draft-ietf-dhc-nsso-04.txt   rfc2937.txt 
Network Working Group C. Smith Network Working Group C. Smith
Internet Draft Sun Microsystems, Inc. Request for Comments: 2937 Sun Microsystems, Inc.
June 2000 Category: Standards Track September 2000
Expires December 2000
The Name Service Search Option for DHCP The Name Service Search Option for DHCP
<draft-ietf-dhc-nsso-04.txt>
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Abstract Abstract
This document defines a new DHCP option which is passed from the DHCP This document defines a new Dynamic Host Configuration Protocol
Server to the DHCP Client to specify the order in which name services (DHCP) option which is passed from the DHCP Server to the DHCP Client
should be consulted when resolving hostnames and other information. to specify the order in which name services should be consulted when
resolving hostnames and other information.
Introduction Introduction
The Dynamic Host Configuration Protocol (DHCP)[1] provides a The Dynamic Host Configuration Protocol (DHCP)[1] provides a
framework for passing configuration information to hosts on a TCP/IP framework for passing configuration information to hosts on a TCP/IP
network. RFC 2132 [2] allows DHCP servers to specify configuration network. RFC 2132 [2] allows DHCP servers to specify configuration
information for various kinds of name services to be passed to DHCP information for various kinds of name services to be passed to DHCP
clients. Many clients use multiple name services and have crafted clients. Many clients use multiple name services and have crafted
their own conventions that allow an individual host to express the their own conventions that allow an individual host to express the
order among the various name services with which lookups are done. order among the various name services with which lookups are done.
However, no search order can be specified via DHCP. The purpose of However, no search order can be specified via DHCP. The purpose of
this document is to allow DHCP servers to specify the search order to this document is to allow DHCP servers to specify the search order to
be used by DHCP clients. To avoid the need for inventing and be used by DHCP clients. To avoid the need for inventing and
maintaining a separate name space for this option, we rely on the maintaining a separate name space for this option, we rely on the
existence of previously-defined DHCP options that specify the IP existence of previously-defined DHCP options that specify the IP
address(es) of servers which provide name services whose order we address(es) of servers which provide name services whose order we
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"DHCP client" "DHCP client"
DHCP client or "client" is an Internet host using DHCP to DHCP client or "client" is an Internet host using DHCP to
obtain configuration parameters such as a network address. obtain configuration parameters such as a network address.
"DHCP server" "DHCP server"
A DHCP server or "server" is an Internet host that returns A DHCP server or "server" is an Internet host that returns
configuration parameters to DHCP clients. configuration parameters to DHCP clients.
Name Service Search Option Format Name Service Search Option Format
The code for this option is TBD, and its minimum length is 2 bytes. The code for this option is 117, and its minimum length is 2 bytes.
A DHCP server SHOULD return, in its preferred order, the 16-bit, A DHCP server SHOULD return, in its preferred order, the 16-bit,
network byte order (big-endian [4]) integer option code for the name network byte order (big-endian [4]) integer option code for the
services (the earlier in the list, the more preferred the name name services (the earlier in the list, the more preferred the name
service). service).
Code Length Name Service Search Order in Sequence Code Length Name Service Search Order in Sequence
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD | Len | ns1 | | 117 | Len | ns1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ns2 | ... | | ns2 | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the above diagram, ns1 and ns2 are 16-bit integers corresponding In the above diagram, ns1 and ns2 are 16-bit integers corresponding
to two DHCP options which specify the IP addresses of two different to two DHCP options which specify the IP addresses of two different
types of name server. The current list of name services and their types of name server. The current list of name services and their
DHCP option codes, taken from RFC 2132, includes DHCP option codes, taken from RFC 2132, includes
Name Service Value Name Service Value
Domain Name Server Option 6 Domain Name Server Option 6
Network Information Servers Option 41 Network Information Servers Option 41
NetBIOS over TCP/IP Name Server Option 44 NetBIOS over TCP/IP Name Server Option 44
Network Information Service+ Servers Option 65 Network Information Service+ Servers Option 65
A name service option code of 0 is used to indicate that the
A name service option code of 0 is used to indicate that the client should refer to local naming information (e.g., an
client should refer to local naming information (e.g. an
/etc/hosts file on a UNIX machine). /etc/hosts file on a UNIX machine).
A DHCP server wishing to express that a client should first search A DHCP server wishing to express that a client should first search
DNS, then NIS+, would send DNS, then NIS+, would send
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD | 4 | 6 | | 117 | 4 | 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 65 | | 65 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
DHCP Client Behavior DHCP Client Behavior
The DHCP client will use this option to create a search list for name The DHCP client will use this option to create a search list for
resolution. The client SHOULD ignore any name services appearing in name resolution. The client may receive name services in this
this option that it does not support or has not been configured to option that it does not support or has not been configured to
access. Clients will interpret this option in a system-specific access. Likewise, a client may receive an option that lists name
manner whose specification is outside the scope of this document. services for which no corresponding DHCP option was supplied.
Clients will interpret this option in a system-specific manner
whose specification is outside the scope of this document.
Security Considerations Security Considerations
DHCP currently provides no authentication or security mechanisms. DHCP currently provides no authentication or security mechanisms.
Potential exposures to attack are discussed in section 7 of the DHCP Potential exposures to attack are discussed in section 7 of the DHCP
protocol specification [1]. protocol specification [1].
IANA Considerations IANA Considerations
IANA has assigned a value of TBD for the DHCP option code described IANA has assigned a value of 117 for the DHCP option code described
in this document. in this document.
References References
[1] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March [1] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March
1997. 1997.
[2] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997. [2] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[3] Bradner, S., "Key words for use in RFCs to indicate requirement [3] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997. levels", BCP 14, RFC 2119, March 1997.
[4] Cohen, D., "On Holy Wars and a Plea for Peace", Computer, IEEE, [4] Cohen, D., "On Holy Wars and a Plea for Peace", Computer, IEEE,
October 1981. October 1981.
Author Information Author's Address
Carl Smith Carl Smith
Sun Microsystems, Inc. Sun Microsystems, Inc.
901 San Antonio Road 901 San Antonio Road
Palo Alto, CA 94043 Palo Alto, CA 94043
email: cs@Eng.Sun.COM
Expiration
This document will expire on December 15, 2000. EMail: cs@Eng.Sun.COM
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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