Internet DRAFT - draft-karstens-pim-zeroconf-mcast-addr-alloc-ps
draft-karstens-pim-zeroconf-mcast-addr-alloc-ps
Network Working Group N. Karstens
Internet-Draft Garmin International
Intended status: Standards Track D. Farinacci
Expires: 29 January 2024 lispers.net
M. McBride
Futurewei
28 July 2023
Zeroconf Multicast Address Allocation Problem Statement and Requirements
draft-karstens-pim-zeroconf-mcast-addr-alloc-ps-01
Abstract
This document describes a network that requires unique multicast
addresses to distribute data. Various challenges are discussed, such
as the use of multicast snooping to ensure efficient use of
bandwidth, limitations of switch hardware, problems associated with
address collisions, and the need to avoid user configuration. After
all limitations were considered it was determined that multicast
addresses need to be dynamically-assigned by a decentralized, zero-
configuration protocol.
Requirements and recommendations for suitable protocols are listed
and specific considerations for assigning IPv4 and IPv6 addresses are
reviewed. The document closes with several solutions that are
precluded from consideration.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 29 January 2024.
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Address Collisions . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 4
4. IPv6 Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. IPv4 Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Excluded Solutions . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Marine networks contain a combination of sensors, controls, and
displays. Installations vary widely depending on the design and
intended purpose of the boat and the amount of redundancy required.
Sensors on these networks can be a mix of low-cost, low-bandwidth
devices, like temperature or fluid sensors, and high-bandwidth
devices, like radar, sonar, and video cameras. In most cases, these
networks use a single subnet and therefore require layer-2 switches
to be deployed.
The most optimal way to distribute sensor data to all displays on the
network is multicast. However, use of traditional switches can be
problematic when both high-bandwidth and low-bandwidth devices are
installed. Low-bandwidth devices are commonly designed with a low-
speed link to reduce cost, and the multicast stream from the high-
bandwidth device can overwhelm this link. Switch hardware at the low
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price points that are acceptable to the market do not support source-
specific multicast. Instead, multicast streams are differentiated by
destination address and switches with multicast snooping [RFC4541] in
a default-block configuration are used to isolate multicast streams
to the ports with devices that request the data.
This technique presents several challenges. First, defining an
industry-standard set of pre-allocated addresses is not practical due
to the wide variety of network designs. Manually configuring
addresses for each device is not a user-friendly solution. MADCAP
[RFC2730] could be used to dynamically assign addresses, but its
reliance on a dedicated server results in a single point of failure
for the system, which is not acceptable for the target environment.
Finally, this method is susceptible to link-layer address collisions
(see Section 2 for further discussion).
The desired solution needs to be a decentralized, zero-configuration
protocol for dynamically assigning multicast addresses. This
document serves as a basis for developing suitable protocols by
defining the problem, discussing constraints, and listing
requirements.
1.1. 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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Address Collisions
Link-layer address collisions are a concern in two cases.
First, many Ethernet chips include the ability to filter out unwanted
traffic. This is typically configured by the network stack in
response to an application joining a multicast group. Any link-layer
address collision would require that the network stack use CPU time
to filter out traffic by its IPv6 multicast address, which may cause
poor performance.
Networks that use multicast snooping switches are also susceptible to
address collisions. According to Section 4 of [RFC4541], most switch
vendors forward multicast traffic based only on the link-layer
address (see the results for Q2 and Q3). This means that unwanted
data will be transmitted over the link and, depending on the nature
of the data, may result in a low-bandwidth link being saturated by a
high-bandwidth stream.
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3. Protocol Requirements
A decentralized, zero-configuration protocol for dynamic multicast
address assignment MUST have the following characteristics:
1. Does not rely on a single point of failure
2. Does not depend on user configuration
3. Coexists with other multicast address assignment protocols
4. Supports operation on a single subnet
5. Does not require an Internet connection
6. Supports multiple applications on the same host
7. Detects and resolves address collisions
Note that an extreme case of address collision may occur after a
network partition, when intermittent link failure temporarily divides
the network into multiple segments.
A protocol SHOULD ideally have the following characteristics:
1. Supports operation across multiple subnets
2. Does not require significant changes to existing standards
3. Uses functionality commonly available on a variety of platforms
4. Uses capabilities commonly provided to unprivileged applications
5. Avoids depending on configuration data loaded during device
manufacture
6. Minimizes network traffic
4. IPv6 Considerations
The IPv6 multicast address guidelines specified in [RFC3307] are
well-structured and robust. Section 2 defines the lower 32 bits of
the IPv6 address, which are mapped directly to the link-layer, as the
group ID, and then assigns ranges of group ID values based on how
they are allocated. Section 4.3 describes dynamic assignment of
group ID values and lists two different approaches (server allocation
and host allocation). However, both approaches are assigned the same
range of group ID values, which means they cannot coexist without
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risking an address collision. Also concerning is that the range for
dynamic assignment overlaps with the range used for solicited-node
multicast addresses (see Section 2.7.1 of [RFC4291]).
5. IPv4 Considerations
Section 6.4 of [RFC1112] recognizes that more than one IPv4 multicast
address can be mapped to the same Ethernet multicast address. This
is because the lowest 23 bits are mapped to the Ethernet multicast
address. A 32-bit IPv4 multicast address has a 4-bit prefix, which
leaves 5 bits inconsequential to the operation, or 32 addresses.
The guidelines for allocating IPv4 multicast addresses in [RFC5771]
did not anticipate a need to avoid address collisions. As such, the
recommendation for all new designs using dynamic assignment is to use
IPv6. If this is not feasible, then the recommendation is for the
protocol to assign addresses from a suitable range in the
Administratively Scoped Block (239.0.0.0/8) and be aware of other
applications on the network using addresses it may collide with.
6. Excluded Solutions
The prefix for IPv4 and IPv6 multicast messages being transmitted on
Ethernet are specified in [RFC1112], Section 6.4 and [RFC2464],
Section 7, respectively. Allowing a different prefix would support
at least two solutions that are being excluded from consideration.
First, reducing the size of the prefix would increase the size of the
group ID, thereby reducing the probability of an address collision.
Because link-layer addresses are only relevant on the local subnet,
it would also be possible to develop a new protocol to dynamically
map network-layer multicast addresses to link-layer multicast
addresses in an operation somewhat analogous to DHCP. Multicast
packets routed from outside the network could have the address mapped
at ingress without any assignment protocol.
Ultimately, using a different prefix seemed like a significant change
that would only gain widespread platform support after significant
delay.
With IPv4, reserving 32 separate address ranges in the registry could
prevent address collisions. However, [RFC5771] cautions that IPv4
multicast address space is limited and this approach seemed
excessive.
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7. Security Considerations
Security considerations will be discussed by any proposed zero-
configuration multicast address allocation algorithm.
8. IANA Considerations
This document has no IANA actions.
9. Acknowledgement
Special thanks to the National Marine Electronics Association for
their contributions in developing marine industry standards and their
support for this research.
Thanks also to the members of the PIM working group for their early
brainstorming sessions and review of this draft.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
Addresses", RFC 3307, DOI 10.17487/RFC3307, August 2002,
<https://www.rfc-editor.org/info/rfc3307>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, DOI 10.17487/RFC1112, August 1989,
<https://www.rfc-editor.org/info/rfc1112>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
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[RFC2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address
Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
DOI 10.17487/RFC2730, December 1999,
<https://www.rfc-editor.org/info/rfc2730>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
[RFC5771] Cotton, M., Vegoda, L., and D. Meyer, "IANA Guidelines for
IPv4 Multicast Address Assignments", BCP 51, RFC 5771,
DOI 10.17487/RFC5771, March 2010,
<https://www.rfc-editor.org/info/rfc5771>.
Authors' Addresses
Nate Karstens
Garmin International
Email: nate.karstens@gmail.com
Dino Farinacci
lispers.net
Email: farinacci@gmail.com
Mike McBride
Futurewei
Email: michael.mcbride@futurewei.com
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