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Network Working Group                      Senthil K Balasubramanian
Internet-Draft                             Intoto
Expires: September 2005                    Michael Alexander
                                           Gustaf Neumann
                                           Wirtschaftsuniversitaet Wien
                                           April 2005


               DHCP Option for Proxy Server Configuration
                  draft-ietf-dhc-proxyserver-opt-03.txt

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
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   RFC 3668.

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Copyright Notice

   Copyright (C) The Internet Society (2005). All Rights Reserved.

Abstract

   This document defines a new Dynamic Host Configuration Protocol
   (DHCP) option, which can be used to configure the TCP/IP host's Proxy
   Server configuration for standard protocols like HTTP, FTP, NNTP,
   SOCKS, Gopher, SLL and etc.  Proxy Server provides controlled and
   efficient access to the Internet by access control mechanism for
   different types of user requests and caching frequently accessed
   information (Web pages and possibly files that might have been
   downloaded using FTP and other protocols).


1. Terminologies Used


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        DHCP Client: A DHCP [RFC-2131] client is an Internet host that
                uses DHCP to obtain configuration information such as
                network address.



        DHCP Server: A DHCP server [RFC-2131] is an Internet host that
                returns configuration parameters to DHCP clients.

        Proxy Server: In a enterprise network that connects to Internet,
                a proxy server is a server that acts as an intermediary
                between a workstation user and the Internet so that the
                enterprise can ensure security, administrative control,
                and caching service. A Proxy server MAY be associated
                with or part of a gateway server that separates the
                enterprise network from the outside network (Usually
                Internet) and a firewall server that protects the
                enterprise network from outside intrusion.

       RDF:A language (Resource Description Framework [RDF-SYN]) for
                describing properties of web resources.


2. Introduction

   The Dynamic Host Configuration Protocol [RFC-2131] provides a
   framework for passing configuration information to hosts on a TCP/IP
   network.  This document describes a DHCP configuration option that
   can be used to inform a DHCP client, the IP addresses of one or more
   proxy services that are either available to it or that must be used
   in order to access internet services, for example through a coporate
   firewall.

   The following diagram depicts the typical setup providing proxy
   service to clients on a network that is protected by a firewall.

   +---------------------------+                +-----------+
   |                           |                |Remote HTTP|
   |                           |        HTTP    |Server     |
   |  +------------+        +-------------+<--->+-----------+
   |  | Clients    |        |Proxy Server |
   |  | Inside the |<------>|    +        | FTP +-----------+
   |  | Firewall   |        |Firewall     |<--->|Remote FTP |
   |  +------------+        +-------------+     |Server     |
   |                           |  ^             +-----------+
   |                           |  |
   |                           |  |             +-----------+
   +---------------------------+  |  NNTP       |Remote NNTP|
                                  +------------>|Server     |
                                                +-----------+

   The primary use of proxies is to allow access to the World Wide Web
   from within a firewall. A proxy service typically runs on firewall
   machine. It waits for a request from inside the firewall, forwards


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   the request to the remote server outside the firewall, reads the
   response and then sends it back to the client. Usually, all the
   clients use the same proxy within a given network, which helps in
   efficient caching of documents that are requested by a number of
   clients. This behavior makes proxies attractive to clients not
   inside a firewall.


   A proxy server increases the network security and user productivity
   by content filtering and controlling both internal and external
   access to information. Also, it provides several other
   functionalities that are not discussed here.


3. Requirements terminology

   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 [RFC 2119].

4. Proxy Server Configuration Option

   This document defines a new DHCP Option called the Proxy Server
   Configuration Option. The format of the Proxy Server configuration
   option is:

           Code    Len    Proxy Server Configuration Entry
         +-------+------+------+------+------+------+-....-+------+
         |  TBD  |   N  |  e1  |  e2  |  e3  |  e4  |      |  en  |
         +-------+------+------+------+------+------+-....-+------+

   Code is TBD and will be assigned by IANA according to [RFC-2939].
   The length N gives the total number of octets in the Proxy Server
   Configuration entries.


   The Proxy Server Configuration entry normally consists of a
   sequence of Protocol Type (p), len (l), flag (f), IP
   address and port. But it can also be a sequence of Protocol
   Type (p), Len and RDF[RDF-SYN] metadata.

        +--+--+--+--+--+--+--+--+--+
        |p |l | f |IP address|port |
        +--+--+--+--+--+--+--+--+--+

   The Protocol(p) is a two octet integer in network byte order,
   length (l) and flag (f) are one octet each; each IP
   address is four octets, and each port number is a two-octet
   integer encoded in network byte order.

   The protocol type(p) specifies the type of Protocol and MUST be
   one of the following assigned numbers.





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       +-------------------------------+
       | protocol     |       Number   |
       +-------------------------------+
       |   HTTP       |         80     |
       +-------------------------------+
       |   FTP        |         21     |
       +-------------------------------+
       |   NNTP       |         119    |
       +-------------------------------+
       |   Gopher     |         70     |
       +-------------------------------+
       |   SSL        |         TBD    |
       +-------------------------------+
       |   SOCKS      |         1080   |
       +-------------------------------+
       |   WAIS       |         210    |
       +-------------------------------+
       |   IMAP       |         220    |
       +-------------------------------+
       |   RDF        |         TBD    |
       +-------------------------------+

   If the protocol type field is RDF[RDF-SYN], then it MUST be
   followed by len (length of RDF metadata) and the actual RDF
   metadata.

   The length field (l) specifies the length of the Proxy Server
   Configuration entry. If some new protocol is introduced in the
   future and if some version of dhcpclient doesn't support, then
   that particular entry can be ignored and process the following
   Proxy Server Configuration Entry, if any.

   The flag field (f) is by default 0.  Otherwise, it can either
   have "-" or "#".

   If it is "-", then the entry becomes a destination address for
   exclusion from forwarding to the proxy.  If it is "#", then the proxy
   requires authentication.

   In cases where it makes sense to specify more than one proxy server
   for a given protocol, these proxy servers MUST be specified as
   additional IP addresses and ports within the same entry.  The list is
   ordered by precedence, with the most preferred proxy server appearing
   first in the list, andthe least preferred proxy server appearing last
   in the list.  The DHCP client SHOULD honor this ordering.

   More than one Proxy Server Configuration Entries MAY be specified in
   the option.  In that case, the list is ordered by precedence, with
   the most preferred proxy server appearing first in the list, and the
   least preferred proxy server appearing last in the list.  The DHCP
   client SHOULD honor this ordering.





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   The format of the Proxy Server Configuration using Metadata type is:


            p       Len        RDF Metadata for the Proxy
         +-------+------+----------------------------------+
         |  RDF  |  N   |             RDF                  |
         +-------+------+----------------------------------+

   The RDF payload is freeform RDF metadata for describing proxy
   properties.  The length N gives the number of octets in the RDF
   metadata field.

   The following entry specifies the sample format of the RDF Meta
   data field

   HTTP proxy:

   <?xml version="1.0"?>
   <!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
             xmlns:dc="http://purl.org/dc/elements/1.1/">
   <rdf:Description rdf:about="http://http-proxy.duke.edu:8080">
        <dc:title>License Gate Proxy</dc:title>
        <dc:creator>John Doe</dc:creator>
        <dc:publisher>Duke OIT</dc:publisher>
        <dc:subject>Offsite Campus Resource Access Proxy</dc:subject>
        <dc:type>Service</dc:subject>
        <dc:rights>Current Duke faculty, staff, and students</dc:rights>
        <dc:date>2004-06-15</dc:date>
   </rdf:Description>
   </rdf:RDF>

   FTP proxy:

   <?xml version="1.0"?>
   <!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
             xmlns:dc="http://purl.org/dc/elements/1.1/">
   <rdf:Description rdf:about="ftp://ftp-proxy.duke.edu:8080">
        <dc:title>License Gate FTP Proxy</dc:title>
        <dc:creator>John Doe</dc:creator>
        <dc:publisher>Duke OIT</dc:publisher>
        <dc:subject>Offsite Campus Resource Access Proxy</dc:subject>
        <dc:type>Service</dc:subject>
        <dc:rights>Current Duke faculty, staff, and students</dc:rights>
        <dc:date>2004-06-15</dc:date>
   </rdf:Description>
   </rdf:RDF>

   As such there is no minimum length to specify a proxy using RDF
   metadata.  But the minimum sensible statement would be a literal
   description of the proxy (<dc:title>License Gate Proxy</dc:title>)
   giving a total of 418 characters including the overhead.



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   For example, with a description element of 60 characters, an URI of
   80 characters plus a minimum XML/RDF syntax conformation/namespace
   declaration of:

   21 Octets <?xml version="1.0"?>
   70 Octets <!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
   64 Octets <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   45 Octets xmlns:dc="http://purl.org/dc/elements/1.1/">
   109 Octets <rdf:Description rdf:about="..80 characters..">
   81 Octets <dc:title>..60 characters..</dc:title>
   18 Octets </rdf:Description>
   10 Octets </rdf:RDF>

   ,the minimum length would be 418 octes.

5. Option Usage

   The Proxy Server Configuration entries SHOULD not repeat the same
   type of proxy entries. The port MUST be a valid TCP/UDP port.
   If the length of the Proxy Server Configuration Option exceeds the
   maximum permissible within a single option (255 octets), then the
   option MUST be represented in the DHCP message as specified
   in [RFC-3396].

   The following example shows how an RDF version of proxy server
   configuration entry of 400 octets is represented in the option.

    Code     Len   Proto   Len
   +-------+------+------+------+------+------+-....-+------+
   |  TBD  | 255  |  RDF |  253 | RDF Meta Data.............|
   +-------+------+------+------+------+------+-....-+------+
    Code     Len   Proto   Len
   +-------+------+------+------+------+------+-....-+------+
   |  TBD  | 149  |  RDF |  147 | RDF Meta Data.............|
   +-------+------+------+------+------+------+-....-+------+

   The following example shows how the same RDF version of proxy
   server configuration entry of 400 octets is represented in the
   option along with a normal version (p|l|f|IP|port) of proxy
   server configuration entry.

   +---+---+----+-+-+-------------+----+---+---+...-+---+-----+
   |TBD|255|HTTP|7|0|192.168.5.10 |8080|RDF|243| RDF Meta Data|
   +---+---+----+-+-+-------------+----+---+---+...-+---+-----+

   +-------+------+------+------+------+------+-....-+------+
   |  TBD  | 159  |  RDF |  157 | RDF Meta Data.............|
   +-------+------+------+------+------+------+-....-+------+

   More than one RDF type of Proxy Server Configuration Entry MUST
   not be sent in this option. This is because, the RDF Meta Data is
   generally more than 255 octets and always require more than one
   option of this type as per [RFC-3396]. However, more than one proxy
   server configuration (FTP, HTTP, SOCKS) can be specified with the


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   same RDF Meta Data as follows

   HTTP and FTP Proxy

   <?xml version="1.0"?>
   <!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
             xmlns:dc="http://purl.org/dc/elements/1.1/">
   <rdf:Description rdf:about="ftp://ftp-proxy.duke.edu:8080">
        <dc:title>License Gate FTP Proxy</dc:title>
        <dc:creator>John Doe</dc:creator>
        <dc:publisher>Duke OIT</dc:publisher>
        <dc:subject>Offsite Campus Resource Access Proxy</dc:subject>
        <dc:type>Service</dc:subject>
        <dc:rights>Current Duke faculty, staff, and students</dc:rights>
        <dc:date>2004-06-15</dc:date>
   </rdf:Description>
   <rdf:Description rdf:about="http://http-proxy.duke.edu:8080">
        <dc:title>License Gate Proxy</dc:title>
        <dc:creator>John Doe</dc:creator>
        <dc:publisher>Duke OIT</dc:publisher>
        <dc:subject>Offsite Campus Resource Access Proxy</dc:subject>
        <dc:type>Service</dc:subject>
        <dc:rights>Current Duke faculty, staff, and students</dc:rights>
        <dc:date>2004-06-15</dc:date>
   </rdf:Description>
   </rdf:RDF>

6. Security Considerations

   The DHCP Options defined here allow an intruder DHCP server to
   misdirect a client, causing it to access a nonexistent or malicious
   proxy server. This allows for a denial of service or man-in-the-middle
   attack. This is a well known property of the DCHP protocol; this option
   does not create any additional risk of such attacks.

   DHCP provides an authentication mechanism, as described in [RFC-3118],
   which may be used if authentication is required.


7. IANA Considerations

   IANA is requested to assign an option code to the Proxy Server
   Configuration Option and protocol numbers for the SSL and RDF
   protocol.

8. Acknowledgements


   Thanks to the DHC Working Group for their time and input into the
   specification. In particular, thanks to (in alphabetical order)
   Bernie Volz, Ralph Droms, Robert Elz, and Ted Lemon for their
   thorough review.




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9. Normative References

   [RFC-2131]  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
        March 1997.

   [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
        Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC-3396] Lemon, T. and S. Cheshire, "Encoding Long DHCP Options",
        RFC 3396, November 2002.

10. Informative References

   [RFC-3118] Droms, R.  and W.  Arbaugh, "Authentication for DHCP
        Messages", RFC 3118, June 2001.

   [RFC-2939] Droms, R., "Procedures and IANA Guidelines for Definition
         of New DHCP Options and Message Types", BCP 43, RFC 2939,
         September 2000.

   [RFC-2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
        Masinter, L., Leach, P.  and T.  Berners-Lee, "Hypertext
        Transfer Protocol -- HTTP/1.1" RFC 2616, June 1999.

   [RFC-959]  Postel, J. and J. Reynolds, "File Transfer Protocol
        (FTP)", STD 9, RFC 959, October 1985.

   [RFC-1436] F. Anklesaria, M. McCahill, P. Lindner, D. Johnson,
        D. Torrey and B. Albert, "The Internet Gopher Protocol
        (a distributed document search and retrieval protocol)",
        RFC 1436, March 1993.

   [RFC-977]  Kantor, B and P.  Lapsley, "Network News Transfer
        Protocol", RFC 977, February 1986.

   [RFC-1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
        L.  Jones, "SOCKS Protocol V5", RFC 1928, April 1996.


   [SSL2]  Hickman, Kipp, "The SSL Protocol", Netscape Communications
        Corp., Feb 9, 1995.

   [SSL3]     A.  Frier, P.  Karlton, and P.  Kocher, "The SSL 3.0
        Protocol", Netscape Communications Corp., Nov 18, 1996.

   [RFC-1625] M. St. Pierre, J. Fullton, K. Gamiel, J. Goldman, B. Kahle,
        J. Kunze, H. Morris, F. Schiettecatte, "WAIS over Z39.50-1988",
        RFC 1625, June 1994.

   [RDF-SYN]  Becket, D. and B. McBride, Ed., "RDF/XML Syntax Specification",
        W3C REC-rdf-syntax, February 2004,
        <http://www.w3.org/TR/rdf-syntax-grammar/>.



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Author's Address

   Senthil K Balasubramanian
   Intoto Software (I) Pvt Ltd
   Old No 3, New No 5, First Street,
   Nandanam Extension,
   Chennai, India 600 035

   Phone: +91 44 2827 5191
   EMail: ksenthil@intoto.com

   Michael Alexander
   Wirtschaftsuniversitaet Wien
   Augasse 2-6
   A-1090 Vienna, Austria

   Phone: +43 31336 4467
   Email: malexand@wu-wien.ac.at


   Gustaf Neumann
   Wirtschaftsuniversitaet Wien
   Augasse 2-6
   A-1090 Vienna, Austria

   Phone: +43 31336 4671
   Email: neumann@wu-wien.ac.at





























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