Network Working Group R. Droms (ed.) Internet-Draft Cisco Systems Expires: September 30, 2002 Apr 2002 DNS Configuration options for DHCPv6
draft-ietf-dhc-dhcpv6-opt-dnsconfig-01.txtdraft-ietf-dhc-dhcpv6-opt-dnsconfig-02.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 30, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes DHCPv6 options for passing a list of available DNS Servers and a domain search list to a client. 1. Introduction This document describes threetwo options for passing configuration information related to Domain Name Service (DNS) [1, 2] in DHCPv6 . 2. Requirements 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. Terminology This document uses terminology specific to IPv6 and DHCPv6 as defined in section "Terminology" of the DHCP specification. 4. Domain Name Server option The Domain Name Server option provides a list of one or more IP addresses of DNS servers to which a client's DNS resolver MAY send DNS queries . The DNS servers are listed in the order of preference for use by the client resolver. The format of the Domain Name Server option is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_DNS_SERVERS | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | DNS-server (IP address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | DNS-server (IP address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code: OPTION_DNS_SERVERS (tbd) option-length: Length of the 'options' field in octets; must be a multiple of 16 DNS-server: IP address of DNS server 5. Domain Search List option A server sends a Domain Search List option to the DHCP client to specify the domain search list the client is to use when resolving hostnames with DNS. This option does not apply to other name resolution mechanisms. The format of the Domain Search List option is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_DOMAIN_LIST | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | searchstring | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code: OPTION_DOMAIN_LIST (tbd) option-length: Length of the 'searchstring' field in octets searchstring: The specification of the list of domain names in the Domain Search List The list of domain names in the 'searchstring' MUST be encoded as specified in section "Representation and use of domain names" of the DHCPv6 specification . 6. Appearance of these options The Domain Name Server option MUST appear only in the following messages: Solicit, Advertise, Request, Confirm, Renew, Rebind, Information-Request, ReplyReply. The Domain Search List option MUST appear only in the following messages: Solicit, Advertise, Request, Confirm, Renew, Rebind, Information-Request, ReplyReply. 7. Security Considerations The Domain Name Server option may be used by an intruder DHCP server to cause DHCP clients to send DNS queries to an intruder DNS server. The results of these misdirected DNS queries may be used to spoof DNS names. The Domain Name option may be used by an intruder DHCP server to configure a DHCP client with an invalid domain name, which could be used as a denial of service attack. The DomainSearch List option may be used by an intruder DHCP server to cause DHCP clients to search through invalid domains for incompletely specified domain names. The results of these misdirected searches may be used to spoof DNS names. To avoid attacks through the Domain Name Server option and the Domain Nameoption, the DHCP client SHOULD use authenticated DHCP (see section "Authentication of DHCP messages" in the DHCPv6 specification). Because the Domain Search List option may be used to spoof DNS name resolution in a way that cannot be detected by DNS security mechanisms like DNSSEC , DHCP clients and servers MUST use authenticated DHCP when a Domain Search List option is included in a DHCP message. 8. IANA Considerations IANA is requested to assign an option code to these options from the option-code space defined in section "DHCPv6 Options" of the DHCPv6 specification . References  Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987.  Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R. Droms (ed.), "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-23 (work in progress), February 2002.  Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. Author's Address Ralph Droms (ed.) Cisco Systems 250 Apollo Drive Chelmsford, MA 01824 USA Phone: +1 978 497 4733 EMail: firstname.lastname@example.org Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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