v6ops Working Group G. Van de Velde
Internet-Draft Cisco Systems
Expires: August 16, 2008 J. Brozowski
Comcast Cable
S. Miyakawa
NTT Communications
February 13, 2008
CPE Default Route Detection
<draft-vandevelde-v6ops-cpe-default-route-detection-00.txt>
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Copyright (C) The IETF Trust (2008).
Abstract
When the CPE (Customer Premisses Equipment) device is a routed IPv6
device, then detection automation of the upstream connectivity (i.e.
the default-route) has not been uniformly described. There are many
CPE vendors, and they may have many technologies to achieve this
goal. This document provides an overview of the problem space, while
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identifying various options within the solution space.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem statement . . . . . . . . . . . . . . . . . . . . . . . 3
3. Alternatives for Default Route Detection . . . . . . . . . . . 4
3.1. Manual Route Configuration on the CPE . . . . . . . . . . . 4
3.2. Routing protocol between CPE and upstream router . . . . . 4
3.3. Extension of DHCPv6 with a default-router option . . . . . 4
3.4. CPE has both Router and Host functionality . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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1. Introduction
A Service Provider (SP) providing IPv6 connectivity to customer
networks may want to automate provisioning of IPv6 prefixes and other
configuration information to reduce errors and human interaction
towards CPE devices. An available tool to achieve this goal is
DHCP-PD [1]. DHCP-PD allows for both automated assignment of IPv6
prefixes and of configuration parameter allocation to a customer
network.
Where DHCP-PD [1] typical delivers information about the allocated
address space to a customer network combined with other configuration
parameters, it does not provide information to the customer network
about the upstream connectivity through the SP.
This document will provide a problem definition to help the CPE
detect its upstream connectivity while providing insight about the
potential solution space.
2. Problem statement
If assumed that a customer network is comprised of at least one CPE
where the CPE is providing network connectivity (routed) to nodes on
the customer network. In this case the CPE is assumed to be more
than just a single host or node. It is also assumed that the CPE
device is dynamically allocating network and configuration
information through DHCP-PD. The CPE may segment received address
space and allocate it towards the various interfaces available to the
CPE. Techniques for the sub-allocation of delegated IPv6 address
space is out of scope for this document.
If the customer network consists out of multiple routers
hierarchically organized then only the CPE performing DHCP-PD with
the SP network can be used to obtain an parent prefix from which sub-
allocations can be derived. Additional care needs to be taken to
distribute the through DHCP-PD received IPv6 address space on the CPE
amongst the set of customer routers. These techniques and procedures
(i.e. hierachical DHCP services) are outside the scope of this
document.
Whereas the CPE directly connected to the SP has awareness of the
Service Provider allocated address space it is not made dynamically
aware of the upstream path to install upstream routing entries,
specifically the default route for the customer network. The
following sections outline techniques that can be used to obtain and
populate (default-)route information in the CPE.
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3. Alternatives for Default Route Detection
3.1. Manual Route Configuration on the CPE
The administrator of the CPE may have out-of-band awareness of the
default gateway. In this case the administrator may configure routes
manually on the CPE. However, even if this option may seem trivial,
it is open to human mistakes and requires human action. Hence, it is
not a preferenced method of operation for fully automated CPE
provisioning.
3.2. Routing protocol between CPE and upstream router
If the CPE has routing capabilities then routing information can be
exchanged between CPE and the SP access router. A dynamic routing
protocol can be used to achieve this. This solution can be useful if
the service provider router has a limited set of CPE's connected.
This is due to scalability and possible state-maintenance which tend
to require significant amount of bandwidth and processing power.
This option will seldomly be useful for home networks where there are
often large volumes of devices that connect to a single service
provider access router.
3.3. Extension of DHCPv6 with a default-router option
Currently there is no option specified for DHCPv6 to identify the
default-router that may be used by the device. If this option were
available then it could be used by the CPE to detect its default-
router and populate the required routing information on the CPE.
Specification of this DHCPv6 option and device behavior to acquire
and populate the same is out of scope for this document.
3.4. CPE has both Router and Host functionality
RFC4861 [2] section 6.2.7. Router Advertisement Consistency defines
the behavior of routers related to the processing of Router
Advertisement messages. It is specified that routers are to inspect
router advertisement messages to validate the contents of the same
relative to the link. RFC4861 [2] also indicates that any additional
behavior beyond this related to the router is out of scope for the
RFC.
Further, section 6.3.4. Processing Received Router Advertisements of
RFC4861 [2] specifies host behavior relative to the processing of
router advertisements. Specifically, the detection and installation
of default routes is clearly specified.
Since a CPE can in essence be both router and host. The text in
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RFC4861 [2] does not clearly specify how such a device should be
expected to behave related to the processing of router advertisements
specifically related to the installation of default routes.
A CPE device that is acting as a host and router may listen to Router
Advertisements from the SP network and process them as a host to
identify/detect its default-router. In addition this default-router
information can be used to install routes on the CPE towards external
upstream services and devices. This option can provide a scalable
solution for (default-)route detection and population on CPE's based
upon received Router Advertisement messages. This mechanism does not
require any protocol changes or additional traffic on the wire.
However, the behavior of the CPE relative to the processing of Router
Advertisements requires additional specification.
4. IANA Considerations
There are no extra IANA consideration for this document.
5. Security Considerations
If a CPE device acts as both Router as Host then it will inherit the
secruity for both Host as Router as specified in RFC4861 [2]. For
the remaining there are no additional security considerations for
this document.
6. Acknowledgements
Concept thinking has been done with Ralph Droms, Bernie Volz, Eric
Levy-Abegnoli during IETF70.
7. References
7.1. Normative References
7.2. Informative References
[1] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[2] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor
Discovery for IP version 6 (IPv6)", RFC 4861, September 2007.
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Authors' Addresses
Gunter Van de Velde
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Phone: +32 2704 5473
Email: gunter@cisco.com
John Jason Brzozowski
Comcast Cable
1800 Bishops Gate Boulevard
Mt. Laurel, NJ 08054
USA
Phone: +1 609 377 6594
Email: john_brzozowski@cable.comcast.com
Shin Miyakawa
NTT Communications
Tokyo,
Japan
Phone: +81-3-6800-3262
Email: miyakawa@nttv6.jp
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