v6ops J. Brzozowski
Internet-Draft Comcast Cable
Intended status: Best Current Practice G. Van De Velde
Expires: November 11, 2016 Nokia
May 10, 2016
Unique IPv6 Prefix Per Host
draft-ietf-v6ops-unique-ipv6-prefix-per-host-01
Abstract
In some IPv6 environments the need has arisen for hosts to be able to
utilise a unique IPv6 prefix even though the link or media may be
shared. Typically hosts (subscribers) on a shared network, like Wi-
Fi or Ethernet, will acquire unique IPv6 addresses from a common IPv6
prefix that is allocated or assigned for use on a specific link.
Benefits of a unique IPv6 prefix compared to a unique IPv6 address
from the service provider are going from enhanced subscriber
management to improved isolation between subscribers.
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).
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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Drafts is at http://datatracker.ietf.org/drafts/current/.
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 November 11, 2016.
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Copyright Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Motivation and Scope of Applicability . . . . . . . . . . . . 3
3. Design Princinples . . . . . . . . . . . . . . . . . . . . . 3
4. IPv6 Unique Prefix Assignment . . . . . . . . . . . . . . . . 4
5. IPv6 Neighbourship Discovery Best Practices . . . . . . . . . 5
6. Future work . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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.
Details of IPv4 support are out of scope for this document. This
document will also, in general, outline the requirements that must be
satified by UE to allow for an IPv6 only experience.
In most deployments today User Equipment (UE) IPv6 address assignment
is commonly done using either IPv6 SLAAC RFC4862 [RFC4862] and/or
DHCP IA_NA RFC3315 [RFC3315]. However, at current time there is a
non-trivial UE/subscriber base not supporting DHCPv6 IA_NA, making
IPv6 SLAAC based subscriber and address management for provider
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managed shared network services the technology of choice as it does
not exclude any known IPv6 implementation. 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.
2. Motivation and Scope of Applicability
The motivation for this work falls into the following categories:
o Deployment advice for IPv6 that will allow stable and secure IPv6
only experience, even if IPv4 support is present
o Ensure support for IPv6 is efficient and does not impact the
performance of the underlying network and in turn the customer
experience
o Allow for the greatest flexibility across host implementation to
allow for the widest range of addressing and configuration
mechanisms to be employed. The goal here is the ensure that the
widest population of UE implementations can leverage the
availability of IPv6
o Lay the technological foundation for future work related to the
use of IPv6 over shared media requiring optimized subscriber
management
o Two devices (subscriber/hosts), both attached to the same provider
managed shared network should only be able to communicate through
the provider managed First Hop Router
o Provide guidelines regarding best common practices around IPv6
neighborship discovery and IPv6 address managent settings between
the First Hop router and directly connected hosts/subscribers.
3. Design Princinples
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 directy connected devices and remote devices.
The work detailed in this document is focussed to provide details
regarding best common practices of the IPv6 neighborship discovery
and related IPv6 address management settings between the First Hop
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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
hosts/subscribers devices connected to the provider managed shared
network with a unique IPv6 prefix while at the same functioning as
control-plane anchor point to make sure that each subscriber is
receiving the 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, 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 a few important parameters for the EU/subscriber to
consume: (1) a /64 prefix and (2) flags. The /64 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:
o M-flag = 0 (UE/subscriber address is not managed through DHCPv6),
this flag may be set to 1 in the future if/when DHCPv6 prefix
delegation support is desired)
o O-flag = 1 (DHCPv6 is used to request configuration information
i.e. DNS, NTP information, not for IPv6 addressing)
o A-flag = 1 (The UE/subscriber can configure itself using SLAAC)
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o L-flag = 0 (The UE/subscriber is off-link, which means that the
UE/subscriber will send packets ALWAYS to his default gateway,
even if the destination is within the range of the /64 prefix)
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
maximize 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 /64 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.
Now that 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 Neighbourship 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 WLAN-GW MUST
therefore be lower than the preferred lifetime. As a 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 reference table of the key IPv6 router discovery and
neighbor discovery timers for provider managed shared networks:
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o IPv6 Router Advertisement Interval = 300s
o IPv6 Router LifeTime = 3600s
o Reachable time = 30s
o IPv6 Valid Lifetime = 3600s
o IPv6 Preferred Lifetime = 1800s
o Retransmit timer = 0s
The stateless nature of the UE/subscriber IPv6 SLAAC connectivity
model provides value to make sure that the UE/subscriber context is
timely removed from the First Hop Router to avoid ongoing resource
depletion. A possible solution is to use a subscriber inactivity
timer which after tracking a pre-defined (currently unspecified) # 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 utilize RFC 4941 RFC4941
[RFC4941] temporary 'private' addresses. This can lead to the
consequence that a UE has multiple /128 addresses from the same IPv6
prefix. The First Hop Provder 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. Future work
o Informational draft regarding WLAN IPv6 Deployment technology
experiences roll-out
7. IANA Considerations
No IANA considerations are defined at this time.
8. Security Considerations
No Additional Security Considerations are made in this document.
9. Acknowledgements
The authors would like to thank the following, in alphabetical order,
for their contributions:
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Lorenzo Colitti, Killian Desmedt, Brad Hilgenfeld, Wim Henderickx,
Erik Kline, Thomas Lynn, Phil Sanderson, Colleen Szymanik, Sanjay
Wadhwa
10. References
10.1. Normative References
[RFC3315] Droms, R., Ed., 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, <http://www.rfc-editor.org/info/rfc3315>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<http://www.rfc-editor.org/info/rfc4862>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<http://www.rfc-editor.org/info/rfc4941>.
[RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 6106, DOI 10.17487/RFC6106, November 2010,
<http://www.rfc-editor.org/info/rfc6106>.
[RFC6180] Arkko, J. and F. Baker, "Guidelines for Using IPv6
Transition Mechanisms during IPv6 Deployment", RFC 6180,
DOI 10.17487/RFC6180, May 2011,
<http://www.rfc-editor.org/info/rfc6180>.
10.2. Informative References
[I-D.ietf-v6ops-v4v6tran-framework]
Carpenter, B., Jiang, S., and V. Kuarsingh, "Framework for
IP Version Transition Scenarios", draft-ietf-v6ops-
v4v6tran-framework-02 (work in progress), July 2011.
[RFC6343] Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
RFC 6343, DOI 10.17487/RFC6343, August 2011,
<http://www.rfc-editor.org/info/rfc6343>.
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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
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