Network Working Group D. Farinacci Internet-Draft lispers.net Intended status: Experimental M. McBride Expires: 22 May 2023 Futurewei 18 November 2022 Group Address Allocation Protocol (GAAP) draft-farinacci-pim-gaap-00 Abstract This document describes a design for a lightweight decentralized multicast group address allocation protocol (named GAAP and pronounced "gap" as in "mind the gap"). The protocol requires no configuration setup and no centralized services. The protocol runs among group participants which need a unique group address to send and receive multicast packets. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 22 May 2023. Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. Farinacci & McBride Expires 22 May 2023 [Page 1] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3 3. Overview of Protocol Operation . . . . . . . . . . . . . . . 3 4. GAAP Message Format . . . . . . . . . . . . . . . . . . . . . 4 5. GAAP API . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. gaap.init() . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. gaap.allocate() . . . . . . . . . . . . . . . . . . . . . 6 5.3. gaap.release() . . . . . . . . . . . . . . . . . . . . . 6 6. Detail Protocol Operation . . . . . . . . . . . . . . . . . . 7 6.1. Allocating Group Addresses . . . . . . . . . . . . . . . 7 6.2. Claiming Group Addresses . . . . . . . . . . . . . . . . 8 6.3. Partition Repair . . . . . . . . . . . . . . . . . . . . 8 6.4. Releasing Group Addresses . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 10 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 10 Appendix B. Document Change Log . . . . . . . . . . . . . . . . 10 B.1. Changes to draft-farinacci-pim-gaap-00 . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction The Group Address Allocation Protocol (GAAP) is a decentralized multicast protocol used by participating applications which send and receive packets to/from a multicast group. The protocol is relatively lightweight, runs with minimized messaging and state so that it can run within a library a multicast application compiles into its executable binary. Other approaches to multicast group allocation have been proposed in the past, they include mDNS [RFC6762], MADCAP [RFC2730], MASC [RFC2909], and IPv6 Allocation Guidelines [RFC3307]. However, they require configuration, used on a single subnet, and are not decentralized. Farinacci & McBride Expires 22 May 2023 [Page 2] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 This document will describe the protocol operation, protocol message formats, the API definition, and how multicast applications use the API. 2. Definition of Terms Group Name: is an ASCII string used by applications so they can rendezvous on the same group address. The application is started using this group name parameter. Applications can use multiple group names if they have requirements to use multiple group addresses. Group Address: is a non-link-local IPv4 multicast group address [RFC1112] or an IPv6 multicast group address [RFC4291]. GAAP Group Address: is an IANA assigned non-link-local group address the GAAP protocol sends messages to. This address must not come from the GAAP multicast address block allocated by IANA. Hash Function: is a cryptographic hash function which takes the group name as input and produces a hash value as output. The GAAP protocol uses SHA-256 [RFC6234]. Hashed Value: is the output of a SHA-256 [RFC6234] hash function where the low order 32-bits are used to produce a unique network layer multicast group address. Achieving a unique 32-bits allows layer-2 switches to not have MAC multicast address collisions when mapped from multiple network layer multicast group addresses. Collided Group Address: a network layer group address where the low- order 32-bits of one group address is the same as the low-order 32-bits of another group address. It is desirable that the the low-order 32-bits of a mapped IPv6 group address to a MAC group address not be the same so layer-2 switches do not leak packets to non-group members. This is also true for IPv4 group addresses where the low-order 23-bits must be unique. Claim Message: a GAAP protocol message that allocates a unique group address and claims it among other GAAP nodes on the network. 3. Overview of Protocol Operation This section will describe the high-level functionality of the GAAP protocol. Each application runs the GAAP protocol by using the API defined in Section 5. * An application is started with a group name. Farinacci & McBride Expires 22 May 2023 [Page 3] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 * The group name is used to create a random allocated group address. * A timestamp is taken when the group address is created. * A Claim message, see Section 4, is sent with group name, group address, and timestamp to determine if the group address has been claimed by any other GAAP nodes. * If no Claim message is sent in response, the application can start using the group address. * If a Claim message is returned, a collision has occurred and the GAAP node must allocate another group address and send a Claim message for the new group address. * Claim messages are sent periodically. They are sent by a single node using a delay-timer suppression mechanism similar to IGMP [RFC1112]. See Section 6 for details. * GAAP nodes are not required to cache information from Claim messages. * GAAP is designed to be decentralized and stateless. The nodes that participate in the GAAP protocol are responsible for allocating and claiming group addresses. No other entities are needed. 4. GAAP Message Format At this time, there is a single message called the Claim message with type value 1. Type value of 0 is reserved. The Claim message is sent in a UDP checksummed packet where the source port is ephemeral and chosen by the sender and the destination port is a well-known port allocated by IANA. GAAP can work behind NAT and firewall devices as long as the GAAP destination port is permitted through filters. Farinacci & McBride Expires 22 May 2023 [Page 4] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Type=1 | Reserved | Record Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Multicast Group Address | \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | | R | IPv6 Multicast | e | Group Address | c | | o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ r | Timestamp | d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Group Name ... | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: GAAP Claim Message Packet field descriptions: Type=1: Claim Message Reserved: Set to 0 and ignored on receipt. Record Count: The number of records in this Claim message. Record field descriptions: IPv4 Multicast Group Address: a 32-bit multicast address in network byte order [RFC1112]. If all bits are set to 0, there is no IPv4 address being allocated and claimed. IPv6 Multicast Group Address: a 128-bit multicast address in network byte order [RFC4291]. If all bits are set to 0, there is no IPv6 address being allocated and claimed. Timestamp: Standard epoch UTC timestamp according to [RFC8536]. Group Name: A variable length group name the multicast application uses. It is in ASCII format [RFC0020]. The string is terminated with a null character. Farinacci & McBride Expires 22 May 2023 [Page 5] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 5. GAAP API The GAAP API has the following API calls a multicast application will use. A multicast application imports the library before using it in its code logic. This section documents a python library. 5.1. gaap.init() gapp.init() is used to initialize the GAAP API with a application callback function. The callback function is called when a group address has changed (due to collision) for a group name the application allocated. import gapp status = gapp.init(app_callback_func) if (status == False): print("error") exit(1) #endif def app_callback_func(group_name, group_address) print("Group name {} changed to group address {}". \ format((group_name, group_address)) #enddef 5.2. gaap.allocate() gaap.allocate() is used when the application needs a group address to send or receive on. import gapp group_name = "my-audio-group" group_address = gapp.allocate(group_name) if (group_address == None): print("error") exit(1) #endif print("Name {} allocated address {}".format(group_name, group_address)) 5.3. gaap.release() gaap.release() is used when an application is finished using a group address. Farinacci & McBride Expires 22 May 2023 [Page 6] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 import gapp group_address = gapp.allocate("my-audio-group") status = gapp.release(group_address) if (status == False): print("error") exit(1) #endif print("Released address {}".format(group_address)) 6. Detail Protocol Operation 6.1. Allocating Group Addresses When an application needs a group address it provides the GAAP API with a group name, the group name is used as input to a SHA-256 hash function [RFC6234]. Initially, when no group address collision is detected the group name is passed as a string to the hash function and the low-order 32-bits are used for a group address. The following pseudo-code illustrates the functionality: hash = sha256(group_name) low_bits = hash & 0xffffffff if (v4): group_address = 0xe0000000 | (low_bits & 0x007fffff) #endif if (v6): group_address = 0xff02...0000 | low_bits #endif return(group_address) When the hash function is used to resolve a collision, the following pseudo-code will illustrate how 3 more attempts are used to find a unique group address: for append in ["+1", "+2", "+3"]: hash = sha256(group_name + append) group_address = make_group_from_hash(hash) collision = send_claim(group_address) if (collision == False): return #endfor print("Collision limit reached") Farinacci & McBride Expires 22 May 2023 [Page 7] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 When a group address collision is detected by 2 GAAP nodes, the node with the earliest timestamp for the group address creation wins the collision and keeps using the address. The node with a later timestamp has the responsibility to allocate a new group address to prevent the collision. 6.2. Claiming Group Addresses When a group address is allocated by a GAAP node it will build and send a Claim message. Included in the Claim message is the group name, group address, and timestamp. If the group address collides with other GAAP nodes already using the address, one of the nodes will send a Claim message to notify the colliding node that it needs to allocate a new group address. A collision is defined to be the same group address allocated to 2 different group names. So if a GAAP node is claiming a group address for its group name and a Claim is received for this group name with the same group address, it is not a collision. It is simply a peer group participant claiming the group address you both agree to be using. Each GAAP node will periodically send Claim messages for all group names for the applications running on the node. It will do this in a multi-record Claim message. The periodic Claim message is sent by setting a rough 1 minute timer. The timer value is set to 1 minute plus a jitter value. The jitter value is a random number in a 10% range of 1 minute (60 to 66 seconds). When the timer expires, a Claim message is sent. Receivers of a Claim message who have their timer running, reset the timer and thereby suppresses sending their own Claim message. This allows only a single GAAP node that is using the group address to keep claiming the group is still in use. 6.3. Partition Repair There will be network outage situations where all GAAP nodes may not receive Claim messages. During a partition, duplicate group addresses may be allocated and used by nodes on each side of the partition. During this condition, multicast nodes can operate normally and there is no conflict until the partition heals. When the partition heals, duplicate group addresses will be detected and fixed. The group address with the earliest timestamp is used to determine who keeps the collided group address. All others will have to rehash a new group address and have the applications start using the new address (meaning senders will source using the new group address and receivers will leave the collided group and join the new group). Farinacci & McBride Expires 22 May 2023 [Page 8] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 6.4. Releasing Group Addresses When applications are no longer sending to a group address or not joined to a group address, they can inform the GAAP API to release the group. When this happens, the GAAP protocol stops claiming the group address in periodic messages and will not respond to a Claim for this address for a different group name. It is important for receiver applications to leave the group before releasing the group address. 7. Security Considerations There are no security considerations at this time. However, mechanisms are required to protect the GAAP group from being DoS attacked. And the privacy of Claim messages need to be maintained to circumvent man-in-the-middle eavesdropping attempts. This is work in progress. 8. IANA Considerations This document makes several requests for IANA. The first is to allocate a well-known UDP port number for the GAAP protocol. The second is to allocate IPv4 and IPv6 multicast addresses the GAAP protocol uses to send messages to. And the third is to allocate a multicast address block where GAAP allocated group addresses come from. 9. References 9.1. Normative References [RFC0020] Cerf, V. and RFC Publisher, "ASCII format for network interchange", STD 80, RFC 20, DOI 10.17487/RFC0020, October 1969, . [RFC1112] Deering, S. and RFC Publisher, "Host extensions for IP multicasting", STD 5, RFC 1112, DOI 10.17487/RFC1112, August 1989, . [RFC4291] Hinden, R., Deering, S., and RFC Publisher, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, . [RFC6234] Eastlake 3rd, D., Hansen, T., and RFC Publisher, "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI 10.17487/RFC6234, May 2011, . Farinacci & McBride Expires 22 May 2023 [Page 9] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 [RFC8536] Olson, A., Eggert, P., Murchison, K., and RFC Publisher, "The Time Zone Information Format (TZif)", RFC 8536, DOI 10.17487/RFC8536, February 2019, . 9.2. Informative References [RFC2730] Hanna, S., Patel, B., Shah, M., and RFC Publisher, "Multicast Address Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, DOI 10.17487/RFC2730, December 1999, . [RFC2909] Radoslavov, P., Estrin, D., Govindan, R., Handley, M., Kumar, S., Thaler, D., and RFC Publisher, "The Multicast Address-Set Claim (MASC) Protocol", RFC 2909, DOI 10.17487/RFC2909, September 2000, . [RFC3307] Haberman, B. and RFC Publisher, "Allocation Guidelines for IPv6 Multicast Addresses", RFC 3307, DOI 10.17487/RFC3307, August 2002, . [RFC6762] Cheshire, S., Krochmal, M., and RFC Publisher, "Multicast DNS", RFC 6762, DOI 10.17487/RFC6762, February 2013, . Appendix A. Acknowledgments The authors would like to thank the following people for their motivation to start this draft. They include Chris Hopps, Acee Lindem, David Lamparter, Jeff Tantsura, and Nate Karsens. Appendix B. Document Change Log B.1. Changes to draft-farinacci-pim-gaap-00 * Initial posting November 2022. Authors' Addresses Dino Farinacci lispers.net San Jose, CA United States of America Email: farinacci@gmail.com Farinacci & McBride Expires 22 May 2023 [Page 10] Internet-Draft Group Address Allocation Protocol (GAAP) November 2022 Mike McBride Futurewei Santa Clara, CA United States of America Email: mmcbride7@gmail.com Farinacci & McBride Expires 22 May 2023 [Page 11]