Basic Requirements for IPv6 Customer Edge Routers
draft-ietf-v6ops-ipv6-cpe-router-05

Abstract

This document specifies requirements for an IPv6 Customer Edge (CE) router. Specifically, the current version of this document focuses on the basic provisioning of an IPv6 CE router and the provisioning of IPv6 hosts attached to it.

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/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work in progress.”

This Internet-Draft will expire on November 12, 2010.

Copyright Notice

Copyright (c) 2010 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1.  Introduction
    1.1.  Requirements Language
2.  Terminology
3.  Architecture
    3.1.  Current IPv4 End-user Network Architecture
    3.2.  IPv6 End-user Network Architecture
4.  Requirements
    4.1.  General Requirements
    4.2.  WAN Side Configuration
    4.3.  LAN Side Configuration
    4.4.  Security Considerations
5.  Acknowledgements
6.  Contributors
7.  IANA Considerations
8.  References
    8.1.  Normative References
    8.2.  Informative References
§  Authors' Addresses

1.  Introduction

This document defines basic IPv6 features for a residential or small office router referred to as an IPv6 CE router. Typically these routers also support IPv4.

Mixed environments of dual-stack hosts and IPv6-only hosts (behind the CE router) can be more complex if the IPv6-only devices are using a translator to access IPv4 servers [I‑D.ietf‑behave‑v6v4‑framework] (Baker, F., Li, X., Bao, C., and K. Yin, “Framework for IPv4/IPv6 Translation,” March 2010.). Support for such mixed environments is not in scope of this document.

This document specifies how an IPv6 CE router automatically provisions its WAN interface, acquires address space for provisioning of its LAN interfaces and fetches other configuration information from the service provider network. Automatic provisioning of more complex topology than a single router with multiple LAN interfaces is out of scope for this document.

See [RFC4779] (Asadullah, S., Ahmed, A., Popoviciu, C., Savola, P., and J. Palet, “ISP IPv6 Deployment Scenarios in Broadband Access Networks,” January 2007.) for a discussion of options available for deploying IPv6 in Service Provider access networks.

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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

2.  Terminology

End-user Network

one or more links attached to the IPv6 CE router that connect IPv6 hosts.

IPv6 Customer Edge router

a node intended for home or small office use which forwards IPv6 packets not explicitly addressed to itself. The IPv6 CE router connects the end-user network to a service provider network.

IPv6 host

any device implementing an IPv6 stack receiving IPv6 connectivity through the IPv6 CE router

LAN interface

an IPv6 CE router's attachment to a link in the end-user network. Examples are Ethernets (simple or bridged), 802.11 wireless or other LAN technologies. An IPv6 CE router may have one or more network layer LAN Interfaces.

Service Provider

an entity that provides access to the Internet. In this document, a Service Provider specifically offers Internet access using IPv6, and may also offer IPv4 Internet access. The Service Provider can provide such access over a variety of different transport methods such as DSL, cable, wireless, and others.

WAN interface

an IPv6 CE router's attachment to a link used to provide connectivity to the Service Provider network; example link technologies include Ethernets (simple or bridged), PPP links, Frame Relay, or ATM networks as well as Internet-layer (or higher-layer) "tunnels", such as tunnels over IPv4 or IPv6 itself.

3.  Architecture

3.1.  Current IPv4 End-user Network Architecture

An end-user network will likely support both IPv4 and IPv6. It is not expected that an end-user will change their existing network topology with the introduction of IPv6. There are some differences in how IPv6 works and is provisioned which has implications for the network architecture. A typical IPv4 end-user network consist of a "plug and play" router with NAT functionality and a single link behind it, connected to the Service Provider network.

A typical IPv4 NAT deployment by default blocks all incoming connections. Opening of ports is typically allowed using UPnP IGD [UPnP‑IGD] (UPnP Forum, “Universal Plug and Play (UPnP) Internet Gateway Device (IGD),” November 2001.) or some other firewall control protocol.

Another consequence of using private address space in the end-user network is that it provides stable addressing, i.e. it never changes even when you change Service Providers, and the addresses are always there even when the WAN interface is down or the customer edge router has not yet been provisioned.

Rewriting addresses on the edge of the network also allows for some rudimentary multi-homing; even though using NATs for multi-homing does not preserve connections during a fail-over event [RFC4864] (Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and E. Klein, “Local Network Protection for IPv6,” May 2007.).

Many existing routers support dynamic routing, and advanced end users can build arbitrary, complex networks using manual configuration of address prefixes combined with a dynamic routing protocol.

3.2.  IPv6 End-user Network Architecture

The end-user network architecture for IPv6 should provide equivalent or better capabilities and functionality than the current IPv4 architecture.

The end-user network is a stub network. Figure 1 illustrates the model topology for the end-user network.

An example of a typical end-user network.

                  +-------+-------+                   \
                  |   Service     |                    \
                  |   Provider    |                     | Service
                  |    Router     |                     | Provider
                  +-------+-------+                     | network
                          |                             /
                          | Customer                   /
                          | Internet connection       /
                          |
                   +------+--------+                  \
                   |     IPv6      |                   \
                   | Customer Edge |                    \
                   |    Router     |                    /
                   +---+-------+-+-+                   /
       Network A       |       |   Network B          | End-User
 ---+-------------+----+-    --+--+-------------+---  |network(s)
    |             |               |             |      \
+----+-----+ +-----+----+     +----+-----+ +-----+----+  \
|IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |  /
|          | |          |     |          | |          | /
+----------+ +-----+----+     +----------+ +----------+/

This architecture describes the:

• Basic capabilities of an IPv6 CE router
• Provisioning of the WAN interface connecting to the Service Provider
• Provisioning of the LAN interfaces

Unique Local IPv6 Unicast Addresses (ULA) [RFC4193] (Hinden, R. and B. Haberman, “Unique Local IPv6 Unicast Addresses,” October 2005.) are used by hosts communicating within the End-user Network; this is functionally similar to RFC1918 addresses used within an IPv4 End-user Network. The IPv6 CE router defaults to acting as the demarcation point between two networks by providing a ULA boundary, a multicast zone boundary and ingress and egress traffic filters.

For IPv6 multicast traffic the IPv6 CE router may act as an MLD proxy [RFC4605] (Fenner, B., He, H., Haberman, B., and H. Sandick, “Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying"),” August 2006.) and may support a dynamic multicast routing protocol.

The IPv6 CE router may be manually configured in an arbitrary topology with a dynamic routing protocol. Automatic provisioning and configuration is described for a single IPv6 CE router only.

4.  Requirements

4.1.  General Requirements

The IPv6 CE router is responsible for implementing IPv6 routing; that is, the IPv6 CE router must look up the IPv6 Destination address in its routing table to decide to which interface it should send the packet.

In this role, the IPv6 CE router is responsible for ensuring that traffic using its ULA addressing does not go out the WAN interface, and does not originate from the WAN interface.

G-1:

An IPv6 CE router is an IPv6 node according to the IPv6 Node Requirements (Jankiewicz, E., Loughney, J., and T. Narten, “IPv6 Node Requirements RFC 4294-bis,” March 2010.) [I‑D.ietf‑6man‑node‑req‑bis] specification.

G-2:

The IPv6 CE router MUST implement ICMP according to [RFC4443] (Conta, A., Deering, S., and M. Gupta, “Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification,” March 2006.). In particular point to point links MUST be handled as described in section 3.1 of [RFC4443] (Conta, A., Deering, S., and M. Gupta, “Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification,” March 2006.).

G-3:

The IPv6 CE router MUST NOT forward any IPv6 traffic between its LAN Interface(s) and its WAN Interface until the router has successfully completed the IPv6 address acquisition process.

4.2.  WAN Side Configuration

The IPv6 CE router will need to support connectivity to one or more access network architectures. This document describes an IPv6 CE router that is not specific to any particular architecture or Service Provider, and supports all commonly used architectures.

IPv6 Neighbor Discovery and DHCPv6 protocols operate over any type of IPv6 supported link-layer and there is no need for a link-layer specific configuration protocol for IPv6 network layer configuration options as in e.g. PPP IPCP for IPv4. This section makes the assumption that the same mechanism will work for any link-layer, be it Ethernet, DOCSIS, PPP or others.

WAN side requirements:

W-1:

When the router is attached to the WAN interface link it MUST act as an IPv6 host for the purposes of stateless or stateful interface address assignment ([RFC4862] (Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” September 2007.)/[RFC3315] (Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, “Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” July 2003.)).

W-2:

The IPv6 CE router MUST generate a link-local address and finish Duplicate Address Detection according to [RFC4862] (Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” September 2007.) prior to sending any Router Solicitations on the interface. The source address used in the subsequent Router Solicitation MUST be the link-local address on the WAN interface.

W-3:

Absent of other routing information the IPv6 CE router MUST use Router Discovery as specified in [RFC4861] (Narten, T., Nordmark, E., Simpson, W., and H. Soliman, “Neighbor Discovery for IP version 6 (IPv6),” September 2007.) to discover a default router(s) and install default route(s) in its routing table with the discovered router's address as the next-hop.

W-4:

The router MUST act as a requesting router for the purposes of DHCPv6 prefix delegation ([RFC3633] (Troan, O. and R. Droms, “IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6,” December 2003.)).

W-5:

DHCPv6 address assignment (IA_NA) and DHCPv6 prefix delegation (IA_PD) SHOULD be done as a single DHCPv6 session.

Link-layer requirements:

WLL-1:

If the WAN interface supports Ethernet encapsulation, then the IPv6 CE router MUST support IPv6 over Ethernet [RFC2464] (Crawford, M., “Transmission of IPv6 Packets over Ethernet Networks,” December 1998.).

WLL-2:

If the WAN interface supports PPP encapsulation the IPv6 CE router MUST support IPv6 over PPP [RFC5072] (S.Varada, Haskins, D., and E. Allen, “IP Version 6 over PPP,” September 2007.).

WLL-3:

If the WAN interface supports PPP encapsulation, in a dual-stack environment with IPCP and IPV6CP running over one PPP logical channel, the NCPs MUST be treated as independent of each other and start and terminate independently.

Address assignment requirements:

WAA-1:

The IPv6 CE router MUST support SLAAC [RFC4862] (Thomson, S., Narten, T., and T. Jinmei, “IPv6 Stateless Address Autoconfiguration,” September 2007.).

WAA-2:

The IPv6 CE router MUST follow the recommendation in [I‑D.ietf‑6man‑ipv6‑subnet‑model] (Singh, H., Beebee, W., and E. Nordmark, “IPv6 Subnet Model: the Relationship between Links and Subnet Prefixes,” April 2010.) and in particular the handling of the L-flag in the Router Advertisement Prefix Information Option.

WAA-3:

The IPv6 CE router MUST support DHCPv6 [RFC3315] (Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, “Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” July 2003.) client behavior.

WAA-4:

The IPv6 CE router MUST be able to support the following DHCPv6 options: IA_NA, Reconfigure Accept [RFC3315] (Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, “Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” July 2003.), DNS_SERVERS [RFC3646] (Droms, R., “DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” December 2003.).

WAA-5:

The IPv6 CE router SHOULD support the DHCPv6 SNTP option [RFC4075] (Kalusivalingam, V., “Simple Network Time Protocol (SNTP) Configuration Option for DHCPv6,” May 2005.) and the Information Refresh Time Option [RFC4242] (Venaas, S., Chown, T., and B. Volz, “Information Refresh Time Option for Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” November 2005.).

WAA-6:

If the IPv6 CE router receives an RA message (described in [RFC4861] (Narten, T., Nordmark, E., Simpson, W., and H. Soliman, “Neighbor Discovery for IP version 6 (IPv6),” September 2007.)) with the M-flag set to 1, the IPv6 CE router MUST do DHCPv6 address assignment (request an IA_NA option).

WAA-7:

If the IPv6 CE router is unable to assign address(es) through SLAAC it MAY do DHCPv6 address assignment (request an IA_NA) even if the M-flag is set to 0.

WAA-8:

If the IPv6 CE router does not acquire global IPv6 address(es) from either SLAAC or DHCPv6, then it MUST create global IPv6 address(es) from its delegated prefix(es) and configure those on one of its internal virtual network interfaces.

WAA-9:

As a router the IPv6 CE router MUST follow the weak host model [RFC1122] (Braden, R., “Requirements for Internet Hosts - Communication Layers,” October 1989.). When originating packets out an interface it will use a source address from another of its interfaces if the outgoing interface does not have an address of suitable scope.

Prefix Delegation requirements:

WPD-1:

The IPv6 CE router MUST support DHCPv6 prefix delegation requesting router behavior as specified in [RFC3633] (Troan, O. and R. Droms, “IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6,” December 2003.) (IA_PD option).

WPD-2:

The IPv6 CE router MAY indicate as a hint to the delegating router the size of the prefix it requires. If so, it MUST ask for a prefix large enough to assign one /64 for each of its interfaces rounded up to the nearest nibble and MUST be configurable to ask for more.

WPD-3:

The IPv6 CE router MUST be prepared to accept a delegated prefix size different from what is given in the hint. If the delegated prefix is too small to address all of its interfaces, the IPv6 CE router SHOULD log a system management error.

WPD-4:

The IPv6 CE router MUST always initiate DHCPv6 prefix delegation, regardless of the M and O-flags in a received Router Advertisement message.

WPD-5:

If the IPv6 CE Router initiates DHCPv6 before receiving a Router Advertisement it MUST also request an IA_NA option in DHCPv6.

WPD-6:

If the delegated prefix(es) are aggregate route(s) of multiple, more-specific routes, the IPv6 CE router MUST discard packets that match the aggregate route(s), but not any of the more-specific routes. In other words, the next-hop for the aggregate route(s) should be the null destination. This is necessary to prevent forwarding loops when some addresses covered by the aggregate are not reachable [RFC4632] (Fuller, V. and T. Li, “Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan,” August 2006.).

(a)

The IPv6 CE router SHOULD send an ICMPv6 Destination Unreachable according to section 3.1 (Conta, A., Deering, S., and M. Gupta, “Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification,” March 2006.) [RFC4443] back to the source of the packet, if the packet is to be dropped due to this rule.

WPD-7:

If the IPv6 CE router requests both an IA_NA and an IA_PD in DHCPv6, it MUST accept an IA_PD in DHCPv6 Advertise/Reply messages, even if the message does not contain any addresses (IA_NA options with status code equal to NoAddrsAvail).

WPD-8:

By default an IPv6 CE router MUST NOT initiate any dynamic routing protocol on its WAN interface.

4.3.  LAN Side Configuration

The IPv6 CE router distributes configuration information obtained during WAN interface provisioning to IPv6 hosts and assists IPv6 hosts in obtaining IPv6 addresses. It also supports connectivity of these devices in the absence of any working WAN interface.

An IPv6 CE router is expected to support an IPv6 end-user network and IPv6 hosts that exhibit the following characteristics:

1. Link-local addresses are insufficient for allowing IPv6 applications to communicate with each other in the end-user network. The IPv6 CE router will need to enable this communication by providing globally-scoped unicast addresses or ULAs [RFC4193] (Hinden, R. and B. Haberman, “Unique Local IPv6 Unicast Addresses,” October 2005.) whether or not WAN connectivity exists.
2. IPv6 hosts should be capable of using SLAAC and may be capable of using DHCPv6 for acquiring their addresses.
3. IPv6 hosts may use DHCPv6 for other configuration information, such as the DNS_SERVERS option for acquiring DNS information.

Unless otherwise specified, the following requirements apply to the IPv6 CE router's LAN interfaces only.

Requirements:

L-1:

The IPv6 CE router MUST support ULA addressing [RFC4193] (Hinden, R. and B. Haberman, “Unique Local IPv6 Unicast Addresses,” October 2005.).

L-2:

The IPv6 CE router MUST have a ULA prefix that it maintains consistently across reboots.

L-3:

The value of the ULA prefix SHOULD be user configurable.

L-4:

By default the IPv6 CE router MUST act as a site border router according to section 4.3 of [RFC4193] (Hinden, R. and B. Haberman, “Unique Local IPv6 Unicast Addresses,” October 2005.) and filter packets with Local IPv6 source or destination addresses accordingly.

L-5:

The IPv6 CE router MUST support router behavior according to Neighbor Discovery for IPv6 [RFC4861] (Narten, T., Nordmark, E., Simpson, W., and H. Soliman, “Neighbor Discovery for IP version 6 (IPv6),” September 2007.).

L-6:

The IPv6 CE router MUST assign a separate /64 from its delegated prefix(es) (and ULA prefix if configured to provide ULA addressing) for each of its LAN interfaces.

L-7:

The IPv6 CE router MUST make each LAN interface an advertising interface according to [RFC4861].

L-8:

In Router Advertisements messages, the Prefix Information Option's A and L-flags MUST be set to 1 by default.

L-9:

The A and L-flags setting SHOULD be user configurable.

L-10:

The IPv6 CE router MUST support a DHCPv6 server capable of IPv6 address assignment according to [RFC3315] (Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, “Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” July 2003.) OR a stateless DHCPv6 server according to [RFC3736] (Droms, R., “Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6,” April 2004.) on its LAN interfaces.

L-11:

Unless the IPv6 CE router is configured to support the DHCPv6 IA_NA option, it SHOULD set M=0 and O=1 in its Router Advertisement messages [RFC4861] (Narten, T., Nordmark, E., Simpson, W., and H. Soliman, “Neighbor Discovery for IP version 6 (IPv6),” September 2007.).

L-12:

The IPv6 CE router MUST support providing DNS information in the DHCPv6 DNS_SERVERS option [RFC3646] (Droms, R., “DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” December 2003.).

L-13:

The IPv6 CE router SHOULD make available a subset of DHCPv6 options (as listed in section 5.3 of [RFC3736] (Droms, R., “Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6,” April 2004.)) received from the DHCPv6 client on its WAN interface to its LAN side DHCPv6 server.

L-14:

If the delegated prefix changes, i.e. the current prefix is replaced with a new prefix without any overlapping time period, then the IPv6 CE router MUST immediately advertise the old prefix with a preferred lifetime of 0 and a valid lifetime of 2 hours (which must be decremented in real time) in a Router Advertisement message.

L-15:

The IPv6 CE router MUST send an ICMP Destination Unreachable Message, code 5 (Source address failed ingress/egress policy) for packets forwarded to it using an address from a prefix which has been deprecated.

4.4.  Security Considerations

It is considered a best practice to filter obviously malicious traffic (e.g. spoofed packets, "martian" addresses, etc.). Thus, the IPv6 CE router should support basic stateless egress and ingress filters. The CE router should also offer mechanisms to filter traffic entering the customer network; however, the method by which vendors implement configurable packet filtering is beyond the scope of this document.

Security requirements:

S-1:

The IPv6 CE router SHOULD support [I‑D.ietf‑v6ops‑cpe‑simple‑security] (Woodyatt, J., “Recommended Simple Security Capabilities in Customer Premises Equipment for Providing Residential IPv6 Internet Service,” April 2010.).

S-2:

The IPv6 CE router MUST support ingress filtering in accordance with [RFC2827] (Ferguson, P. and D. Senie, “Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing,” May 2000.)(BCP 38)

5.  Acknowledgements

Thanks to the following people (in alphabetical order) for their guidance and feedback:

Mikael Abrahamsson, Merete Asak, Scott Beuker, Mohamed Boucadair, Rex Bullinger, Brian Carpenter, Remi Denis-Courmont, Gert Doering, Alain Durand, Katsunori Fukuoka, Tony Hain, Thomas Herbst, Kevin Johns, Stephen Kramer, Victor Kuarsingh, Francois-Xavier Le Bail, David Miles, Shin Miyakawa, Jean-Francois Mule, Michael Newbery, Carlos Pignataro, John Pomeroy, Antonio Querubin, Teemu Savolainen, Matt Schmitt, Hiroki Sato, Mark Townsley, Bernie Volz, James Woodyatt, Dan Wing and Cor Zwart

This draft is based in part on CableLabs' eRouter specification. The authors wish to acknowledge the additional contributors from the eRouter team:

Ben Bekele, Amol Bhagwat, Ralph Brown, Eduardo Cardona, Margo Dolas, Toerless Eckert, Doc Evans, Roger Fish, Michelle Kuska, Diego Mazzola, John McQueen, Harsh Parandekar, Michael Patrick, Saifur Rahman, Lakshmi Raman, Ryan Ross, Ron da Silva, Madhu Sudan, Dan Torbet and Greg White

6.  Contributors

The following people have participated as co-authors or provided substantial contributions to this document: Ralph Droms, Kirk Erichsen, Fred Baker, Jason Weil, Lee Howard, Jean-Francois Tremblay, Yiu Lee, John Jason Brzozowski and Heather Kirksey.

7.  IANA Considerations

This memo includes no request to IANA.

8.  References

8.1. Normative References

8.2. Informative References

Authors' Addresses