draft-ietf-dhc-fqdn-opt-02.txt   draft-ietf-dhc-fqdn-opt-03.txt 
Network Working Group Yakov Rekhter, cisco Systems Network Working Group Yakov Rekhter, cisco Systems
INTERNET DRAFT Ralph Droms, Bucknell University INTERNET DRAFT Ralph Droms, Bucknell University
Obsoletes: draft-ietf-dhc-fqdn-opt-01.txt March 1997 Obsoletes: draft-ietf-dhc-fqdn-opt-02.txt July 1997
Expires September 1997 Expires January 1998
An option for FQDNs in DHCP options An option for FQDNs in DHCP options
<draft-ietf-dhc-fqdn-opt-02.txt> <draft-ietf-dhc-fqdn-opt-03.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
skipping to change at page 1, line 41 skipping to change at page 1, line 41
DHCP [DHCP] can be used to automate the process of configuring TCP/IP DHCP [DHCP] can be used to automate the process of configuring TCP/IP
host computers. However, some of the DHCP options carry IP addresses host computers. However, some of the DHCP options carry IP addresses
rather than Fully Qualified Domain Names (FQDN). Use of IP addresses rather than Fully Qualified Domain Names (FQDN). Use of IP addresses
constrains the DHCP client to use the addresses that were in use at constrains the DHCP client to use the addresses that were in use at
the time the client received its configuration information; these the time the client received its configuration information; these
addresses may change over time, (e.g., a server may be assigned a new addresses may change over time, (e.g., a server may be assigned a new
IP address), so that the IP addresses used by the client may become IP address), so that the IP addresses used by the client may become
invalid. invalid.
An alternative to passing IP addresses is to pass FQDNs instead of An alternative to passing IP addresses is to pass FQDNs instead of
(numeric) IP addresses. Doing this allows to defer binding between a (numeric) IP addresses. Doing this allows a client to defer binding
particular network entity (e.g., a server) and its IP address until between a particular network entity (e.g., a server) and its IP
run time. As stated in [Carpenter:96], "Deferring the binding avoids address until run time. As stated in [Carpenter:96], "Deferring the
the risk of changed mapping between IP addresses and specific network binding avoids the risk of changed mapping between IP addresses and
entities (due to changing addressing information). Moreover, specific network entities (due to changing addressing information).
reliance on FQDNs (rather than IP addresses) also localizes to the Moreover, reliance on FQDNs (rather than IP addresses) also localizes
DNS the changes needed to deal with changing addressing information to the DNS the changes needed to deal with changing addressing
due to renumbering." information due to renumbering."
DRAFT An option for FQDNs in DHCP options March 1997 DRAFT An option for FQDNs in DHCP options July 1997
This document defines a new DHCP option that allows the use of FQDNs This document defines a new DHCP option that allows the use of FQDNs
instead of IP addresses in DHCP options. instead of IP addresses in DHCP options.
1. FQDN Option 1. FQDN Option
The FQDN option allows the use of FQDNs rather than IP addresses in The FQDN option allows the use of FQDNs rather than IP addresses in
DHCP options. The FQDN option contains other DHCP options, which DHCP options. The FQDN option contains other DHCP options, which
then carry FQDNs rather than IP addresses as data. then carry FQDNs rather than IP addresses as data.
The code for the FQDN option is 89. The Len field gives the total The code for the FQDN option is 89. The Len field gives the total
length of all of the DHCP options contained in the FQDN option. The length of all of the DHCP options contained in the FQDN option. The
Code, Len, Subcode and Sublen are all one octet long. The FQDN field Code, Len, Subcode and Sublen are all one octet long. The FQDN field
is variable length. is variable length.
For each subcode carried in the FQDN option, the IP address in the For each subcode carried in the FQDN option, the IP address in the
option represented by the subcode is replaced by a FQDN. option represented by the subcode is replaced by a FQDN.
The Sublen field shall be set to the length (in octets) of the FQDN The Sublen field shall be set to the length (in octets) of the FQDN
carried in the option. The FQDN field carries the FQDN itself. carried in the option; the length specified by the Sublen field does
not include the Subcode and Sublen fields. The FQDN field carries
the FQDN itself.
+----------+----------+ +----------+----------+
| Code | Len | | Code | Len |
+----------+----------+---------+-----------+-------------------- +----------+----------+---------+-----------+--------------------
| Subcode | Sublen | FQDN | Subcode | Sublen | FQDN
+----------+----------+---------+-----------+-------------------- +----------+----------+---------+-----------+--------------------
.................. ..................
+----------+----------+---------+-----------+-------------------- +----------+----------+---------+-----------+--------------------
| Subcode | Sublen | FQDN | Subcode | Sublen | FQDN
+----------+----------+---------+-----------+-------------------- +----------+----------+---------+-----------+--------------------
1.1 DHCP options containing a list of parameters 1.1 DHCP options containing a list of parameters
More that one triple with a given subcode may appear within a single More than one triple with a given subcode may appear within a single
FQDN option. The FQDNs contained in triples with the same subcode FQDN option. The FQDNs contained in triples with the same subcode
should be treated as a list of parameters for the DHCP option should be treated as a list of parameters for the DHCP option
represented by the subcode. represented by the subcode.
Because FQDNs are variable length, lists of FQDNs cannot be encoded Because FQDNs are variable length, lists of FQDNs cannot be encoded
in DHCP options within the FQDN option. DHCP Options that can carry in DHCP options within the FQDN option. DHCP Options that can carry
a list of IP addresses should be coded as multiple subcodes in the a list of IP addresses should be coded as multiple subcodes in the
FQDN option, to differentiate among the variable-length FQDNs.
DRAFT An option for FQDNs in DHCP options March 1997 DRAFT An option for FQDNs in DHCP options July 1997
FQDN option, to differentiate among the variable-length FQDNs. If
the order of the IP addresses in the option identified by the subcode
was meaningful, e.g., representing a priority or preference order,
the order retains that same meaning in multiple instances of the same
subcode in the FQDN option. DHCP options that carry pairs of IP
addresses, e.g., the static route option (code 33), MUST NOT be
encoded in the FQDN option.
This option only allows the use of FQDNs for options that have been This option only allows the use of FQDNs for options that have been
elsewhere defined to carry IP addresses. elsewhere defined to carry IP addresses. If the FQDN option is used,
the DNS server option (code 6) SHOULD be specified before any FQDN
options, and the client's protocol software MUST initialize its DNS
resolver with that DNS server address before resolving any FQDNs in
subsequent options. Not all DHCP options that specify IP addresses
may be sensibly transmitted as FQDNs; for example, options that
specify an IP address-subnet mask pair MUST NOT be encoded in the
FQDN option. The DNS server option SHOULD NOT be encoded in the FQDN
option because, under most circumstances, the FQDN of a DNS server
cannot be resolved until the IP address fo a server is available.
The router option SHOULD NOT be encoded as an FQDN because queries to
the DNS server may require that the client's protocol software be
initialized with the router's IP address; e.g., the DNS server may be
on a different subnet.
1.2 Example 1.2 Example
The following illustrates how the FQDN option could be used to carry The following illustrates how the FQDN option could be used to carry
FQDNs for 2 LPR Servers with FQDNs lpr1.xxx.org and lpr2.yy.org, and FQDNs for 2 LPR Servers with FQDNs lpr1.xxx.org and lpr2.yy.org, and
one Network Information Server with FQDN nis.zzzz.org. one Network Information Server with FQDN nis.zzzz.org.
+---+---+ +---+---+
|xx |41 | |89 |41 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|41 |12 | n | i | s | . | z | z | z | z | . | o | r | g | |41 |12 | n | i | s | . | z | z | z | z | . | o | r | g |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 9 |12 | l | p | r | 1 | . | x | x | x | . | o | r | g | | 9 |12 | l | p | r | 1 | . | x | x | x | . | o | r | g |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 9 |11 | l | p | r | 2 | . | y | y | . | o | r | g | | 9 |11 | l | p | r | 2 | . | y | y | . | o | r | g |
+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+
2. Security Considerations 2. Security Considerations
Security issues are not discussed in this document. DHCP currently provides no authentication or security mechanisms.
Potential exposures to attack are discussed in section 7 of the DHCP
protocol specification [1].
DRAFT An option for FQDNs in DHCP options July 1997
The DHCP FQDN option introduces DNS into the client configuration
process, so that compromises to the DNS system may compromise the
security of client configuration.
3. References 3. References
[Carpenter:96] Carpenter, B., Rekhter, Y., "Renumbering needs work", [Carpenter:96] Carpenter, B., Rekhter, Y., "Renumbering needs work",
RFC1900, February 1996. RFC1900, February 1996.
[DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC1541, [DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC2131,
October 1993. March 1997.
4. Acknowledgments 4. Acknowledgments
The authors gratefully acknowledge the input and review of the The authors gratefully acknowledge the input and review of the
Dynamic Host Configuration working group. They also thank cisco Dynamic Host Configuration working group. They also thank cisco
Systems and Bucknell University for their support in the development Systems and Bucknell University for their support in the development
of this document. of this document.
DRAFT An option for FQDNs in DHCP options March 1997
5. Author Information 5. Author Information
Yakov Rekhter Yakov Rekhter
cisco Systems, Inc. cisco Systems, Inc.
170 Tasman Dr. 170 Tasman Dr.
San Jose, CA 95134 San Jose, CA 95134
Phone: (914) 528-0090 Phone: (914) 528-0090
email: yakov@cisco.com email: yakov@cisco.com
 End of changes. 

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