]> 5}="yes"?> Retired

Vancouver, British Columbia Canada deering@noreply.ietf.org

Futurewei Technologies USA

USA tte@cs.fau.de

PIM This memo specifies the extensions required of a host implementation of the Internet Protocol (IP) to support IP multicast with the IP service interface "Any Source Multicast" (ASM). This specification applies to both versions 4 and 6 of the Internet Protocol. Distribution of this memo is unlimited. This document replaces for everything but its specification of the IGMP version 1 protocol.

STATUS OF THIS MEMO This memo specifies the extensions required of a host implementation of the Internet Protocol (IP) to support IP multicast with the IP service interface "Any Source Multicast" (ASM). This specification applies to both versions 4 and 6 of the Internet Protocol. Distribution of this memo is unlimited. This document replaces for everything except for its specification of the IGMP version 1 protocol.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

INTRODUCTION

Summary This memo specifies the extensions required of a host implementation of the Internet Protocol (IP) to support IP multicast. It replaces for everything except for the specification of the protocol IGMP version 1 in Appendix I. of . This document declares including IGMP version 1 historic. specified IP multicast for version 4 of the IP protocol (IPv4, ), and refers to that version as IP. This document applies both to version 4 of the IP protocol and version 6 of the IP protocol (IPv6, ). The term IP is used in this document to refer to both versions. Where specifications in support of IP multicast for version 6 of the IP protocol where already provided by other RFCs, this document provides references to those pre-existing specifications, so that this document can serve as a complete single point of reference for the host extensions for IP multicast with either versions of IP. "Source Specific Multicast", (SSM, ) introduced a complementary extension to the IP service from the one specified here. It is relying on components specified here, such as {#ethernet}, and extending or superseding others. The service specified here is called "Any Source Multicast" (ASM) to distinguish it explicitly from SSM. This document also describes, where SSM changes specifications from . Due to the existence of both ASM and SSM, the term "IP multicast" best refers to the complete set of IP host extensions in support of either service options: this specification for ASM plus ). When the term IP multicast is used to refer to the IP multicast service without further qualification, then ASM is to be implied. This specification aims to maintain all the original text of where technically appropriate. This incurs the use of some historic language, such as "(internet) gateway" to refer to IP routers, and capitalization of chapter headings. See and for a detailed list of changes from .

Overview IP multicasting is the transmission of an IP datagram to a "host group", a set of zero or more hosts identified by a single IP destination address. A multicast datagram is delivered to all members of its destination host group with the same "best-efforts" reliability as regular unicast IP datagrams, i.e., the datagram is not guaranteed to arrive intact at all members of the destination group or in the same order relative to other datagrams. The membership of a host group is dynamic; that is, hosts may join and leave groups at any time. There is no restriction on the location or number of members in a host group. A host may be a member of more than one group at a time. A host need not be a member of a group to send datagrams to it. A host group may be permanent or transient. A permanent group has a 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 to transient groups which exist only as long as they have members. Internetwork forwarding of IP multicast datagrams is handled by "multicast routers" which may be co-resident with, or separate from, internet gateways. A host transmits an IP multicast datagram as a local network multicast which reaches all immediately-neighboring members of the destination host group. If the datagram has an IPv4 time-to-live or IPv6 hop limit greater than 1, the multicast router(s) attached to the local network take responsibility for forwarding it towards all other networks that have members of the destination group. On those other member networks that are reachable within the IPv4 time-to-live or IPv6 hop limit, an attached multicast router completes delivery by transmitting the datagram as a local multicast. This memo specifies the extensions required of a host IP implementation to support IP multicasting, where a "host" is any internet host or gateway other than those acting as multicast routers. The algorithms and protocols used within and between multicast routers are transparent to hosts and will be specified in separate documents. This memo also does not specify how local network multicasting is accomplished for all types of network, although it does specify the required service interface to an arbitrary local network and gives an Ethernet specification as an example. Specifications for other types of network will be the subject of future memos.

LEVELS OF CONFORMANCE There are three levels of conformance to this specification:

Level 0: no support for IP multicasting. There is, at this time, no requirement that all IP implementations support IP multicasting. Level 0 hosts will, in general, be unaffected by multicast activity. The only exception arises on some types of local network, where the presence of level 1 or 2 hosts may cause misdelivery of multicast IP datagrams to level 0 hosts. Such 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. Class D addresses in support of multicasting with IPv4 are described in section 4 of this memo, IPv6 addresses for IP multicasting are described in and .

Level 1: support for sending but not receiving multicast IP datagrams. Level 1 allows a host to partake of some multicast-based services, such as resource location or status reporting, but it does not allow a host to join any host groups. An IP implementation may be upgraded from level 0 to level 1 very easily and with little new code. Only sections 4, 5, and 6 of this memo are applicable to level 1 implementations.

Level 2: full support for IP multicasting. Level 2 allows a host to join and leave host groups, as well as send IP datagrams to host groups. Most IPv6 hosts require Level 2 support because IPv6 Neighbor Discovery (, as used on most link types), depends on multicast and requires that nodes join Solicited Node multicast addresses. Level 2 requires implementation of the Internet Group Management Protocol (IGMP) for IPv4 and the equivalent Multicast Listener Discovery Protocol (MLD) for IPv6 and extension of the IP and local network service interfaces within the host. The current protocol versions for full Level 2 support of IP multicasting are and or lightweight versions of either protocol . All of the following sections of this memo are applicable to level 2 implementations.

HOST GROUP ADDRESSES IPv4 Host groups are identified by class D IPv4 addresses, i.e., those with "1110" as their high-order four bits. Class E IPv4 addresses, i.e., those with "1111" as their high-order four bits, are reserved for future addressing modes. In Internet standard "dotted decimal" notation, IPv4 host group addresses range from 224.0.0.0 to 239.255.255.255. IPv4 host group addresses in the "Local Network Control Block", 224.0.0.0 - 224.0.0.255 are called Link-Local IPv4 host group addresses. IP datagrams with a Link-Local destination address are called Link-Local multicast packets. The IPv4 Link-Local addresses 224.0.0.0 is guaranteed not to be assigned to any group, and 224.0.0.1 is assigned to the permanent group of all IPv4 hosts (including gateways). This is used to address all IP multicast hosts on the directly connected network. There is no multicast address (or any other IP address) for all hosts on the total Internet. Allocation guidelines for Link-Local addresses are specified in . The addresses of well-known, permanent groups are to be published in "Assigned Numbers", see , currently through the IANA "IPv4 Multicast Address Space Registry". and refine more detailed allocation and uses of different sub-blocks of 224.0.0.0/4. The IPv6 all-hosts group address is FF02::1, IPv6 Host groups are identified by IPv6 addresses as defined in section 2.7 and updated by , . The addresses of other groups are currently published via the IANA "IPv6 Multicast Address Space Registry". IP addresses as specified in are not used for ASM IP multicast and are not considered IP host groups by . They are instead only the destination address part G of Source Specific Multicast (SSM) IP multicast (S,G) channels. Appendix I contains some background discussion of several issues related to host group addresses.

MODEL OF A HOST IP IMPLEMENTATION The multicast extensions to a host IP implementation are specified in terms of the layered model illustrated below in . In this model, ICMP/ICMPv6 and (for level 2 hosts) IGMP/MLD are considered to be implemented within the IP module, and the mapping of 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 be construed as constraining an actual implementation.

To provide level 1 multicasting, a host IP implementation MUST support the transmission of multicast IP datagrams. To provide level 2 multicasting, a host MUST also support the reception of multicast IP datagrams. Each of these two new services is described in a separate section, below. For each service, extensions are specified for the IP service interface, the IP module, the local network service interface, and an Ethernet local network module. Extensions to local network modules other than Ethernet are mentioned briefly, but are not specified in detail.

SENDING MULTICAST IP DATAGRAMS

Extensions to the IP Service Interface Multicast IP datagrams are sent using the same "Send IP" operation used to send unicast IP datagrams; an upper-layer protocol module merely specifies an IP host group address, rather than an individual IP address, as the destination. However, a number of extensions may be necessary or desirable. First, the service interface SHOULD provide a way for the upper-layer protocol to specify the IPv4 time-to-live or IPv6 hop limit of an outgoing multicast datagram, if such a capability does not already exist. If the upper-layer protocol chooses not to specify a time-to-live/hop limit, it SHOULD default to 1 for all multicast IP datagrams, so that an explicit choice is required to multicast beyond a single network. Second, for hosts that may be attached to more than one network, the service interface SHOULD provide a way for the upper-layer protocol to identify which network interface is be used for the multicast transmission. Only one interface is used for the initial transmission; multicast routers are responsible for forwarding to any other networks, if necessary. If the upper-layer protocol chooses not to identify an outgoing interface, a default interface SHOULD be used, preferably under the control of system management. Third (level 2 implementations only), for the case in which the host is itself a member of a group to which a datagram is being sent, the service interface SHOULD provide a way for the upper-layer protocol to inhibit local delivery of the datagram; by default, a copy of the datagram is looped back. This is a performance optimization for upper-layer protocols that restrict the membership of a group to one process per host (such as a routing protocol), or that handle loopback of group communication at a higher layer (such as a multicast transport protocol). IPv6 socket extensions supporting these functions are defined in , section 5.2.

Extensions to the IP Module To support the sending of multicast IP datagrams, the IP module MUST be extended to recognize IP host group addresses when routing outgoing datagrams. Most IP implementations include the following logic:

To allow multicast transmissions, the routing logic MUST be changed to:

If the sending host is itself a member of the destination group on the outgoing interface, a copy of the outgoing datagram MUST be looped-back for local delivery, unless inhibited by the sender. (Level 2 implementations only.) The IP source address of the outgoing datagram MUST be one of the individual addresses corresponding to the outgoing interface. A host group address or IP address from an SSM range MUST never be placed in the source address field or anywhere in a source route or record route option of an outgoing IP datagram. These packets are not IP multicast packets but simply invalid packets.

Extensions to the Local Network Service Interface No change to the local network service interface is required to support the sending of multicast IP datagrams. The IP module merely specifies an IP host group destination, rather than an individual IP destination, when it invokes the existing "Send Local" operation.

Extensions to an Ethernet Local Network Module The 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. An IPv4 host group address is mapped to an Ethernet multicast address by placing the low-order 23-bits of the IPv4 address into the low-order 23 bits of the Ethernet multicast address 01-00-5E-00-00-00 (hex). Because there are 28 significant bits in an IPv4 host group address, more than one host group address may map to the same Ethernet multicast address. Mapping of IPv6 host group addresses to Ethernet is defined in and . The address mappings for IP addresses do apply not only to IP host group addresses, but also to destination IP addresses used for SSM.

Extensions to Local Network Modules other than Ethernet Other networks that directly support multicasting, such as rings or buses conforming to the IEEE 802.2 standard, may be handled the same way as Ethernet for the purpose of sending multicast IP datagrams. For a network that supports broadcast but not multicast, such as the Experimental Ethernet, all IP host group addresses may be mapped to a single local broadcast address (at the cost of increased overhead on all local hosts). For a point-to-point link joining two hosts (or a host and a multicast router), multicasts SHOULD be transmitted exactly like unicasts. For a store-and-forward network like the ARPANET or a public X.25 network, all IP host group addresses might be mapped to the well-known local address of an IP multicast router; a router on such a network would take responsibility for completing multicast delivery within the network as well as among networks.

RECEIVING MULTICAST IP DATAGRAMS

Extensions to the IP Service Interface Incoming multicast IP datagrams are received by upper-layer protocol modules using the same "Receive IP" operation as normal, unicast datagrams. Selection of a destination upper-layer protocol is based on the protocol field in the IP header, regardless of the destination IP address. However, before any datagrams destined to a particular group can be received, an upper-layer protocol must ask the IP module to join that group. Thus, the IP service interface MUST be extended to provide two new operations:

The JoinHostGroup operation requests that this host become a member of the host group identified by "group-address" on the given network interface. The LeaveGroup operation requests that this host give up its membership in the host group identified by "group-address" on the given network interface. The interface argument may be omitted on hosts that support only one interface. For hosts that may be attached to more than one network, the upper-layer protocol may choose to leave the interface unspecified, in which case the request will apply to the default interface for sending multicast datagrams (see section 6.1). It is permissible to join the same group on more than one interface, in which case duplicate multicast datagrams may be received. It is also permissible for more than one upper-layer protocol to request membership in the same group. 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 does not belong to the given group on the given interface. LeaveHostGroup may succeed, but the membership persist, if more than one upper-layer protocol has requested membership in the same group. IPv6 socket extensions supporting these functions are defined in , section 5.2. specifies socket options for these functions for ASM and also includes socket options in support of SSM. Note that these are UDP socket extensions but not IP socket extensions due to the absence of widely adopted/required IP level socket APIs.

Extensions to the IP Module To support the reception of multicast IP datagrams, the IP module MUST be extended to maintain a list of host group memberships associated with each network interface. An incoming datagram destined to one of those groups is processed exactly the same way as datagrams destined to one of the host's individual addresses. Incoming datagrams destined to groups to which the host does not belong are discarded without generating any error report or log entry. On hosts with more than one network interface, if a datagram arrives via one interface, destined for a group to which the host belongs only on a different interface, the datagram MUST be quietly discarded. (These cases should occur only as a result of inadequate multicast address filtering in a local network module.) An incoming datagram is not rejected for having an IPv4 time-to-live of 1 or IPv6 Hop Limit of 1. This field MUST not automatically be decremented on arriving datagrams that are not being forwarded. An incoming datagram with an IP host group address in its source address field is quietly discarded. An ICMP/ICMPv6 error message (Destination Unreachable, Time Exceeded, Parameter Problem, Source Quench, or Redirect) is never generated in response to a datagram destined to an IP host group or SSM range destination IP address. The list of host group memberships is updated in response to JoinHostGroup and LeaveHostGroup requests from upper-layer protocols. Each membership should have an associated reference count or similar mechanism to handle multiple requests to join and leave the same group. On the first request to join and the last request to leave a group on a given interface, the local network module for that interface is notified, so that it may update its multicast reception filter (see section 7.3). When supporting Level 2, the IP module MUST also be extended to implement the IGMP protocol for IPv4 and the MLD protocol for IPv6 depending on the version(s) of IP to be supported. IGMP/MLD are used to keep neighboring multicast routers informed of the host group memberships present on a particular local network. See for potentially special treatment of the all-hosts groups in IGMP/MLD. Hosts and gateways MAY omit the sending of IGMP messages to report membership for Link-Local IPv4 host group addresses, especially on networks known not to (be able to) use any form of IGMP snooping. This does also apply for the IPv6 Link-Local host group all-hosts FF02::1, but not to other Link-Local IPv6 host groups. See .

Extensions to the Local Network Service Interface Incoming local network multicast packets are delivered to the IP module using the same "Receive Local" operation as local network unicast packets. To allow the IP module to tell the local network module which multicast packets to accept, the local network service interface is extended to provide two new operations:

where "group-address" is an IP host group address. The JoinLocalGroup operation requests the local network module to accept and deliver up subsequently arriving packets destined to the given IP host group address. The LeaveLocalGroup operation requests the local network module to stop delivering up packets destined to the given IP host group address. The local network module is expected to map the IP host group addresses to local network addresses as required to update its multicast reception filter. Any local 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 adequately. The local network module MUST NOT deliver up any multicast packets that were transmitted from that module; loopback of multicasts is handled at the IP layer or higher.

Extensions to an Ethernet Local Network Module To support the reception of multicast IP datagrams, an Ethernet module MUST be able to receive packets addressed to the Ethernet multicast addresses that correspond to the host's IP host group addresses. It is highly desirable to take advantage of any address filtering capabilities that the Ethernet hardware interface may have, so that the host receives only those packets that are destined to it. 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 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 reasons) to perform Ethernet address filtering within the software of the Ethernet module. This is not mandatory, however, because the IP module performs its own filtering based on IP destination addresses.

Extensions to Local Network Modules other than Ethernet Other multicast networks, such as IEEE 802.2 networks, can be handled the same way as Ethernet for the purpose of receiving multicast IP datagrams. For pure broadcast networks, such as the Experimental Ethernet, all incoming broadcast packets can be accepted and passed to the IP module for IP-level filtering. On point-to-point or store-and-forward networks, multicast IP datagrams will arrive as local network unicasts, so no change to the local network module should be necessary.

ROUTING MULTICAST IP DATAGRAMS IPv4 datagrams with a Link-Local destination address MUST never be forwarded to a different link by multicast routers, regardless of their time-to-live. See for explanations. The equivalent requirement are specified for IPv6 in , section 2.5.6. Rules for forwarding of non Link-Local IP multicast packets are outside the scope of this document.

Status changes

Moving RFC1112 and IGMPv1 to historic status This document moves to historic status which also moves the IGMP version 1 protocol as specified in Appendix 1 of to historic status, as it is not included into this document anymore. All other aspects of beside IGMPv1 are kept and updated by this document and maintain their current Internet Standard designation from through the normative status of this document.

Backward compatibility with IGMPv1 Current or future versions of IGMP or other protocols/mechanisms including but not necessary limited to , or do or may include backward compatibility with IGMPv1, such as in , which requires them to refer to the specification of IGMPv1. This document does not ask for any change to any specifications or implementations that includes any form of support for IGMPv1 for backward compatibility reasons as long as it also includes compatibility with a newer version of IGMP starting with . Any new or updated specification that wants to maintain such backward compatibility with IGMPv1 need to continue to reference as the specification of IGMPv1. Any future reference for new or updated work to any other definition from (host extensions for IP multicast and/or Any Source Multicast service) need to refer to this document instead of .

Update to RFC 791 This document is an update to because none of the core procedures to send and receive IP multicast packets described in this document match those defined for IP unicast packets in . Instead, IP multicast is carving out parts of the IP address space to trigger completely new forwarding for completely new entities: host groups in ASM, channels in SSM). See for further discussions.

Update to STD 5 This document replaces in which defines IPv4 () including its core extensions. Note: As there is no precedent for STD86 (IPv6) to include any specifications for extension of IPv6, this document is not asked to become part of STD86.

Changes from RFC1112 Beyond the status changes described in , this document introduces the following changes over . All requirements changes are intended to make this specification aligned with long-term, most widely implemented, deployed and standardised RFCs for IP multicast, so that this document does not create the need to change existing implementations or deployments, as could be the case if (without IGMPv1) was to be implemented today.

Normative language This document introduces the use of normative language through capitalization. preceded and hence did not include this language.

References to IGMPv1 References to IGMPv1 in are replaced with references to in this text.

New summary The new summarizes the scope of this document and the core new changes over .

Any-Source Multicast (ASM) This update introduces the term "ASM IP multicast" (ASM) as a new term for the IP service interface specified in this document (and previously in ) as explained in .

SSM explains the relationship of this document to SSM (). adds the specification that the term host groups specified in this document does not apply to destination addresses used for SSM. No functional changes to the IP multicast service are incurred by these changes, except that it acknowledges the existence of SSM which reduces the range of host group addresses used for ASM.

Applicability to both IPv4 and IPv6 This document is written to apply to both IPv4 and IPv6 by adding detail for IPv6 where only covered IPv4. This includes addressing and protocols in support of the service - Multicast Listener Discovery for IPv6 versus IGMP for IPv4. IPv6 documents such as and all its updates (e.g.: ) are defining the necessary wire encoding aspects of IP multicast in the assumption of the service of for IPv6, but without being able to refer to , as it was only defined for IPv4. Future documents can refer to this document as the IP multicast / ASM service for both IPv4 and IPv6. Additional text provides references for IETF UDP socket API specifications that instantiate the abstract APIs defined in this document. No functional changes to the IP multicast service are incurred by these changes.

IPv4 Local Network Control Block defines the requirement for IPv4 datagrams to the all-hosts group 224.0.0.1 to never be forwarded beyond a single network. In later RFCs, this behavior became the BCP for the whole IPv4 Local Network Control Block 224.0.0.0 - 224.0.0.255, making it the Link-Local host group address block for IPv4 multicast. and , section 4 are the BCPs covering this requirement. This document formalizes this BCP behavior as a standard requirement in , superseding and encompassing the more specific requirement for just 224.0.0.1 from , and mirroring the same standardized behavior for IPv6 Link-Local addresses. Because this is actually a requirement against IP multicast routers and not hosts, this is now also accordingly described in a separate section. This requirement does not incur changes over how IP multicast is implemented or deployed.

Special treatment of 224.0.0.1 and FF02::1 , section 7.2 introduced the requirements for hosts to permanently join 224.0.0.1. Its explains this requirement to be in support of IGMP (version 1). Likewise, , section 6. and , section 5. repeat this requirement, and , section 6. and section 6. also define the same requirement for the IPv6 all-hosts address FF02::1. Because this requirement is considered part of IGMP/MLD, and because this document does not anymore specify any form of IGMP, it does not repeat this requirement from . Instead, this requirement now solely relies on IGMP/MLD specifications to define it. These text changes do therefore not incur any requirements changes for implementations of these existing versions of IGMP/MLD, By leaving out this requirement from the document, future versions of IGMP/MLD are also free to choose whether to carry on this method without having to update this document. Note that omits this requirement.

IGMP/MLD messages for Link-Local IPv4 host group addresses , Appendix I. (IGMPv1), , , , require hosts to not send IGMP/MLD messages for the all-hosts group. This would be in conflict of the general rules of (outside of its IGMPv1 specific definitions) and equally this specification if it was not enhanced. This specification therefore contains new text that makes it compatible with existing IGMP/MLD specification, and with long tern established and deployed implementation practices. New text in explains how after , it became a common place implementation choice to not send IGMP messages for any IPv4 Link-Local host group address, and explains how this was done with good technical reason at the time. This behavior is so common, that mandates to explicit support it IGMP snooping implementations. Referring to that explanation, a new MAY requirement in allowing (but not recommending) this behavior makes existing specifications and deployments compatible with this documents specifications. It is only a MAY even though it is common in IPv4, because the experience with IPv6 shows that it does work (of course) equally well if this is not done, and can then support better MLD snooping than IGMP snooping.

Standard for IP multicasting in controlled networks This document removes the claim in the abstract of , that these host extensions are "... the recommended standard for IP multicasting in the Internet." The reason for this is that deprecated the ASM service across the Internet because there is no Internet Standard solution for protocols to support interdomain ASM except for , which is only applicable to IPv6, and even that solution does not resolve the challenges to source access control in interdomain deployments. In result, ASM is today "only" a recommended solution for controlled networks including controlled federated networks for applications for which SSM is not preferable. However, these limitations to the applicability of ASM do not impact the applicability of any parts of the host stack described in this document for other IP multicast service interfaces, specifically "Source Specific Multicast", , which inherits all aspects of ASM specified in this document, especially the sending (, ) of IP multicast packets as well as the mapping to ethernet (). It only amends the joining of IP multicast traffic on IP multicast receivers with additional procedures fitting into the host stack described in this document.

IANA Considerations

Protocol Numbers registry IANA is asked to replace the Reference field for the IGMP protocol in the Protocol Numbers registry (https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml) from to [THIS-RFC]. Explanation: This protocol number is used by all versions of IGMP, including and and is unaffected by making IGMP version 1 historic.

Internet Group Management Protocol (IGMP) Type Numbers Registry IANA is asked to replace the Reference to for the 0x11 / "IGMP Membership Query" entry in the "Internet Group Management Protocol (IGMP) Type Numbers Registry" (https://www.iana.org/assignments/igmp-type-numbers/igmp-type-numbers.xhtml) with ", [RFC2236], [RFC3376]". Explanation: This type code messages where introduced by but modified versions thereof where also introduced by [RFC2236] and [RFC3376], so that it is clearer if all three RFCs are indicated. All other references to in this registry are specifically referring to that RFC in it's role of defining IGMP version 1 and thus need to continue to refer to and not [THIS-RFC.

Multicast 48-bit MAC Addresses registry IANA is asked to replace the Reference field for the IPv4 Multicast range entry in the "IANA Multicast 48-bit MAC Addresses" (https://www.iana.org/assignments/ethernet-numbers) from to [THIS-RFC].

IPv4 Address range registries IANA is asked to replace the Reference field for the 240.0.0.0/4 entry in the "IANA IPv4 Special-Purpose Address Registry" (https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml) from to [THIS-RFC]. The Section 4 text stays unchanged. IANA is asked to replace the Reference to in the "IANA IPv4 Address Space Registry" (https://www.iana.org/assignments/ipv4-address-space/ipv4-address-space.xhtml) with [THIS-RFC].

IPv4 Multicast Address Space registry IANA is asked to replace the three references to in the "IPv4 Multicast Address Space Registry" (https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml) with [THIS-RFC].

IP Flow Information Export registry IANA is asked to replace the two references to in the "IPFIX Information Elements" registry (https://www.iana.org/assignments/ipfix/ipfix.xhtml) with [THIS-RFC].

This RFC proposes simple rules for broadcasting Internet datagrams on local networks that support broadcast, for addressing broadcasts, and for how gateways should handle them. This RFC suggests a proposed protocol for the ARPA-Internet community, and requests discussion and suggestions for improvements. We propose simple rules for broadcasting Internet datagrams on local networks that support broadcast, for addressing broadcasts, and for how gateways should handle them. This RFC suggests a proposed protocol for the ARPA-Internet community, and requests discussion and suggestions for improvements. This memo discusses the utility of "subnets" of Internet networks, which are logically visible sub-sections of a single Internet network. For administrative or technical reasons, many organizations have chosen to divide one Internet network into several subnets, instead of acquiring a set of Internet network numbers. This memo specifies procedures for the use of subnets. These procedures are for hosts (e.g., workstations). The procedures used in and between subnet gateways are not fully described. Important motivation and background information for a subnetting standard is provided in RFC-940. This RFC specifies a protocol for the ARPA-Internet community. If subnetting is implemented it is strongly recommended that these procedures be followed. This memo specifies the extensions required of a host implementation of the Internet Protocol (IP) to support multicasting. Recommended procedure for IP multicasting in the Internet. This RFC obsoletes RFCs 998 and 1054. [STANDARDS-TRACK] This memo documents IGMPv2, used by IP hosts to report their multicast group memberships to routers. It updates STD 5, RFC 1112. [STANDARDS-TRACK] This document specifies the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on Ethernet networks. It also specifies the content of the Source/Target Link-layer Address option used in Router Solicitation, Router Advertisement, Neighbor Solicitation, Neighbor Advertisement and Redirect messages when those messages are transmitted on an Ethernet. [STANDARDS-TRACK] This specification defines the addressing architecture of the IP Version 6 (IPv6) protocol. The document includes the IPv6 addressing model, text representations of IPv6 addresses, definition of IPv6 unicast addresses, anycast addresses, and multicast addresses, and an IPv6 node's required addresses. This document obsoletes RFC 3513, "IP Version 6 Addressing Architecture". [STANDARDS-TRACK] IP version 4 (IPv4) addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as source-specific multicast (SSM) destination addresses and are reserved for use by source-specific applications and protocols. For IP version 6 (IPv6), the address prefix FF3x::/32 is reserved for source-specific multicast use. This document defines an extension to the Internet network service that applies to datagrams sent to SSM addresses and defines the host and router requirements to support this extension. [STANDARDS-TRACK] Johns Hopkins University Applied Physics Lab IGMP is the protocol used by IPv4 systems to report their IP multicast group memberships to neighboring multicast routers. Version 3 of IGMP adds support for source filtering, that is, the ability for a system to report interest in receiving packets only from specific source addresses, or from all but specific source addresses, sent to a particular multicast address. That information may be used by multicast routing protocols to avoid delivering multicast packets from specific sources to networks where there are no interested receivers. This document specifies Version 3 of the Internet Group Management Protocol, IGMPv3. It is a revised version of the specification to include clarifications and fixes for errata in RFC 3376 and is backwards compatible with RFC 3376. This document updates RFC 2236 and obsoletes RFC 3376. Johns Hopkins University Applied Physics Lab This document updates RFC 2710, and it specifies Version 2 of the Multicast Listener Discovery Protocol (MLDv2). MLD is used by an IPv6 router to discover the presence of multicast listeners on directly attached links, and to discover which multicast addresses are of interest to those neighboring nodes. MLDv2 is designed to be interoperable with MLDv1. MLDv2 adds the ability for a node to report interest in listening to packets with a particular multicast address only from specific source addresses or from all sources except for specific source addresses. This document obsoletes RFC 3810. This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This memo specifies the Versatile Message Transaction Protocol (VMTP) [Version 0.7 of 19-Feb-88], a transport protocol specifically designed to support the transaction model of communication, as exemplified by remote procedure call (RPC). The full function of VMTP, including support for security, real-time, asynchronous message exchanges, streaming, multicast and idempotency, provides a rich selection to the VMTP user level. Subsettability allows the VMTP module for particular clients and servers to be specialized and simplified to the services actually required. Examples of such simple clients and servers include PROM network bootload programs, network boot servers, data sensors and simple controllers, to mention but a few examples. This RFC describes a protocol proposed as a standard for the Internet community. This document specifies an extension of the Routing Information Protocol (RIP), o expand the amount of useful information carried in RIP messages and to add a measure of security. This memo obsoletes RFC 1388, which specifies an update to the "Routing Information Protocol" STD 34, RFC 1058. [STANDARDS-TRACK] This document specifies version 6 of the Internet Protocol (IPv6), also sometimes referred to as IP Next Generation or IPng. [STANDARDS-TRACK] This document defines the "administratively scoped IPv4 multicast space" to be the range 239.0.0.0 to 239.255.255.255. In addition, it describes a simple set of semantics for the implementation of Administratively Scoped IP Multicast. Finally, it provides a mapping between the IPv6 multicast address classes [RFC1884] and IPv4 multicast address classes. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo documents version 2 of the OSPF protocol. OSPF is a link- state routing protocol. [STANDARDS-TRACK] This memo obsoletes RFC 1700 (STD 2) "Assigned Numbers", which contained an October 1994 snapshot of assigned Internet protocol parameters. This memo provides information for the Internet community. This document specifies the protocol used by an IPv6 router to discover the presence of multicast listeners (that is, nodes wishing to receive multicast packets) on its directly attached links, and to discover specifically which multicast addresses are of interest to those neighboring nodes. [STANDARDS-TRACK] The de facto standard Application Program Interface (API) for TCP/IP applications is the "sockets" interface. Although this API was developed for Unix in the early 1980s it has also been implemented on a wide variety of non-Unix systems. TCP/IP applications written using the sockets API have in the past enjoyed a high degree of portability and we would like the same portability with IPv6 applications. But changes are required to the sockets API to support IPv6 and this memo describes these changes. These include a new socket address structure to carry IPv6 addresses, new address conversion functions, and some new socket options. These extensions are designed to provide access to the basic IPv6 features required by TCP and UDP applications, including multicasting, while introducing a minimum of change into the system and providing complete compatibility for existing IPv4 applications. Additional extensions for advanced IPv6 features (raw sockets and access to the IPv6 extension headers) are defined in another document. This memo provides information for the Internet community. The Internet Group Management Protocol (IGMPv3) for IPv4 and the Multicast Listener Discovery (MLDv2) for IPv6 add the capability for applications to express source filters on multicast group memberships, which allows receiver applications to determine the set of senders (sources) from which to accept multicast traffic. This capability also simplifies support of one-to-many type multicast applications. This document specifies new socket options and functions to manage source filters for IP Multicast group memberships. It also defines the socket structures to provide input and output arguments to these new application program interfaces (APIs). These extensions are designed to provide access to the source filtering features, while introducing a minimum of change into the system and providing complete compatibility for existing multicast applications. This memo defines an address allocation policy in which the address of the Rendezvous Point (RP) is encoded in an IPv6 multicast group address. For Protocol Independent Multicast - Sparse Mode (PIM-SM), this can be seen as a specification of a group-to-RP mapping mechanism. This allows an easy deployment of scalable inter-domain multicast and simplifies the intra-domain multicast configuration as well. This memo updates the addressing format presented in RFC 3306. [STANDARDS-TRACK] This memo describes the recommendations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) snooping switches. These are based on best current practices for IGMPv2, with further considerations for IGMPv3- and MLDv2-snooping. Additional areas of relevance, such as link layer topology changes and Ethernet-specific encapsulation issues, are also considered. This memo provides information for the Internet community. This document specifies the Neighbor Discovery protocol for IP Version 6. IPv6 nodes on the same link use Neighbor Discovery to discover each other's presence, to determine each other's link-layer addresses, to find routers, and to maintain reachability information about the paths to active neighbors. [STANDARDS-TRACK] This document provides guidance for the Internet Assigned Numbers Authority (IANA) in assigning IPv4 multicast addresses. It obsoletes RFC 3171 and RFC 3138 and updates RFC 2780. This memo documents an Internet Best Current Practice. This document describes lightweight IGMPv3 and MLDv2 protocols (LW- IGMPv3 and LW-MLDv2), which simplify the standard (full) versions of IGMPv3 and MLDv2. The interoperability with the full versions and the previous versions of IGMP and MLD is also taken into account. [STANDARDS-TRACK] This specification defines an extension to the multicast addressing architecture of the IP Version 4 protocol. The extension presented in this document allows for unicast-prefix-based assignment of multicast addresses. By delegating multicast addresses at the same time as unicast prefixes, network operators will be able to identify their multicast addresses without needing to run an inter-domain allocation protocol. [STANDARDS-TRACK] When transmitting an IPv6 packet with a multicast destination address, the IPv6 destination address is mapped to an Ethernet link-layer multicast address. This document clarifies that a mapping of an IPv6 packet with a multicast destination address may in some circumstances map to an Ethernet link-layer unicast address. [STANDARDS-TRACK] This document updates the definitions of IPv6 multicast scopes and therefore updates RFCs 4007 and 4291. This document updates the IPv6 multicast addressing architecture by redefining the reserved bits as generic flag bits. The document also provides some clarifications related to the use of these flag bits. This document updates RFCs 3956, 3306, and 4291. This document recommends deprecation of the use of Any-Source Multicast (ASM) for interdomain multicast. It recommends the use of Source-Specific Multicast (SSM) for interdomain multicast applications and recommends that hosts and routers in these deployments fully support SSM. The recommendations in this document do not preclude the continued use of ASM within a single organization or domain and are especially easy to adopt in existing deployments of intradomain ASM using PIM Sparse Mode (PIM-SM).

HOST GROUP ADDRESS ISSUES This appendix is not part of the IP multicasting specification, but provides background discussion of several issues related to IP host group addresses.

Group Address Binding The binding of IP host group addresses to physical hosts may be considered a generalization of the binding of IP unicast addresses. An IP unicast address is statically bound to a single local network interface on a single 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. The multicast routers do not need to maintain a list of individual members of each host group. For example, a multicast router attached to an Ethernet need associate only a single Ethernet multicast address with each host group having local members, rather than a list of the members' individual IP or Ethernet addresses.

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 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 ) may generate higher- level transient "process 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. 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 users, perhaps generating new addresses until a suitably "quiet" one is found. In general, a host cannot assume that datagrams sent to any host group address will reach only the intended hosts, or that datagrams received as a member of a transient host group are intended for the recipient. Misdelivery must be detected at a level above IP, using higher-level identifiers or authentication tokens. Information transmitted to a host group address should be encrypted or governed by administrative routing controls if the sender is concerned about unwanted listeners.

Link-local IP multicast and IGMP/MLD On networks, where IP multicast packets are broadcast, such as (non-switched) ethernet, IP multicast packets will reach all level 2 IP multicast receivers without the need to use IGMP or MLD. This signaling is only necessary for IP multicast receivers when the sender is in a different LAN so that IP multicast routers can forward the IP multicast traffic from the sender network to the receiver network. IP multicast packet to a Link-Local IP multicast destination address do therefore technically never need any IGMP or MLD signaling on such (non-switched broadcast) networks, because they are never forwarded between networks (). During the early years of IPv4 multicast, this understanding resulted in implementations for protocols that receive Link-Local IPv4 multicast packet without implementing IGMP. Examples of such protocols include RIPv2 () or OSPF () and several other protocols, often running on IPv4 routers which had no IPv4 multicast routing implementation at the time and no IPv4 multicast applications for which they needed to be IPv4 multicast receiver for non Link-Local IPv4 multicast addresses. When these implementations later received implementations of level 2 IPv4 multicast support, those implementations excluded Link-Local host groups, so that those protocols would continue to run without IGMP as they had in before. Contributing to these implementation choices was also the fact that IGMP in the versions specified so far does not allow to keep track of ongoing receiver membership status in the absence of an IGMP router side implementation, called an IGMP querier. With the target (Link-Local IPv4 multicast only) protocols being deployed in the absence of any such IGMP querier, the use of IGMP could also serve arguably no purpose except for compliance with . This situation changed towards the end of the 1990th with the introduction of ethernet switches that snoop IGMP messages to constrain forwarding of IPv4 multicast packets for a particular IPv4 multicast group to only those ports with hosts joined to the group. This behavior was later documented in but was widely deployed even earlier due to the co-existence of ports with the different speeds 10Mbps, 100Mbps and 1Gbps, and the resulting need to protect the slower speed ports from potentially large rates of IPv4 multicast traffic between faster hosts. In result, IGMP snooping switches had to flood traffic to Link-Local IPv4 multicast groups due to the common absence of IGMP support for them, and this is accordingly also recommended by . Due to this long-term practice, this document is thus permitting this non-use of IGMP for Link-Local host groups by introducing a MAY for it in . Note that IP multicast routers do not and can not typically report IP multicast groups via IGMP or MLD, because they are not joined to them as an IP multicast host, but simply need to receive them as an IP multicast router to forward them. Even when an IP multicast router is joined to specific IP multicast group as an IP multicast host, reporting them via IGMP may sound futile because as an IP multicast router it would still need to receive the IP multicast traffic in the absence of such IGMP reporting, because it might need to forward it. However, this logic does not apply to Link-Local groups, because they are never forwarded and could thus be filtered by IGMP or MLD snooping switches if those switches could trust routers to report them correctly. Which they can not do for IPv4 due to its history. In recognition of this situation, for IPv6 did emphasize the need to report also Link-Local IPv6 group memberships to avoid these issues. Therefore this document also has no equivalent MAY statement for IPv6. Note that IGMP/MLD reporting for non Link-Local IP multicast groups from an IP multicast router joining it as a host is also not just a superficial specification requirement because of the assumption that routers need to receive all non Link-Local IP multicast packets. Switches that do support snooping of IP multicast routing protocols such as PIM may also be able to determine which traffic needs to be forwarded to an IP multicast router but those can may not include the groups that the IP multicast router has only joined to only as a host and is not reporting via IGMP/MLD.

Discussion and Explanations (TO BE REMOVED) [RFC-editor: Please remove this Appendix after observing the following section addressed to you] Please refer to for the non-process discussion of the goals of this document.

RFC-Editor notes The kramdown tooling did not allow to have references for both STD5 and RFC1112, those fail because the STD5 reference creates an "RFC1112" anchor. Thus there is no separate reference for RFC1112 in this version of the document. This needs to be fixed in XML by adding a full reference to RFC1112 and removing the RFC1112 anchor from the STD5 reference.

Goals and evolution of this document The initial goal of this document was to allow for IETF to declare the IGMPv1 protocol historic which today is a Full Internet Standard due to it being defined in RFC1112. This should be achieved without changing the Full Internet Standard status of the IP Host Extensions for IP Multicast and ASM IP Service interface specified in RFC1112 because those specification are as fundamental to the definition of IP multicast as RFC791 is for IP (unicast). The best way to achieve this seemed to be an update to RFC1112 which removes all of IGMPv1, but maintains the rest of the document. None of these removal of IGMPv1 changes changed the applicability or requirements to existing IP multicast (plus its protocols) implementations or other specifications. The next refinement was to rectify the situation that there is no specification explaining the same details as RFC1112 for IPv6 multicast even though RFC8200 (full internet standard) even explicitly includes IPv6 multicast, and a range of other RFC define necessary code-points (such as for ethernet mapping) for IPv6 multicast. Most of the text of this specification can hence can simply talk about "IP" which in this specification implies both IPv4 and IPv6, and only in places where IPv6 differs, does the document now include new explicit text, most often pointing to pre-existing RFCs specifying the necessary details for IPv6. Again, none of these changes impact other specs or deployments. The third step of refinement was add the necessary verbiage to explain the differences between SSM and the specifications in this document. None of these text enhancements incur any functional changes of long-term established practices. Instead, they are only resulting in references to SSM RFCs, introduction of the term ASM (which was previously only defined in SSM RFCs), and the limitation of applicability of terms in this document (such as host group) to their use with ASM. The last round of changes added and refined details to be in-line with long-term established practices and removing any possible contradictions between the original RFC1112 text and newer standards track specification such as IGMPv2/MLDv3 or long term established implementation practices. This includes the limitation of scope of ASM to controlled networks and the definition of the IPv4 Link-Local address range, which so far had only been defined through BCP RFC, unlike in IPv6, where it's part of the architecture, as well as permitting (but not recommending) non-use of IGMP for them. In summary, all changes in the document will make this document a replacement of rfc1112 which much more reflects the full internet standard nature of the technology than rfc1112 did as of recent.

Update to RFC791 This version of the text proposes that this spec is declared to be an update to RFC791. The argument made in to support this classification may not be persuasive enough (because the according rfc791 text may be read as a perfectly good extension point specification), in which case the update status and related text should be deleted. However, If anyone where to come up with a re-use of 224.0.0.0/4 for any non-IP multicast purposes, havoc might ensure with devices that do assume IP multicast semantics, so it may simply be prudent to include this declaration. It would also make the relationship between IPv4 and IPv4 multicast be more aligned with IPv6, where IPv6 multicast is included in RFC8200.

Changelog This document is hosted at https://github.com/toerless/rfc1112bis. Please submit issues with this text as issues to that github and report them on pim@ietf.org.

draft-ietf-pim-rfc1112bis-03 Changed document text to make the term "ASM" apply only to the IP service interface (extensions) specified by the document (and shown and explained in existing text), instead of the whole host extensions specified in this document (as it was written up to up to -02). This is the only correct semantic, given how all the host exensions specified in this document are shared by SSM, only the IP service interface is changed/amended by SSM. Subdivided section 2 (INTRODUCTION) into sections 2.1 (Summary), which contains new text from this spec, and 2.2 (Overview), which is unchanged RFC1112 text. Newly written section 2.1 to summarize the key content of this document. This was so far only explained in the much later changes from rfc1112 section. Includes IPv4/IPv6 applicability, ASM/SSM naming and maintaining most of RFC1112 text as a goal. Introduced text to define and explain link local IPv4 host group addresses 224.0.0.0 - 224.0.0.255. This was triggered by trying to fix the rfc1112 text sections that Brian Haberman was concerned about, which did cover behavior for 224.0.0.1. As it turns out, the behavior for 224.0.0.1 was quickly adopted by other protocols getting 224.0.0.0/24 addresses and there has been no functional specification to explain the non-forwarding behavior for these link-local addresses. Instead, only IANA allocation guideline RFCs where introducing them. This is now rectified with new explanatory text in this spec. and a new MAY requirement to permit non-use of IGMP for those groups. See . Changed references to IGMPv3 and MLDv2 to the -bis drafts currently in RFC-editor queue. Also triggered by Brian Haberman mentioning them. Improved wording in "(Normative) Status Change" section 9. 5.1 Removed "Update to rfc791" as an open issue and instead claimed it as fact in section 9.3. Added discussion about this point to the discussion appendix that is to be removed by RFC-editor. 5.1 Also added subsection to declare that this document replaces RFC1112 in STD5. Enhanced/New text in section 10., "changes from RFC1112" Especially explaining the changes in the normative section explained above and below, triggered by Brian's review. Applying changes proposed by Brian Haberman during WGLC. 7.1 Changed meaning of IP from "IPv4" to "IPv4 and IPv6", accordingly updated all text. Makes a lot of sense given the goal of showing how most of the IP multicast host stack operates the same for IPv4 and IPv6. 7.2 Re-added requirement for routers not to forward link-local multicast 7.3 adding MAY requirement to allow non-signaling of Link-Local scope IPv4 multicast and IPv6 all-hosts group, and explanations how this is better than the prior definitions from rfc1112. Also includes new (length) Appendix A.3 to justify this for IPv4. 7.4 text nits (thanks, Brian).

draft-ietf-pim-rfc1112bis-02 Removed unused references, fefresh - waiting for more reviews. Added IANA section for updates from RFC1112 to RFC1112bis. Added references to RFC5771 and RFC6034 because they actually are the references for the IANA 224.0.0.0/4 registrations, which seems a bit undocumented given how RFC1112 did introduce the definition (before IANA).

draft-ietf-pim-rfc1112bis-01 Fix up reference for IGMPv3. Refined candidate open issues. Removed author discussion.

draft-eckert-pim-rfc1112bis-02 Changed core references from numbered style to name style . Changed copyright clause to pre5378Trust200902, which is the same as used for RFC8200 due to the presence of text with similar early status. To resolve Dino's concerns at IETF116 with -01: Added hopefully extensive explanation wrt. to how to treat IGMPv1 based on Dino's feedback from IETF117: This document does not ask for any removal of IGMPv1 in any IETF specs which include it for backward compatibility reasons, it only effectively causes it to become historic once RFC1112 would be declared historic. To resolve Alvaros concerns at IETF1116 with -01: Added normative language (MUST/SHOULD). Seems as if this is quite easy given how "must" was written appropriately in the original text. The logic of applying MUST/MUST-NOT was based on understanding by the author how none of the MUST would actually put existing working implementations out of compliance. Added explicit text to move rfc1112 to historic status. Moved explanation of changes from rfc1112 from appendix to main text as this seem to the common practice for document updates. Added claim for this document to be an update to rfc791. See open issues section though.

draft-ietf-pim-rfc1112bis-00 Just changed title, added github pointer.

draft-eckert-pim-rfc1112bis-01 Changed all use of IPv4 back to IP. Seems standard in IETF specs. Only IPv6 has in IETF specs the distinction of including the version. Changed Steve Deerings address to a pseudo-email address at IETF. See prior section. Converted document into kramdownrfc2629 format for easier editing. Claims that rfc2119 language is not desired/used (to maintain maximum original text without changes). Rewrote section for updates to rfc1112 to hopefully better motivate/explain the reason for this document and detail what its changes are.

draft-eckert-pim-rfc1112bis-00 Initial version based on text version, edited.