The DHCPv4 Relay Agent Identifier Suboption
Author(s): Mark Stapp, D.T.V. Rao, Bharat Joshi
This document defines a new Relay Agent Identifier suboption for the Dynamic Host Configuration Protocol's (DHCP) Relay Agent Information option. The suboption carries a value that uniquely identifies the relay agent device within the administrative domain. The value...
DHC B. Joshi Internet-Draft D. Ramakrishna Rao Intended status: Standards Track Infosys Ltd. Expires: August 23, 2013 M. Stapp Cisco Systems, Inc. February 19, 2013 The DHCPv4 Relay Agent Identifier Suboption draft-ietf-dhc-relay-id-suboption-13.txt Abstract This document defines a new Relay Agent Identifier suboption for the Dynamic Host Configuration Protocol's (DHCP) Relay Agent Information option. The suboption carries a value that uniquely identifies the relay agent device within the administrative domain. The value is normally administratively-configured in the relay agent. The suboption allows a DHCP relay agent to include the identifier in the DHCP messages it sends. 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 August 23, 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 Joshi, et al. Expires August 23, 2013 [Page 1] Internet-Draft The Relay Agent Id Suboption February 2013 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Example Use-Cases . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Bulk Leasequery . . . . . . . . . . . . . . . . . . . . . . 3 3.2. Industrial Ethernet . . . . . . . . . . . . . . . . . . . . 3 4. Suboption Format . . . . . . . . . . . . . . . . . . . . . . . 4 5. Identifier Stability . . . . . . . . . . . . . . . . . . . . . 4 5.1. Identifier Uniqueness . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6.1. Forged Relay ID attacks . . . . . . . . . . . . . . . . . . 6 6.2. Factory Floor Scenario . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Joshi, et al. Expires August 23, 2013 [Page 2] Internet-Draft The Relay Agent Id Suboption February 2013 1. Introduction The Dynamic Host Configuration Protocol for IPv4 (DHCPv4) [RFC2131] provides IP addresses and configuration information for IPv4 clients. It includes a relay agent capability, in which network elements receive broadcast messages from clients and forward them to DHCP servers as unicast messages. In many network environments, relay agents add information to the DHCP messages before forwarding them, using the Relay Agent Information option [RFC3046]. Servers that recognize the relay agent information option echo it back in their replies. This specification introduces a Relay Agent Identifier (Relay-Id) suboption for the Relay Agent Information option. The Relay-Id suboption carries a sequence of octets that is intended to uniquely identify the relay agent within the administrative domain. In this document, an administrative domain consist of all DHCP servers and relay agents that communicate with each other. 2. Terminology 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]. DHCPv4 terminology is defined in [RFC2131], and the DHCPv4 Relay Agent Information Option in [RFC3046]. 3. Example Use-Cases 3.1. Bulk Leasequery There has been quite a bit of recent interest in extending the DHCP Leasequery protocol [RFC4388] to accommodate some additional situations. There is a recent document [I-D.ietf-dhc-dhcpv4-bulk-leasequery] proposing a variety of enhancements to the existing Leasequery protocol. The document describes a use-case where a relay agent queries DHCP servers using the Relay Identifier to retrieve all the leases allocated through the relay agent. 3.2. Industrial Ethernet DHCP typically identifies clients based on information in their DHCP messages - such as the Client-Identifier option, or the value of the chaddr field. In some networks, however, the location of a client - Joshi, et al. Expires August 23, 2013 [Page 3] Internet-Draft The Relay Agent Id Suboption February 2013 its point of attachment to the network - is a more useful identifier. In factory-floor networks (commonly called 'Industrial' networks), for example, the role a device plays is often fixed and based on its location. Using manual address configuration is possible (and is common) but it would be beneficial if DHCP configuration could be applied to these networks. One way to provide connection-based identifiers for industrial networks is to have the network elements acting as DHCP relay agents supply information that a DHCP server could use as a client identifier. A straightforward way to form identifier information is to combine something that is unique within the scope of the network element, such as a port/slot value, with something that uniquely identifies that network element, such as a Relay Agent Identifier. 4. Suboption Format Format of the Relay Agent Identifier suboption: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |SUBOPT_RELAY_ID| length | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . . identifier (variable) . . . +---------------------------------------------------------------+ Where: SUBOPT_RELAY_ID [TBA] length the number of octets in the suboption (excluding the suboption ID and length fields); the minimum length is one. identifier the identifying data. 5. Identifier Stability If the relay identifier is to be meaningful it has to be stable. A relay agent SHOULD use a single identifier value consistently. The Joshi, et al. Expires August 23, 2013 [Page 4] Internet-Draft The Relay Agent Id Suboption February 2013 identifier used by a relay device SHOULD be committed to stable storage, unless the relay device can regenerate the value upon reboot. If the relay-id configured in a relay agent is not unique within its administrative domain, resource allocation problems may occur as the DHCP server attempts to allocate the same resource to devices behind two different relay agents. Therefore, relay-id configured in a relay agent MUST be unique within its administrative domain. To aid in ensuring uniqueness of relay-ids, relay agents SHOULD make their relay identifiers visible to their administrators via their user interface, through a log entry, through a MIB field, or through some other mechanism. Implementors of relay agents should note that the identifier needs to be present in all DHCP message types where its value is being used by the DHCP server. The relay agent may not be able to add the Relay Agent Information option to all messages - such as RENEW messages sent as IP unicasts. In some deployments that might mean that the server has to be willing to continue to associate the relay identifier it has last seen with a lease that is being RENEWed. Other deployments may prefer to use the Server Identifier Override suboption [RFC5107] to permit the relay device to insert the Relay Agent Information option into all relayed messages. Handling situations where a relay agent device is replaced is another aspect of stability. One of the use-cases for the relay identifier is to permit a server to associate clients' lease bindings with the relay device connected to the clients. If the relay device is replaced, because it has failed or been upgraded, it may be desirable for the new device to continue to provide the same relay identifier as the old device. Therefore if a relay agent supports relay-id, the relay-id should be administratively configurable. 5.1. Identifier Uniqueness Administrators should take special care to ensure that relay-ids configured in their relay agents are not duplicated. There are a number of strategies that may be used to achieve this. Administrators may use a strategy to configure unique relay-ids. One such strategy is that a relay-id on a relay agent may re-use an existing identifier or set of identifiers that are already guaranteed to be unique (e.g., UUID [RFC4122]). For administrators who are already using a provisioning system to manage their networking infrastructure, it may work to enumerate relay agents on the basis of roles, and then as a second step, assign Joshi, et al. Expires August 23, 2013 [Page 5] Internet-Draft The Relay Agent Id Suboption February 2013 those roles to specific relay agents or groups of relay agents. In such a scenario, when a replacement relay agent is first seen by the DHCP server, this could trigger a configuration event on the provisioning system, and the new relay agent could be assigned to the role of the relay agent it is replacing. In some cases it may be that the DHCP server has configurable event notification, and that a duplicate relay-id would cause some event that could trigger a notification, and that would never happen in any other case. In this scenario, administrators should take advantage of this feature. This is not a perfect solution, because it will not work until such an event occurs. A network management/provisioning system may also be able to collect a full list of all relay agents on the network. It may then notice that more than one device reports the same relay-id. In such a case, the provisioning system could notify the administrator of the fault, which could then be corrected. This is not an exhaustive list of strategies. We suggest an additional strategy in the security considerations section; administrators are also encouraged to consider the specifics of their own network configuration to see if there is some way to detect duplicate relay-ids other than the ones listed here, if none of these will work. 6. Security Considerations 6.1. Forged Relay ID attacks Security issues with the Relay Agent Information option and its use by servers in address assignment are discussed in [RFC3046] and [RFC4030]. The DHCP Relay Agent Information option depends on a trusted relationship between the DHCP relay agent and the DHCP server, as described in Section 5 of RFC3046. While the introduction of fraudulent DHCP relay agent information options can be prevented by a perimeter defense that blocks these options unless the DHCP relay agent is trusted, a deeper defense using the authentication suboption for DHCP relay agent information option [RFC4030] SHOULD be deployed as well. It also helps in avoiding duplication of relay identifiers by malicious entities. However, implementation of authentication suboption for DHCP relay agent information option [RFC4030] is not a must to support relay-id suboption. Joshi, et al. Expires August 23, 2013 [Page 6] Internet-Draft The Relay Agent Id Suboption February 2013 6.2. Factory Floor Scenario One possible use case for the relay-id suboption is the automated configuration of machines on a factory floor. In this situation, various sections of the factory floor might be on their own network links, with a relay agent interposed between those links and the DHCP server. The relay-id of each relay agent might cause special configurations to be downloaded to those devices to control their behavior. If a relay agent was deployed on the factory floor in such a situation, with an incorrect relay-id, there is the potential that devices could be misconfigured in a way that could produce incorrect results, cause physical damage, or even create hazardous conditions for workers. In deployment scenarios like this one, administrators must use some dependable technique to ensure that such misconfigurations do not occur. It is beyond the scope of this document to provide a complete list of such techniques. However, as an example, a relay agent device intended for use in such a scenario could require the use of a hardware token that contains the relay-id, that is physically attached to the installation location of the relay agent device, and that can be connected to and disconnected from the relay agent device without the use of special tools. Such a relay agent device should not be operable when this hardware token is not connected to it: either it should fail because it presents an unknown identifier to the DHCP server, or it should simply refuse to relay DHCP packets until the token is connected to it. A relay agent device that does not provide a clear mitigation strategy for a scenario where misconfiguration could have damaging or hazardous consequences should not be deployed in such a scenario. 7. IANA Considerations We request that IANA assign a new suboption code from the registry of DHCP Agent Sub-Option Codes maintained in http://www.iana.org/assignments/bootp-dhcp-parameters. Relay Agent Identifier Suboption [TBA] Joshi, et al. Expires August 23, 2013 [Page 7] Internet-Draft The Relay Agent Id Suboption February 2013 8. Acknowledgments Thanks to Bernie Volz, David W. Hankins, Pavan Kurapati and Ted Lemon for providing valuable suggestions. 9. References 9.1. Normative References [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC2131, March 1997. [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC3046, January 2001. [RFC4030] Stapp, M. and T. Lemon, "The Authentication Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Option", RFC4030, March 2005. 9.2. Informative References [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC4122, July 2005. [RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration Protocol (DHCP) Leasequery", RFC4388, February 2006. [RFC5107] Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp, "DHCP Server Identifier Override Suboption", RFC5107, February 2008. [I-D.ietf-dhc-dhcpv4-bulk-leasequery] Kinnear, K., Stapp, M., Joshi, B., and N. Russell, "Bulk DHCPv4 Lease Query", draft-ietf-dhc-dhcpv4-bulk-leasequery-07 (work in progress), October 2012. Joshi, et al. Expires August 23, 2013 [Page 8] Internet-Draft The Relay Agent Id Suboption February 2013 Authors' Addresses Bharat Joshi Infosys Ltd. 44 Electronics City, Hosur Road Bangalore 560 100 India Email: firstname.lastname@example.org URI: http://www.infosys.com/ D.T.V Ramakrishna Rao Infosys Ltd. 44 Electronics City, Hosur Road Bangalore 560 100 India Email: email@example.com URI: http://www.infosys.com/ Mark Stapp Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough, MA 01719 USA Phone: +1 978 936 0000 Email: firstname.lastname@example.org Joshi, et al. Expires August 23, 2013 [Page 9]