Internet DRAFT - draft-liu-softwire-lw4over6-dynamic-provisioning
draft-liu-softwire-lw4over6-dynamic-provisioning
Network Working Group C. Liu
Internet-Draft Q. Sun
Intended status: Informational J. Wu
Expires: September 22, 2016 Tsinghua University
I. Farrer
Deutsche Telekom AG
March 21, 2016
Dynamic IPv4 Provisioning for Lightweight 4over6
draft-liu-softwire-lw4over6-dynamic-provisioning-01
Abstract
Lightweight 4over6 [RFC7596] is an IPv4 over IPv6 hub-and-spoke
mechanism that provides overlay IPv4 services in an IPv6-only access
network. It uses a deterministic, DHCPv6 based method for the
provisioning of IPv4 addresses and port sets to customer CE devices.
This document describes how existing specifications can be used for
the dynamic IPv4 provisioning of Lightweight 4over6, based on DHCPv4
over DHCPv6 [RFC7341].
Status of This Memo
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This Internet-Draft will expire on September 22, 2016.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Architecture Overview . . . . . . . . . . . . . . . . . . . . 4
4. Lightweight4over6 Dynamic Provisioning Process . . . . . . . 5
4.1. Client IPv6 Addressing . . . . . . . . . . . . . . . . . 5
4.2. DHCPv6 Configuration . . . . . . . . . . . . . . . . . . 5
4.3. DHCPv4 over DHCPv6 Function . . . . . . . . . . . . . . . 5
4.4. lwAFTR Binding Table Maintenance . . . . . . . . . . . . 5
4.4.1. Co-located lwAFTR/DHCP4o6 Binding Table Maintenance . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5.1. Data Retention Requirements . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Lightweight 4over6 [RFC7596] provides IPv4 access over an IPv6
network in hub-and-spoke softwire architecture. In Lightweight
4over6, each Lightweight B4 (lwB4) is assigned a full, or shared
(port-restricted) IPv4 address to be used for IPv4 communication.
Provisioning the lwB4 with its IPv4 address, port set and other
parameters necessary for building the softwire is the core function
of the Lightweight 4over6 control plane.
[RFC7596] describes the use of DHCPv6 for deterministic IPv4
provisioning. The IPv4 address, port set ID (PSID) and address of
the lwAFTR are carried in DHCPv6 options defined in [RFC7598].
However, the deterministic provisioning of the IPv4 parameters
imposes restrictions on the deployment:
o The IPv4 address' life time is bound to the client's IPv6 tunnel
endpoint life time
o The tunnel must be initiated from a fixed and predictable /64
prefix in the home network topology
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o The IPv4 address and PSID need to be embedded into the IID of the
clients' /128 IPv6 address
o IPv4 address resources are permanently reserved for a client
whether it is active or not. This results in less efficient
public IPv4 address usage
This document describes the deployment of Lightweight 4over6 using
DHCPv4 over DHCPv6 for dynamic IPv4 address provisioning. The main
advantages of using a dynamic provisioning model over a deterministic
model are as follows:
o No inherent restrictions on the IPv6 source address within the
customer internal network that the client uses for sourcing its
tunneled traffic
o The lifetimes of IPv6 and IPv4 addresses are decoupled, allowing
for more flexibility in the service provider's addressing policy
o Inactive clients' addresses can be released/reclaimed for
allocation to active clients, so more efficient address usage is
possible
Since DHCPv4 over IPv4 cannot be used natively in a single stack IPv6
network, DHCPv4 over DHCPv6 (DHCP4o6) [RFC7341] allows DHCPv4
functionality to be trasported over a pure in IPv6 network by placing
DHCPv4 messages within DHCPv6 messages.
[I-D.fsc-softwire-dhcp4o6-saddr-opt] defines a DHCP4o6 based
mechanism for the lwB4 to inform the server of its IPv6 tunnel source
address.
The architecture which is described in this document can be
implemented with or without the sharing of IPv4 addresses between
multiple clients. If IPv4 address sharing is required, then
[RFC7618] describes the changes necessary extensions to the DHCPv4
server and client provisioning for the allocation and lease
management of shared IPv4 addresses.
2. Terminology
Terminology defined in [RFC7341] and [RFC7596] is used extensively
throughout this document.
Unless stated otherwise, the term "lwB4" should be understood to mean
a stateful lwB4 using DHCP4o6 for dynamic IPv4 provisioning.
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3. Architecture Overview
There are four functional elements which make up the architecture.
Although these are shown as being seperate entities, it is possibile
that one or more of the operator side functions might be performed by
a single device.
________ __________
| | | |
| DHCPv6 | | DHCP4o6 |
| Server | | Server |
|________| |__________|
^ / \
1 | 2 / \ 3
___v____ / \ ________
| | | |
| lwB4 |<---------------->| lwAFTR |
|________| Data Plane |________|
The numbers in each of the provisioning flows are described in more
detail below.
Figure 1: Dynamic lw4o6 Provisioning Model
The process for provisioning Lightweight 4over6 using DHCP4o6 is as
follows:
1. The lwB4 uses DHCPv6[RFC3315] to obtain its basic configuration.
OPTION_DHCP4_O_DHCP6_SERVER (88) is included in the client's ORO.
The IPv6 address of at least one DHCP4o6 server is given in the
response.
2. The client sends a DHCPv4 DISCOVER message in a DHCP4o6 message
to the DHCP4o6 server(s). The rest of the message flow proceeds
as per Section 5 of [I-D.fsc-softwire-dhcp4o6-saddr-opt]. The
result is that the client is provisioned with the Ipv6 address of
the lwAFTR, an IPv4 address and (optionally) a range of source
ports. The server has the /128 IPv6 address that the client will
use its tunnel source associated with the IPv4 lease.
3. lwAFTR binding table maintenance is achieved by using NETCONF
[RFC6241]. The YANG model for lw4o6 is defined in
[I-D.sun-softwire-yang].
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4. Lightweight4over6 Dynamic Provisioning Process
This section describes the dynamic provisioning process of
Lightweight 4over6 in more detail.
4.1. Client IPv6 Addressing
Before attempting the DHCP4o6 configuration process to obtain IPv4
configuration, the lwB4 needs to have an IPv6 address of a suitable
scope to allow communication with the lwAFTR (e.g. a link-local
address cannot be used). There are no restrictions on how the
client's IPv6 address is provisioned, (e.g. SLAAC, DHCPv6 or some
other mechanisms).
4.2. DHCPv6 Configuration
The initial configuration step is for the lwB4 to perform DHCPv6 to
retrieve the DHCP 4o6 server's IPv6 address. The DHCPv6 server
provides the DHCP 4o6 server's IPv6 address by
OPTION_DHCP4_O_DHCP6_SERVER as defined in [RFC7341].
4.3. DHCPv4 over DHCPv6 Function
Once the lwB4 has acquired the IPv6 address of the DHCP4o6 server,
stateful configuration using DHCP4o6 is performed to obtain an IPv4
address and port set. The PSID is conveyed using DCHPv4
OPTION_V4_PORTPARAMS (159) as decribed in [RFC7618]. The lwB4
includes one of its active IPv6 addresses as the IPv6 tunnel source
address in this message flow with the DHCP 4o6 server, and receives
the lwAFTR's tunnel address through DHCP4o6, as described in section
4 of [I-D.fsc-softwire-dhcp4o6-saddr-opt].
4.4. lwAFTR Binding Table Maintenance
In figure 1 above, the lwAFTR is not co-located with the DHCP 4o6
server. With this architecture, NETCONF [RFC6241] is used for
syncronising client DHCP4o6 provisioning and the lwAFTR binding
table. A YANG model for lw4o6 is defined in [I-D.sun-softwire-yang].
In this deployment model, the DHCP4o6 server and lwAFTR also
implements a NETCONF server. When an IPv4 leasing event occurs (e.g.
DHCPACK/DHCPRELEASE messages), the DHCP4o6 server informs the
operator's centralised configuration database of the change.
The operator's configuration database will then use NETCONF to update
the lwAFTR of the relevant change by adding or removing the binding
table entry which matches the DHCP4o6 server's IPv4 address lease.
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4.4.1. Co-located lwAFTR/DHCP4o6 Binding Table Maintenance
In this deployment scenario, the DHCP4o6 and lwAFTR functions are
both active on the same device. Here, the lwAFTR maintains its
binding table as per section 6.1 of [RFC7596] and is synchronized
with DHCP4o6 process. The following DHCP4o6 messages trigger binding
table modification:
DHCPACK: Generated by the DHCP4o6 server, triggers lwAFTR to add a
new entry or modify an existing entry.
DHCPRELEASE: Generated by lwB4, triggers lwAFTR to delete an
existing entry.
When the DHCP4o6 server generates a DHCPACK message, the lwAFTR looks
up the binding table using the lwB4's IPv4 address and PSID as index.
If there is an existing entry found, the lwAFTR updates the IPv6
address and lifetime fields of the entry; otherwise the lwAFTR
creates a new entry accordingly. When the DHCP4o6 server receives a
DHCPRELEASE message , the lwAFTR looks up the binding table using the
lwB4's IPv6 address, IPv4 address and PSID as index. The lwAFTR
deletes the entry either by removing it from the binding table or by
marking the lifetime field with an invalid value (e.g. 0).
5. Security Considerations
Security considerations in [RFC7596] and [RFC7341] are also relevant
here.
The DHCP message triggered binding table maintenance may be used by
an attacker to send fake DHCP messages to lwAFTR. The operator
network should deploy [RFC2827] to prevent this kind of attack.
5.1. Data Retention Requirements
In some countries, regulations require a service providers to retain
the necessary information to link IP information to a specific
customer. With a deterministic provisioning model, any individual
client will always receive a pre-determined set of IPv4 provisioning
requirements. In this scenario, the logging requirement may be met
by retaining information on how the DHCPv6 server has been pre-
provisioned, with timestamp information on when changes to the pre-
provisioning have come into effect.
The dynamic provisioning model that is described in this document
brings an additional logging requirement to the service provider: The
retention logs holding allocated IPv4 address and ports, the
associated IPv6 tunnel endpoint and timestamps marking the start and
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end of the lease. This is a higher logging overheard than
deterministic provisioning, but is in line with the amount of logging
that service providers currently have.
6. IANA Considerations
This document does not include an IANA request.
7. References
7.1. Normative References
[I-D.fsc-softwire-dhcp4o6-saddr-opt]
Farrer, I., Sun, Q., and Y. Cui, "DHCPv4 over DHCPv6
Source Address Option", draft-fsc-softwire-dhcp4o6-saddr-
opt-04 (work in progress), November 2015.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <http://www.rfc-editor.org/info/rfc2827>.
[RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport",
RFC 7341, DOI 10.17487/RFC7341, August 2014,
<http://www.rfc-editor.org/info/rfc7341>.
[RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
Farrer, "Lightweight 4over6: An Extension to the Dual-
Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596,
July 2015, <http://www.rfc-editor.org/info/rfc7596>.
[RFC7618] Cui, Y., Sun, Q., Farrer, I., Lee, Y., Sun, Q., and M.
Boucadair, "Dynamic Allocation of Shared IPv4 Addresses",
RFC 7618, DOI 10.17487/RFC7618, August 2015,
<http://www.rfc-editor.org/info/rfc7618>.
7.2. Informative References
[I-D.sun-softwire-yang]
Sun, Q., Wang, H., Cui, Y., Farrer, I., Boucadair, M., and
R. Asati, "YANG Data Model for IPv4-in-IPv6 Softwire",
draft-sun-softwire-yang-04 (work in progress), October
2015.
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[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>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<http://www.rfc-editor.org/info/rfc6887>.
[RFC7598] Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for
Configuration of Softwire Address and Port-Mapped
Clients", RFC 7598, DOI 10.17487/RFC7598, July 2015,
<http://www.rfc-editor.org/info/rfc7598>.
Authors' Addresses
Cong Liu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5822
Email: cong-liu13@mails.tsinghua.edu.cn
Qi Sun
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5822
Email: sunqi@csnet1.cs.tsinghua.edu.cn
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Jianping Wu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5983
Email: jianping@cernet.edu.cn
Ian Farrer
Deutsche Telekom AG
CTO-ATI,Landgrabenweg 151
Bonn, NRW 53227
Germany
Email: ian.farrer@telekom.de
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