Network Working Group J. Bound
Internet-Draft Compaq Computer Corporation
Expires: July 2, 2002 M. Carney
Sun Microsystems, Inc.
C. Perkins
Nokia Research Center
T. Lemon
Nominum
B. Volz
Ericsson
R. Droms
Cisco Systems
Jan 2002
DNS Configuration Options for DHCPv6
draft-ietf-dhc-dhcpv6-opt-dnsconfig-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on July 2, 2002.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document describes three options for DNS-related configuration
information in DHCPv6: DNS Servers, Domain Name, Domain Search list.
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1. Introduction
This document describes three options for configuration information
related to Domain Name Service (DNS) [1, 2] in DHCPv6 [5].
2. Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in RFC 2119 [1]
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 [3]. The DNS servers SHOULD be 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
option-length: Length of the 'options' field in octets; must be a
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multiple of 16
DNS server: IP address of DNS server
5. Domain Name option
The Domain Name option is used by the server to inform the client of
the domain name the client should append to its host name to form the
client's fully qualified domain name (FQDN).
The format of the Domain Name 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_NAME | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| domain-name |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_DOMAIN_NAME (tbd)
option-length: Length of the 'domain-name' field in octets
domain-name: Domain name for client
The 'domain-name' MUST be encoded as specified in section
"Representation and use of domain names" of the DHCPv6 specification
[5].
Local client policy MAY choose to override the domain-name supplied
in the Domain-Name option with a locally configured value.
6. Domain Search List option
In some circumstances, it is useful for the DHCP client to be
configured with list of domain names to be appended to a host name
when resolving DNS name. This document defines a new DHCP option
which is passed from the DHCP server to the DHCP client to specify
the domain search list used when resolving hostnames with DNS. This
option does not apply to other name resolution mechanisms.
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The format of the Domain Search 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 [5].
Local client policy MAY choose to override the domain search list
supplied in the Domain Search List option with a locally configured
value.
7. Appearance of these option
The Domain Name Server option MUST appear only in the following
messages: Solicit, Advertise, Request, Confirm, Renew, Rebind,
Information-Request, Reply.
The Domain Name 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. Note that the Domain Search List option
will only appear in a Solicit message if the client has a preferred
search list that it is supplying to the server as a hint.
8. 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.
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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 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 and the Domain
Name option, the DHCP client SHOULD use authenticated DHCP (see
section "Authentication of DHCP messages" in the DHCPv6 specification
[5].
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 [4], DHCP clients and servers MUST use
authenticated DHCP when a Domain Search List option is included in a
DHCP message.
9. 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 [5].
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.
[3] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[4] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[5] 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.
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Authors' Addresses
Jim Bound
Compaq Computer Corporation
ZK3-3/W20
110 Spit Brook Road
Nashua, NH 03062-2698
USA
Phone: +1 603 884 0062
EMail: Jim.Bound@compaq.com
Mike Carney
Sun Microsystems, Inc.
Mail Stop: UMPK17-202
901 San Antonio Road
Palo Alto, CA 94303-4900
USA>
Phone: +1 650 786 4171
EMail: mwc@eng.sun.com
Charlie Perkins
Nokia Research Center
Communications Systems Lab
313 Fairchild Drive
Mountain View, CA 94043
USA
Phone: +1 650 625 2503
EMail: charliep@iprg.nokia.com
Nominum
EMail: mellon@nominum.com
Bernie Volz
Ericsson
959 Concord Street
Framingham, MA 01701
USA
Phone: +1 508 875 3162
EMail: bernie.volz@ericsson.com
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Ralph Droms
Cisco Systems
250 Apollo Drive
Chelmsford, MA 01824
USA
Phone: +1 978 497 4733
EMail: rdroms@cisco.com
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