v6ops J. Brzozowski
Internet-Draft Comcast Cable
Intended status: Best Current Practice G. Van De Velde
Expires: February 1, 2018 Nokia
July 31, 2017

Unique IPv6 Prefix Per Host


In some IPv6 environments, the need has arisen for hosts to be able to utilize a unique IPv6 prefix, even though the link or media may be shared. Typically hosts (subscribers) on a shared network, either wired or wireless, such as Ethernet, WiFi, etc., will acquire unique IPv6 addresses from a common IPv6 prefix that is allocated or assigned for use on a specific link.

In most deployments today, IPv6 address assignment from a single IPv6 prefix on a shared network is done by either using IPv6 stateless address auto-configuration (SLAAC) and/or stateful DHCPv6. While this is still viable and operates as designed, there are some large scale environments where this concept introduces significant performance challenges and implications, specifically related to IPv6 router and neighbor discovery.

This document outlines an approach utilising existing IPv6 protocols to allow hosts to be assigned a unique IPv6 prefix (instead of a unique IPv6 address from a shared IPv6 prefix). Benefits of unique IPv6 prefix over a unique IPv6 address from the service provider include improved subscriber isolation and enhanced subscriber management.

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 http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on February 1, 2018.

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Table of Contents

1. Introduction

The concepts in this document are originally developed as part of a large scale, production deployment of IPv6 support for a provider managed shared network service. In this document IPv6 support does not preclude support for IPv4; however, the primary objectives for this work was to make it so that user equipment (UE) were capable of an IPv6 only experience from a network operators perspective. In the context of this document, UE can be 'regular' end-user-equipment, as well as a server in a datacenter, assuming a shared network (wired or wireless).

Details of IPv4 support are out of scope for this document. This document will also, in general, outline the requirements that must be satisfied by UE to allow for an IPv6 only experience.

In most current deployments, User Equipment (UE) IPv6 address assignment is commonly done using either IPv6 SLAAC RFC4862 and/or DHCP IA_NA RFC3315. During the time when this approach was developed and subsequently deployed, it has been observed that some operating systems do not support the use of DHCPv6 for the acquisition of IA_NA per RFC7934. As such the use of IPv6 SLAAC based subscriber and address management for provider managed shared network services is the recommended technology of choice, as it does not exclude any known IPv6 implementation. In addition an IA_NA-only network is not recommended per RFC 7934 RFC7934 section 8. This document will detail the mechanics involved for IPv6 SLAAC based address and subscriber management coupled with stateless DHCPv6, where beneficial.

This document will focus upon the process for UEs to obtain a unique IPv6 prefix.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

2. Motivation and Scope of Applicability

The motivation for this work falls into the following categories:

3. Design Principles

The First Hop router discussed in this document is the L3-Edge router responsible for the communication with the devices (hosts and subscribers) directly connected to a provider managed shared network, and to transport traffic between the directly connected devices and between directly connected devices and remote devices.

The work detailed in this document is focused on providing details regarding best common practices of the IPv6 neighbor discovery and related IPv6 address management settings between the First Hop router and directly connected hosts/subscribers. The documented Best Current Practice helps a service provider to better manage the shared provider managed network on behalf of the connected devices.

The Best Current Practice documented in this note is to provide a unique IPv6 prefix to hosts/subscribers devices connected to the provider managed shared network. Each unique IPv6 prefix can function as control-plane anchor point to make sure that each subscriber is receiving expected subscriber policy and service levels (throughput, QoS, security, parental-control, subscriber mobility management, etc.).

4. IPv6 Unique Prefix Assignment

When a UE connects to the shared provider managed network and is attached, it will initiate IP configuration phase. During this phase the UE will, from an IPv6 perspective, attempt to learn the default IPv6 gateway, the IPv6 prefix information, the DNS information RFC8106, and the remaining information required to establish globally routable IPv6 connectivity. For that purpose, the the UE/subscriber sends a RS (Router Solicitation) message.

The First Hop Router receives this UE/subscriber RS message and starts the process to compose the response to the UE/subscriber originated RS message. The First Hop Provider Router will answer using a unicast RA (Router Advertisement) to the UE/subscriber. This RA contains two important parameters for the EU/subscriber to consume: a Unique IPv6 prefix (currently a /64 prefix) and some flags. The Unique IPv6 prefix can be derived from a locally managed pool or aggregate IPv6 block assigned to the First Hop Provider Router or from a centrally allocated pool. The flags indicate to the UE/subscriber to use SLAAC and/or DHCPv6 for address assignment; it may indicate if the autoconfigured address is on/off-link and if 'Other' information (e.g. DNS server address) needs to be requested.

The IPv6 RA flags used for best common practice in IPv6 SLAAC based Provider managed shared networks are:

The use of a unique IPv6 prefix per UE adds an additional level of protection and efficiency as it relates to how IPv6 Neighbor Discovery and Router Discovery processing. Since the UE has a unique IPv6 prefix all traffic by default will be directed to the First Hop provider router. Further, the flag combinations documented above maximise the IPv6 configurations that are available by hosts including the use of privacy IPv6 addressing.

The architected result of designing the RA as documented above is that each UE/subscriber gets its own unique IPv6 prefix for which it can use SLAAC or any other method to select its /128 unique address. In addition it will use stateless DHCPv6 to get the IPv6 address of the DNS server, however it SHOULD NOT use stateful DHCPv6 to receive a service provider managed IPv6 address. If the UE/subscriber desires to send anything external including other UE/subscriber devices (assuming device to device communications is enabled and supported), then, due to the L-bit set, it SHOULD send this traffic to the First Hop Provider Router.

After the UE/subscriber received the RA, and the associated flags, it will assign itself a 128 bit IPv6 address using SLAAC. Since the address is composed by the UE/subscriber device itself, it will need to verify that the address is unique on the shared network. The UE/subscriber will for that purpose, perform Duplicate Address Detection algorithm. This will occur for each address the UE attempts to utilize on the shared provider managed network.

5. IPv6 Neighbor Discovery Best Practices

An operational consideration when using IPv6 address assignment using IPv6 SLAAC is that after the onboarding procedure, the UE/subscriber will have a prefix with certain preferred and valid lifetimes. The First Hop Provider Router extends these lifetimes by sending an unsolicited RA, the applicable MaxRtrAdvInterval on the first hop router MUST therefore be lower than the preferred lifetime. One consequence of this process is that the First Hop Router never knows when a UE/subscriber stops using addresses from a prefix and additional procedures are required to help the First Hop Router to gain this information. When using stateful DHCPv6 IA_NA for IPv6 UE/subscriber address assignment, this uncertainty on the First Hop Router is not of impact due to the stateful nature of DHCPv6 IA_NA address assignment.

Following is a reference table of the key IPv6 router discovery and neighbor discovery timers for provider managed shared networks:

The stateless nature of the UE/subscriber IPv6 SLAAC connectivity model provides a consideration to make regarding resource consumption (i.e. memory, neighbor state) on the First Hop Router. To reduce undesired resource consumption on the First Hop Router the desire is to remove UE/subscriber context in the case of non-permanent UE, such as in the case of WiFi hotspots as quickly as possible. A possible solution is to use a subscriber inactivity timer which, after tracking a pre-defined (currently unspecified) number of minutes, deletes the subscriber context on the First Hop Router.

When employing stateless IPv6 address assignment, a number of widely deployed operating systems will attempt to utilise RFC 4941 RFC4941 temporary 'private' addresses.

Similarly, when using this technology in a datacenter, the UE server may need to use several addresses from the same Unique IPv6 Prefix, for example because is using multiple virtual hosts, containers, etc. in the bridged virtual switch. This can lead to the consequence that a UE has multiple /128 addresses from the same IPv6 prefix. The First Hop Provider Router MUST be able to handle the presence and use of multiple globally routable IPv6 addresses.

For accounting purposes, the First Hop Provider Router must be able to send usage statistics per UE/subscriber using Radius attributes.

6. IANA Considerations

No IANA considerations are defined at this time.

7. Security Considerations

The mechanics of IPv6 privacy extensions RFC4941 is compatible with assignment of an Unique IPv6 Prefix per Host. The combination of both IPv6 privacy extensions and operator based assignment of a Unique IPv6 Prefix per Host provides each implementing operator a tool to manage and provide subscriber services and hence reduces the experienced privacy within each operator controlled domain. However, beyond the operator controlled domain, IPv6 privacy extensions provide the desired privacy as documented in RFC4941.

No other additional security considerations are made in this document.

8. Acknowledgements

The authors would like to thank the following, in alphabetical order, for their contributions:

Brian Carpenter, Tim Chown, Lorenzo Colitti, Killian Desmedt, Brad Hilgenfeld, Wim Henderickx, Erik Kline, Warren Kumari, Thomas Lynn, Jordi Palet, Phil Sanderson, Colleen Szymanik, Jinmei Tatuya, Eric Vyncke, Sanjay Wadhwa

9. 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.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 2003.
[RFC4861] Narten, T., Nordmark, E., Simpson, W. and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007.
[RFC4862] Thomson, S., Narten, T. and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007.
[RFC4941] Narten, T., Draves, R. and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007.
[RFC7934] Colitti, L., Cerf, V., Cheshire, S. and D. Schinazi, "Host Address Availability Recommendations", BCP 204, RFC 7934, DOI 10.17487/RFC7934, July 2016.
[RFC8106] Jeong, J., Park, S., Beloeil, L. and S. Madanapalli, "IPv6 Router Advertisement Options for DNS Configuration", RFC 8106, DOI 10.17487/RFC8106, March 2017.

Authors' Addresses

John Jason Brzozowski Comcast Cable 1701 John F. Kennedy Blvd. Philadelphia, PA USA EMail: john_brzozowski@cable.comcast.com
Gunter Van De Velde Nokia Antwerp Belgium EMail: gunter.van_de_velde@nokia.com