Network Working Group R. Droms (ed.)
Internet-Draft Cisco Systems
Expires: April 24, 2003 October 24, 2002
DNS Configuration options for DHCPv6
draft-ietf-dhc-dhcpv6-opt-dnsconfig-02.txt
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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 two options for passing configuration
information related to Domain Name Service (DNS) [1, 2] in DHCPv6
[4].
2. Requirements
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
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SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be
interpreted as described in RFC2119 [3].
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 [2]. 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
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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 [4].
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, Reply.
The Domain Search List option MUST appear only in the following
messages: Solicit, Advertise, Request, Confirm, Renew, Rebind,
Information-Request, Reply.
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.
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The Domain Search 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, 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 [5], 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 [4].
References
[1] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.
[2] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] 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.
[5] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
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Author's Address
Ralph Droms (ed.)
Cisco Systems
250 Apollo Drive
Chelmsford, MA 01824
USA
Phone: +1 978 497 4733
EMail: rdroms@cisco.com
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Internet-Draft DNS Configuration Options for DHCPv6 October 2002
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