DHCPv4 over A+P softwires
Author(s): Ole Troan
A node getting IPv4 access via an A+P mechanism might need other IPv4 configuration information. This memo describes how DHCPv4 is supported, on IPv4 over IPv6 tunnels with shared IPv4 addresses....
DHC working Group O. Troan Internet-Draft Cisco Systems Intended status: Informational June 12, 2013 Expires: December 14, 2013 DHCPv4 over A+P softwires draft-troan-dhc-dhcpv4osw-00 Abstract A node getting IPv4 access via an A+P mechanism might need other IPv4 configuration information. This memo describes how DHCPv4 is supported, on IPv4 over IPv6 tunnels with shared IPv4 addresses. 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 December 14, 2013. Copyright Notice Copyright (c) 2013 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 . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Troan Expires December 14, 2013 [Page 1] Internet-Draft June 2013 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 5. Security Considerations . . . . . . . . . . . . . . . . . . . 3 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 3 7. Normative References . . . . . . . . . . . . . . . . . . . . . 3 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction A router connected to a IPv6 only network might get IPv4 connectivity through an IPv4 over IPv6 tunnel. The router can be provisioned with a single IPv4 address, a shared IPv4 address or an IPv4 prefix. The tunnel provisioining mechanism may include provisioning of the IPv4 address/prefix and optional port set, or the IPv4 address may be provisioned using DHCPv4 running over the tunnel. Even though the addresses are provisioned as part of tunnel setup, there might be other IPv4 configuration parameters that should be provisioned to the host. This memo describes how DHCPv4 can be supported over an IPv4 over IPv6 tunnel. The mechanism is named "DHCPv4 over softwire" as described here [I-D.ietf-dhc-v4configuration]. MAP [I-D.ietf-softwire-map] is used as the example of the IPv4 over IPv6 tunnel mechanism in this memo, while the mechanism described here should equally apply to other IPv4 over IPv6 mechanisms. Issues with running DHCPv4 over a softwire: 1. A DHCPv4 without an IPv4 address sends requests from the unspecified address (0.0.0.0) the the IPv4 broadcast address (255.255.255.255). 2. DHCPv4 clients send packets with UDP port 67 to UDP port 68 (server). 3. DHCPv4 uses hardware addresses (read Ethernet MAC addresses) as the way to identify clients. In MAP all nodes have a point to point tunnel to the MAP Border Relay (BR). The MAP BR is responsible for connecting the MAP domain with the IPv4 Internet. Given that the MAP Customer Edge (CE) router has a point to point tunnel to the MAP BR, then that tunnel supports broadcast already. The MAP BR MUST either be a DHCPv4 relay or DHCPv4 server. If the MAP BR is operating as a relay, it must insert option 82, with the DHCPv4 clients source IPv6 address. The DHCPv4 client and server MUST support [RFC4361] and [RFC6842]. The client identifier is used instead of a hardware identifier. A MAP BR does not consider the unspecified IPv4 address as a shared IPv4 address. Or more correctly all MAP CEs can use the unspecified IPv4 address with the full port set. The MAP BR routes IPv4 packets using the option 82, just like any other DHCPv4 relay. Troan Expires December 14, 2013 [Page 2] Internet-Draft June 2013 A DHCPv4 client that has its IPv4 address provisioned using the tunnel setup mechanism, MAY send DHCPINFORMs using it's IPv4 unicast address. In the case that this address is port restricted, a UDP port within the assigned range MUST be used instead of port 67. A DHCPv4 client communicates directly with the DHCPv4 server after it has acquired addresses. That requires that the DHCPv4 server supports clients using a different UDP port than 68. If DHCPv4 is to be used for also assigning a port range, a new DHCPv4 option is required. The tunnel provisioning mechanism SHOULD indicate if DHCPv4 is required on the link or not. For links without a provisioning mechanism, e.g. a manually configured tunnel, DHCPv4 SHOULD always be tried. 2. Architecture IPv4 over IPv6 o---------------o tunnel o-------------o o-------o | DHCPv4 client |________________| MAP BR |____| DHCPv4| | MAP CE |----------------| DHCPv4 relay| | server| o---------------o o-------------o o-------o Figure 1: DHCP 3. Summary This is a simple mechanism that requires a minimum of changes to existing implementations and deployment practice. The mechanism requires port aware DHCPv4 clients and servers. That is, that the client can use a different UDP port than 68. There is already some support for that in the ISC DHCP implementation. In addition the DHCPv4 relay must be aware of the link-layer type, and insert a correct option-82, just like it does today for VLANs. 4. IANA Considerations This specification does not require any IANA actions. 5. Security Considerations 6. Acknowledgements 7. Normative References [I-D.ietf-dhc-v4configuration] Troan Expires December 14, 2013 [Page 3] Internet-Draft June 2013 Rajtar, B. and I. Farrer, "Provisioning IPv4 Configuration Over IPv6 Only Networks", draft-ietf-dhc- v4configuration-01 (work in progress), May 2013. [I-D.ietf-softwire-map] Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S., Murakami, T., and T. Taylor, "Mapping of Address and Port with Encapsulation (MAP)", draft-ietf-softwire-map-07 (work in progress), May 2013. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC2119, March 1997. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers for Dynamic Host Configuration Protocol Version Four (DHCPv4)", RFC4361, February 2006. [RFC6842] Swamy, N., Halwasia, G., and P. Jhingran, "Client Identifier Option in DHCP Server Replies", RFC6842, January 2013. Author's Address Ole Troan Cisco Systems Philip Pedersens vei 1 Lysaker 1366 Norway Email: email@example.com Troan Expires December 14, 2013 [Page 4]