicast Announcement 6.7.1 M - - -
RcMAn Record Multicast Announcement 6.7.2.1 - - M -
RcDamp Record Damping 6.7.2.2 O - - -
FlMAn Flush Old Multicast Announcement 6.7.3 O - M -
RpMAdMa Report Multicast Address Mapping 6.8.1 - - -
MATGn ESMAT Generation 6.8.1 - - -
RcMAdMa Record Multicast Address Mapping 6.8.2 - M - -
MATPr ESMAT Processing 6.8.2 - M - -
FlMAdMa Flush Old Multicast Address Map 6.8.3 - M - -
PSAdSel Paired SNPA Address Selection 6.9.1 - M - -
ExtForw Extensions to CLNP Route Function 6.10 - M - -
OSuForw Originating Subnetwork Forwarding 6.11 - - -
Key
AI = Multicast Announcement information
MI = Multicast Address Mapping information
M = Mandatory; O = Optional; - = not
7. Security
Security issues are not discussed in this memo
Marlow [Page 39]
RFC 1768 CLNP Multicasting March 1995
Appendix A. Differences with RFC 1112
This appendix is intended to identify differences between
mechanisms defined for CLNP Multicast in this specification and
for IP multicast defined in RFC 1112. The work on CLNP
followed the work on IP multicast and was explicitly aimed
bringing the capabilities described in RFC 1112 into a CLNP context
This appendix is intended to provide some background information
the difference; however, it is not intended to justify the
selected for CLNP multicast use
Static/Dynamic Address Binding of Multicast
IP multicast utilizes a static binding of Class D IP addresses to
specific range of IEEE 802 48 bit group addresses. The IEEE 802
address range that is used is within the address range that IEEE 802
allocates for "Global" administration and this block of addresses
under the control of the Internet Assigned Numbers Authority (IANA
which in turn has allocated this block of addresses for use by
multicast. This scheme is very simple and efficient. Given the
of a 32 bit IP address, the lower 23 bits of the Class D address
mapped into the lower 23 bits of a 48 bit IEEE 802 address where
upper 25 bits are fixed. Static binding of this form is global
scope (all members of a group use the same IEEE 802 address on
subnets (at least all that use IEEE 802 addressing).
CLNP multicast uses a dynamic binding of a group Network address (
to 20 bytes) to any subnetwork address. In cases where no
capable Intermediate Systems are attached to a subnetwork then
binding using preconfigured information or the "All Multicast
End Systems" subnetwork addresses is used. The large GNA provides
room to contain a full 48 bit IEEE 802 address if desired.
capabilities are optionally provided which allow a multicast
Intermediate System to specify a "static" binding for a
subnetwork. One of the major purposes of providing a dynamic
is to customize a host's subnetwork address usage to the
of the attached systems. There is considerable differences in
numbers of group subnetwork addresses that a system can
using hardware hooks built into the integrated circuits used.
example the number of addresses that can be recognized by
may differ by an attached system depending upon the interface it
(e.g., Ethernet interface and FDDI within the same system may
quite different capabilities). Dynamic binding of this form is
in scope (members of a group may use different subnetwork
(e.g., IEEE 802 addresses) on different subnets).
Marlow [Page 40]
RFC 1768 CLNP Multicasting March 1995
Originating of Multicast
IP multicast originates multicast datagrams directly, where the
originating a datagram sends it with the group Subnetwork address
its destination. Hosts attached to the network where the datagram
originated receive the datagram directly
CLNP multicast originates multicast datagrams directly using
group's subnetwork address as its destination when multicast
mapping information is available. This case occurs when a
capable Intermediate System is attached to the subnetwork and a
on the subnetwork is announcing an interest in multicast
identified by a particular group Network address. The
Multicast IS may use MAM PDU mask parameters to provide
address mapping information for a large number of group
addresses. When there is no multicast address mapping information
the particular group Network address on a subnetwork with a
capable IS attached to it, hosts originate packets using
addresses sends to the "All Multicast Capable Intermediate Systems
SNPA address. This case occurs when there are no receivers of
multicast packets on the originating subnetwork. When a
capable Intermediate System is not attached to a subnetwork, the
System may utilize either preconfigured information (which might be
direct mapping from a portion of the group Network address) or
the "All Multicast Capable End Systems" address
Address Binding of Control
IP multicast sends the control packets related to the IGMP
on the same subnetwork address that is used by the multicast
traffic
CLNP multicast sends the control packets related to the ES-
protocol extensions on specific group subnetwork addresses (i.e.,
"All Multicast Capable End Systems" and "All Multicast Announcements
addresses).
Router Requirements for relaying Multicast
IP multicast requires that a multicast router run in "promiscuous
mode where it must receive all multicast datagrams originated on
subnetwork regardless of the destination. This is a result of
choices selected in the "Originating of Multicast Datagrams"
"Address Binding of Control Packets" discussed above
CLNP multicast allows a multicast router to limit multicast
reception to only those datagrams sent to the SNPA addresses
there is current multicast address mapping information or to the "
Marlow [Page 41]
RFC 1768 CLNP Multicasting March 1995
Multicast Capable Intermediate Systems" address. The intention is
allow the multicast routers to be in control of the SNPA
for multicast packets that they need to receive. This is a result
the choices selected in the "Originating of Multicast Datagrams"
"Address Binding of Control Packets" discussed above
Aggregation of Control
In IP multicast, a host is required to withhold an
report upon hearing another host reporting a similar interest in
particular Class D address on a particular subnetwork. This is
option for CLNP multicast (upon hearing interest in a
group Network address on a particular subnetwork). Such reports
not combined in IP multicast while CLNP multicast supports
multiple announcements (and address mappings) within a single packet
A mask feature for address mappings supports identifying mappings
a range of group Network addresses within a single control packet
Datagram Scope
IP multicast supports the use of the IP Hop Count as a means
support scope control. While not documented in RFC 1112, a
is also being used to use bits within the Class D address to
whether a datagram has single subnetwork, "campus" or global scope
CLNP has considerable scope control functionality. While the
Lifetime field can be employed in a similar way to the IP Hop Count
two additional options are available. The Radius scope
provides a mechanism for "administratively" setting distance
and de-couples the multicast scope control from the PDU
function. More importantly, the Prefix based scope control appears
provide considerable and flexible functionality that can adjust
situations where a known, hierarchical unicast addressing
exists
Marking of Multicast
IP multicast marks a multicast PDU via the use of an IP Class
address as its destination address parameter. CLNP multicast
both the PDU (a different PDU type) and the destination
(i.e., group Network address) parameter
Unicast Addressing
An IP address identifies a specific host interface while a
individual Network address (i.e., NSAP address) identifies
particular Network entity. This difference has lead to a
with RFC 1112. IP multicast requires a host which is attached
Marlow [Page 42]
RFC 1768 CLNP Multicasting March 1995
more than one subnetwork to originate a multicast packet on only
subnetwork. CLNP multicast requires a host which is attached to
than one subnetwork to originate a multicast packet on
subnetwork that the ISO ES-IS Configuration function is reporting
NSAP address contained in the source address parameter of
multicast PDU
Error
Error reports sent in response to receiving a multicast PDU are
permitted in IP multicast while they are permitted in CLNP multicast
Source
Source routing of multicast PDUs are permitted in IP multicast (
at the present time this is discouraged) while they are not
in CLNP multicast
Appendix B. Issues Under
This appendix is intended to record the current issues (as
at the March 1994 TUBA meeting).
1. Local versus Global address
The extensions to the ES-IS protocol provide a multicast
mapping function which supports dynamically binding a group
address to a subnetwork address. Concern has been expressed
this is an unnecessary feature which complicates the job of
administrators without suitable benefit. A static, global binding
group Network addresses to IEEE 802 subnetwork addresses, as is
by IP multicast has been suggested
The two main reasons that the group Network address to
(IEEE 802) address was made locally configurable were to
multicast on subnets with hosts having a mixture of capabilities (
to how many multicast subnetwork addresses a host could register
receive at a time) and to support multicast on subnets that do
use 48 bit IEEE 802 addresses. Thus it was felt that this should
done per subnetwork versus globally. Even multi-homed hosts
subnets that use 802 addresses may have varying capabilities (
at typical Ethernet, FDDI and 802.5 implementations).
One possible solution is to recommend a direct mapping in
Internet use of CLNP multicast on subnets which use IEEE 802
addressing. This could be a default for all Internet hosts.
policy would be needed to identify the Internet's group
address format. Given such a mapping the only operational
Marlow [Page 43]
RFC 1768 CLNP Multicasting March 1995
that would occur is that in the presence of a mapping server (
Active Multicast IS), which was supporting this mapping, a MAM
would periodically be sent with a Group Network Address Mask
would identify the direct mapping
2. "Real Time" Scope Control
The scope control features are provided via optional parameters.
of multicast transfer of audio and video streams may require
control mechanisms which operate very quickly
One possible solution is to embed scope control mechanisms into
group Network address itself. For example, a group Network
using the "Local" AFI is automatically limited to not cross inter
domain borders. Further, more flexible, address formats may
developed
[Deering91] Deering, S., "Multicast Routing in a
Internetwork", PhD thesis, Electrical Engineering Dept.,
University, December 1991.
[RFC1112] Deering, S., "Host Extensions for IP Multicasting",
STD 5, RFC 1112, Stanford University, August 1989.
[RFC1237] Colella, R., Gardner, E., and R. Callon, "Guidelines for
NSAP Allocation in the Internet", RFC 1237, NIST, Mitre, DEC,
1991.
[CLNP] Protocol for providing the connectionless-mode network service
International Standard 8473-1, Second Edition, ISO/IEC JTC 1,
Switzerland 1994. (Available via FTP
merit.edu:pub/iso/iso8473part1.ps).
[ES-IS] End system to Intermediate system routing exchange
for use in conjunction with the Protocol for providing
connectionless-mode network service, International Standard 9542,
ISO/IEC JTC 1, Switzerland 1987. (Available via FTP
merit.edu:pub/iso/iso9542.ps).
[MULT-AMDS]: Amendments to ISO standards to support CLNP
extensions
ISO 8348 AM5 Amendment to the Network Service to support Group
Addressing. International Standard ISO 8348 Amendment 5, ISO/IEC
1, Switzerland 1994.
Marlow [Page 44]
RFC 1768 CLNP Multicasting March 1995
ISO 8473-1 DAM1 - Draft Amendment to the Second Edition of
Protocol for providing the connectionless-mode network service [CLNP],
Multicast Extension, 1993.
ISO 9542 DAM2 - Draft Amendment to the ES-IS [ES-IS] protocol
Addition of connectionless- mode multicast capability, 1993.
Author's
Dave
Code B35
NSWC-
Dahlgren, VA. 22448
Phone: (703) 663-1675
EMail: dmarlow@relay.nswc.navy.
Marlow [Page 45]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
other technical nosh by ServerMasters Corporation
collaboration of BobX
