DHC Working Group E. Bi Internet-draft S. Manning Intended Status: Standards Track M. Wong Expires: Janurary 17, 2013 Y. Cui Huawei July 16, 2012 Security option extensions for DHCP draft-bi-dhc-sec-option-02 Abstract This document defines a new option that can be used by DHCP servers to provision with DHCP clients specific security configuration information. It has been known that DHCP protocol typically works at the very beginning stage of the access to networks, thus lack of security protection. However, although it is difficult to set up some security mechanism for DHCP protocol solely, it is able to play a key role for DHCP server to provide configuration information to help building security mechanism within those pre-configured DHCP clients and devices. This new option defines a simple extension to current standard format and benefits to those who need to activate security mechanism in an early stage and interoperate within devices from multiple vendors. 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Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Applicability . . . . . . . . . . . . . . . . . . . . . . . 3 2 Terminology Used in This Document . . . . . . . . . . . . . . . 4 3 DHCP Security Specific Configuration Option . . . . . . . . . . 4 4 Security Considerations . . . . . . . . . . . . . . . . . . . . 6 5 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 7 References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1 Normative References . . . . . . . . . . . . . . . . . . . 6 7.2 Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 E. Bi et al. Expires January 17, 2012 [Page 2] Internet draft DHCP security options extensions July 2012 1 Introduction DHCP provides a framework for passing network configuration information to hosts on a TCP/IP network. Some configuration parameters and control information can be carried in DHCP options which are defined in [RFC2132], [RFC3046], [RFC3118], [RFC4030], etc. When a host that acts as a DHCP client booting up, it can be configured with some security policy. Such as, due to the security concern, all the IP packets to and from a client may be required to be protected by a secure mechanism, which is typically an IPsec channel or transport layer security established with the server or administrator. These security mechanisms require the configuration information can be provisioned to the DHCP client at the early stage when it is connected to the network. In particular, the DHCP client should be notified the crucial security configuration information as early as possible. DHCP is essential for users who want to connect to IP networks before they can communicate with other hosts. Among a number of indispensable Internet protocols, it provides the most convenient way to make configuration extension, which eliminates the manual task by a network administrator and duplicate resource assignments. Thus, in addition to the essential IP address and network boot servers, security configuration information is expected to be included in DHCP extension, as well. 1.1 Applicability Some scenarios that require this kind of provisioning secure configuration information are when DHCP clients in wireless base stations are attaching to a wireless network infrastructure. As defined in [3GPP.33.310], for establishing security link with operator's network, wireless base station shall connect to the PKI server and SeGW. If secure configuration information (address of PKI server, address of SeGW, etc.) is unavailable on the wireless base stations, the wireless base stations cannot connect to the network. So it is important for the host to obtain a set of security configuration information, which is configured in the DHCP server prior to the establishment of the security tunnel. Currently, some implementations exchange this security information through DHCP vendor-specific options, i.e. OPTION 43. However, this has the usual limitations of requiring the client and server to understand these vendor-specific extensions. Since most of the security configuration information are common across most clients and servers, having a standardized set of options and procedures would be a huge benefit to interoperability. This document defines a new security DHCP option used to exchange the security configuration information. E. Bi et al. Expires January 17, 2012 [Page 3] Internet draft DHCP security options extensions July 2012 The newly defined option is as follows: Option: DHCP security specific configuration option 2 Terminology Used in This Document 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 [RFC2119]. 3 DHCP Security Specific Configuration Option A DHCP server can use this option to indicate to the DHCP client specific configuration information, such as the address of the security gateway that is used to establish IPsec tunnel within the enterprise network, the address of the PKI server which is used to issue certificate to the DHCP client. This option may be used wherever DHCP options are available, as specified in [RFC2131] and [RFC2132]. It is most meaningful in the messages between DHCP client and DHCP server, such as, DHCPOFFER and DHCPACK. The format of the option is as follows: Opt-ID | opt-length | attribute 1 | attribute 2| ...... where Opt-ID denotes the new option ID, opt-length denotes the bit length of following attributes, and attributes 1,2... can be extended correspondingly to various use cases. For example, in the above use case of 3GPP standards [3GPP.33.310], the addresses (IP or FQDN) of Se-GW and PKI server are needed to know for DHCP client (wireless base station), the DHCP option could be as follows, where attributes 1 and 2 denote Se-GW and PKI server, respectively. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attribute 1 | data-len1 | Security-GW ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Security-GW IP Address Data | / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attribute 2 | data-len2 | PKI Server ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + PKI Server IP Address Data | / / E. Bi et al. Expires January 17, 2012 [Page 4] Internet draft DHCP security options extensions July 2012 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | other attributes | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. The format of DHCP security specific configuration option This option contains the information corresponding to one or more security-specific code number. Multiple instances of this option may be present and must be concatenated in accordance with [RFC3396]. The definition of the information carried in this option is defined uniformly. The security-specific attribute information indicated the security information type. For example, a DHCP client indicates security configuration information with the same code number that can be interpreted by different DHCP servers. As the security-specific code is uniform and standard, no ambiguity interpretation can occur. A security-specific code number is unique and only occur once in the option and should be treated independently. This option can also contains one or more encapsulated options that defined in [RFC4361]. DHCP client can request the configuration information from DHCP server by sending DHCP request message. DHCP server allocates the configuration information to DHCP client according to the client ID. i.e., DHCP server can know whether this connecting client needs to be configured by client ID, which can be carried in option 60 specified in [RFC4361]. If the security configuration information is needed, the defined security-specific option will be sent back to the client from DHCP server in DHCPOFFER. If this option is used, different DHCP clients implemented by different vendors have good interoperability. The DHCP server needs only to support one standardized format which reduces complexity and enhances performance. If the DHCP client is configured with a security policy, all of the attributes listed in the figure MUST be carried in the newly defined option in DHCPDISCOVER or DHCPREQUESTmessages. And DHCP server MUST allocate all the requested configuration attributes according to the received attribute type and format in the DHCP response messages. Use of security-specific information allows enhanced operation, utilizing additional features in a DHCP implementation. Servers not equipped to interpret the security-specific information sent by a client MUST ignore it. Clients that do not receive desired security- specific information MUST ignore it and initiate another DHCP operation. Finally, it is also desired to extend this option to IPv6, which is left to be improved. E. Bi et al. Expires January 17, 2012 [Page 5] Internet draft DHCP security options extensions July 2012 4 Security Considerations This document defines a new security option used by DHCP servers and DHCP clients to provision security configuration information. However, the security mechanism itself does not need to rely on the security of DHCP, i.e. the configuration information provided by DHCP server can hardly guarantee their own validity, since DHCP originally is lack of protection. Therefore, the new option proposed in this document is not aimed to solve the security of DHCP, but try to make use of DHCP to provide configuration information for those who have already equipped with security mechanism, and that security cannot be harmed by potentially invalid information provisioned. 5 IANA Considerations There may be IANA consideration for taking additional value for the option. The value of the protocol field needed to be assigned from the numbering space. 6 Acknowledgements Thanks to Eric Chen, Xiangsong Cui and Rock Xie who contributed actively to this document. 7 References 7.1 Normative References [RFC2119] 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", RFC 2131, March 1997. [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997. [RFC3118] Droms, R., Ed., and W. Arbaugh, Ed., "Authentication for DHCP Messages", RFC 3118, June 2001. [RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers for Dynamic Host Configuration Protocol Version Four (DHCPv4)", RFC 4361, February 2006. E. Bi et al. Expires January 17, 2012 [Page 6] Internet draft DHCP security options extensions July 2012 7.2 Informative References [3GPP.33.310] 3GPP, "Network Domain Security (NDS); Authentication Framework (AF)", 3GPP TS 33.310 10.3.0, June 2011. [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, January 2001. [RFC3396] Lemon, T. and S. Cheshire, "Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396, November 2002. [RFC4030] Stapp, M. and T. Lemon, "The Authentication Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Option", RFC 4030, March 2005. Authors' Addresses Emily Bi Huawei Technologies Beijing, China Email: bixiaoyu@huawei.com Serge Manning Huawei Technologies TX, U.S. Email: serge.manning@huawei.com Marcus Wong NJ, U.S. Huawei Technologies Email: mwong@huawei.com Yang Cui Huawei Technologies Beijing, China Email: cuiyang@huawei.com E. Bi et al. Expires January 17, 2012 [Page 7]