draft-ietf-sip-dhcp-06.txt   rfc3361.txt 
Internet Engineering Task Force SIP WG Network Working Group H. Schulzrinne
Internet Draft H.Schulzrinne Request for Comments: 3361 Columbia University
Columbia University Category: Standards Track August 2002
draft-ietf-sip-dhcp-06.txt
March 1, 2002
Expires: August 2002
DHCPv4 Option for SIP Servers
STATUS OF THIS MEMO
This document is an Internet-Draft and is in full conformance with Dynamic Host Configuration Protocol (DHCP-for-IPv4)
all provisions of Section 10 of RFC2026. Option for Session Initiation Protocol (SIP) Servers
Internet-Drafts are working documents of the Internet Engineering Status of this Memo
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material or to cite them other than as "work in progress". Official Protocol Standards" (STD 1) for the standardization state
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Abstract Abstract
This document defines a DHCP-for-IPv4 option that contains a list of This document defines a Dynamic Host Configuration Protocol
domain names or IPv4 addresses that can be mapped to one or more SIP (DHCP-for-IPv4) option that contains a list of domain names or IPv4
outbound proxy servers. This is one of the many methods that a SIP addresses that can be mapped to one or more Session Initiation
client can use to obtain the addresses of such a local SIP server. Protocol (SIP) outbound proxy servers. This is one of the many
methods that a SIP client can use to obtain the addresses of such a
local SIP server.
1 Terminology 1. Terminology
DHCP client: A DHCP [1] client is an Internet host that uses DHCP client: A DHCP [1] client is an Internet host that uses
DHCP to obtain configuration parameters such as a network DHCP to obtain configuration parameters such as a network
address. address.
DHCP server: A DHCP server is an Internet host that returns DHCP server: A DHCP server is an Internet host that returns
configuration parameters to DHCP clients. configuration parameters to DHCP clients.
SIP server: As defined in RFC 2543 [2]. This server MUST be an SIP server: As defined in RFC 3261 [2]. This server MUST be an
outbound proxy server, as defined in [3]. In the context of outbound proxy server, as defined in [3]. In the context of
this document, a SIP server refers to the host the SIP this document, a SIP server refers to the host the SIP
server is running on. server is running on.
SIP client: As defined in RFC 2543. The client can be a user SIP client: As defined in RFC 3261. The client can be a user
agent client or the client portion of a proxy server. In agent client or the client portion of a proxy server. In
the context of this document, a SIP client refers to the the context of this document, a SIP client refers to the
host the SIP client is running on. host the SIP client is running on.
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [4]. and "OPTIONAL" are to be interpreted as described in RFC 2119 [4].
2 Introduction 2. Introduction
The Session Initiation Protocol (SIP) [2] is an application-layer The Session Initiation Protocol (SIP) [2] is an application-layer
control protocol that can establish, modify and terminate multimedia control protocol that can establish, modify and terminate multimedia
sessions or calls. A SIP system has a number of logical components: sessions or calls. A SIP system has a number of logical components:
user agents, proxy servers, redirect servers and registrars. User user agents, proxy servers, redirect servers and registrars. User
agents MAY contain SIP clients, proxy servers always do. agents MAY contain SIP clients, proxy servers always do.
This draft specifies a DHCP option [1,5] that allows SIP clients to This document specifies a DHCP option [1,5] that allows SIP clients
locate a local SIP server that is to be used for all outbound SIP to locate a local SIP server that is to be used for all outbound SIP
requests, a so-called outbound proxy server. (SIP clients MAY contact requests, a so-called outbound proxy server. (SIP clients MAY
the address identified in the SIP URL directly, without involving a contact the address identified in the SIP URL directly, without
local SIP server. However in some circumstances, for example, when involving a local SIP server. However in some circumstances, for
firewalls are present, SIP clients need to use a local server for example, when firewalls are present, SIP clients need to use a local
outbound requests.) This is one of many possible solutions for server for outbound requests.) This is one of many possible
locating the outbound SIP server; manual configuration is an example solutions for locating the outbound SIP server; manual configuration
of another. is an example of another.
3 SIP Server DHCP Option 3. SIP Server DHCP Option
The SIP server DHCP option carries either a 32-bit (binary) IPv4 The SIP server DHCP option carries either a 32-bit (binary) IPv4
address or, preferably, a DNS (RFC 1035 [6]) fully-qualified domain address or, preferably, a DNS (RFC 1035 [6]) fully-qualified domain
name to be used by the SIP client to locate a SIP server. name to be used by the SIP client to locate a SIP server.
The option has two encodings, specified by the encoding byte ('enc') The option has two encodings, specified by the encoding byte ('enc')
that follows the code byte. If the encoding byte has the value 0, it that follows the code byte. If the encoding byte has the value 0, it
is followed by a list of domain names, as described below (Section is followed by a list of domain names, as described below (Section
3.1). If the encoding byte has the value 1, it is followed by one or 3.1). If the encoding byte has the value 1, it is followed by one or
more IPv4 addresses (Section 3.2). All implementations MUST support more IPv4 addresses (Section 3.2). All implementations MUST support
both encodings. The 'Len' field indicates the total number of octets both encodings. The 'Len' field indicates the total number of octets
in the option following the 'Len' field, including the encoding byte. in the option following the 'Len' field, including the encoding byte.
A DHCP server MUST NOT mix the two encodings in the same DHC message, A DHCP server MUST NOT mix the two encodings in the same DHCP
even if it sends two different instances of the same option. Attempts message, even if it sends two different instances of the same option.
to do so would result in incorrect client behavior as DHC processing Attempts to do so would result in incorrect client behavior as DHCP
rules call for the concatenation of multiple instances of an option processing rules call for the concatenation of multiple instances of
into a single option prior to processing the option [7]. an option into a single option prior to processing the option [7].
The code for this option is TBD. The code for this option is 120.
3.1 Domain Name List 3.1 Domain Name List
If the 'enc' byte has a value of 0, the encoding byte is followed by If the 'enc' byte has a value of 0, the encoding byte is followed by
a sequence of labels, encoded according to Section 3.1 of RFC 1035 a sequence of labels, encoded according to Section 3.1 of RFC 1035
[6], quoted below: [6], quoted below:
Domain names in messages are expressed in terms of a Domain names in messages are expressed in terms of a sequence
sequence of labels. Each label is represented as a one of labels. Each label is represented as a one octet length
octet length field followed by that number of octets. Since field followed by that number of octets. Since every domain
every domain name ends with the null label of the root, a name ends with the null label of the root, a domain name is
domain name is terminated by a length byte of zero. The terminated by a length byte of zero. The high order two bits
high order two bits of every length octet must be zero, and of every length octet must be zero, and the remaining six bits
the remaining six bits of the length field limit the label of the length field limit the label to 63 octets or less. To
to 63 octets or less. To simplify implementations, the simplify implementations, the total length of a domain name
total length of a domain name (i.e., label octets and label (i.e., label octets and label length octets) is restricted to
length octets) is restricted to 255 octets or less. 255 octets or less.
RFC 1035 encoding was chosen to accomodate future RFC 1035 encoding was chosen to accommodate future internationalized
internationalized domain name mechanisms. domain name mechanisms.
The minimum length for this encoding is 3. The minimum length for this encoding is 3.
The option MAY contain multiple domain names, but these SHOULD refer The option MAY contain multiple domain names, but these SHOULD refer
to different NAPTR records, rather than different A records. The to different NAPTR records, rather than different A records. The
client MUST try the records in the order listed, applying the client MUST try the records in the order listed, applying the
mechanism described in Section 4.1 of RFC XXXX [3] for each. The mechanism described in Section 4.1 of RFC 3263 [3] for each. The
client only resolves the subsequent domain names if attempts to client only resolves the subsequent domain names if attempts to
contact the first one failed or yielded no common transport protocols contact the first one failed or yielded no common transport protocols
between client and server or denote a domain administratively between client and server or denote a domain administratively
prohibited by client policy. prohibited by client policy.
Use of multiple domain names is not meant to replace NAPTR Use of multiple domain names is not meant to replace NAPTR and
and SRV records, but rather to allow a single DHCP server SRV records, but rather to allow a single DHCP server to
to indicate outbound proxy servers operated by multiple indicate outbound proxy servers operated by multiple providers.
providers.
Clients MUST support compression according to the encoding in Section Clients MUST support compression according to the encoding in Section
4.1.4 of "Domain Names - Implementation And Specification" [6]. 4.1.4 of "Domain Names - Implementation And Specification" [6].
Since the domain names are supposed to be different Since the domain names are supposed to be different domains,
domains, compression will likely have little effect, compression will likely have little effect, however.
however.
If the length of the domain list exceeds the maximum permissible If the length of the domain list exceeds the maximum permissible
within a single option (254 octets), then the domain list must be within a single option (254 octets), then the domain list MUST be
represented in the DHCP message as specified in [7]. represented in the DHCP message as specified in [7].
The DHCP option for this encoding has the following format: The DHCP option for this encoding has the following format:
Code Len enc DNS name of SIP server Code Len enc DNS name of SIP server
+-----+-----+-----+-----+-----+-----+-----+-----+-- +-----+-----+-----+-----+-----+-----+-----+-----+--
| TBD | n | 0 | s1 | s2 | s3 | s4 | s5 | ... | 120 | n | 0 | s1 | s2 | s3 | s4 | s5 | ...
+-----+-----+-----+-----+-----+-----+-----+-----+-- +-----+-----+-----+-----+-----+-----+-----+-----+--
As an example, consider the case where the server wants to offer two As an example, consider the case where the server wants to offer two
outbound proxy servers, "example.com" and "example.net". These would outbound proxy servers, "example.com" and "example.net". These would
be encoded as follows: be encoded as follows:
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|TBD|27 | 0 | 7 |'e'|'x'|'a'|'m'|'p'|'l'|'e'| 3 |'c'|'o'|'m'| 0 | |120|27 | 0 | 7 |'e'|'x'|'a'|'m'|'p'|'l'|'e'| 3 |'c'|'o'|'m'| 0 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+ | 7
| 7 |'e'|'x'|'a'|'m'|'p'|'l'|'e'| 3 |'n'|'e'|'t'| 0 | |'e'|'x'|'a'|'m'|'p'|'l'|'e'| 3 |'n'|'e'|'t'| 0 | +---+---+---
+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+
3.2 IPv4 Address List 3.2 IPv4 Address List
If the 'enc' byte has a value of 1, the encoding byte is followed by If the 'enc' byte has a value of 1, the encoding byte is followed by
a list of IPv4 addresses indicating SIP outbound proxy servers a list of IPv4 addresses indicating SIP outbound proxy servers
available to the client. Servers MUST be listed in order of available to the client. Servers MUST be listed in order of
preference. preference.
Its minimum length is 5, and the length MUST be a multiple of 4 plus Its minimum length is 5, and the length MUST be a multiple of 4 plus
one. The DHCP option for this encoding has the following format: one. The DHCP option for this encoding has the following format:
Code Len enc Address 1 Address 2 Code Len enc Address 1 Address 2
+-----+-----+-----+-----+-----+-----+-----+-----+-- +-----+-----+-----+-----+-----+-----+-----+-----+--
| TBD | n | 1 | a1 | a2 | a3 | a4 | a1 | ... | 120 | n | 1 | a1 | a2 | a3 | a4 | a1 | ...
+-----+-----+-----+-----+-----+-----+-----+-----+-- +-----+-----+-----+-----+-----+-----+-----+-----+--
4 Security Consideration 4. Security Considerations
The ecurity considerations in RFC 2131 [1], RFC 2543 [2] and RFC XXXX The security considerations in RFC 2131 [1], RFC 2543 [2] and RFC
[3] apply. If an adversary manages to modify the response from a DHCP 3263 [3] apply. If an adversary manages to modify the response from
server or insert its own response, a SIP user agent could be led to a DHCP server or insert its own response, a SIP user agent could be
contact a rogue SIP server, possibly one that then intercepts call led to contact a rogue SIP server, possibly one that then intercepts
requests or denies service. A modified DHCP answer could also omit call requests or denies service. A modified DHCP answer could also
host names that translated to TLS-based SIP servers, thus omit host names that translated to TLS-based SIP servers, thus
facilitating intercept. facilitating intercept.
5 IANA Considerations 5. IANA Considerations
IANA has assigned a DHCP option number of TBD for the "SIP Servers IANA has assigned a DHCP option number of 120 for the "SIP Servers
DHCP Option" defined in this document. DHCP Option" defined in this document.
6 Acknowledgements 6. Acknowledgements
Ralph Droms, Robert Elz, Wenyu Jiang, Peter Koch, Gautam Nair, Thomas Ralph Droms, Robert Elz, Wenyu Jiang, Peter Koch, Gautam Nair, Thomas
Narten, Erik Nordmark, Jonathan Rosenberg, Kundan Singh, Sven Ubik, Narten, Erik Nordmark, Jonathan Rosenberg, Kundan Singh, Sven Ubik,
Bernie Volz and Dean Willis provided useful feedback through the Bernie Volz and Dean Willis provided useful feedback through the
evolution of this draft. evolution of this document.
7 Authors' Addresses 7. Bibliography
[1] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March
1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[3] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[4] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", BCP 14, RFC 2119, March 1997.
[5] Alexander, S. and R. Droms, "DHCP options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[6] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[7] Lemon, T. and S. Cheshire, "Encoding Long DHCP Options", Work in
Progress.
8. Author's Address
Henning Schulzrinne Henning Schulzrinne
Dept. of Computer Science Dept. of Computer Science
Columbia University 1214 Amsterdam Avenue, MC 0401 Columbia University
1214 Amsterdam Avenue, MC 0401
New York, NY 10027 New York, NY 10027
USA USA
electronic mail: schulzrinne@cs.columbia.edu
8 Bibliography EMail: schulzrinne@cs.columbia.edu
[1] R. Droms, "Dynamic host configuration protocol," Request for 9. Full Copyright Statement
Comments 2131, Internet Engineering Task Force, Mar. 1997.
[2] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: Copyright (C) The Internet Society (2002). All Rights Reserved.
session initiation protocol," Request for Comments 2543, Internet
Engineering Task Force, Mar. 1999.
[3] H. Schulzrinne and J. Rosenberg, "SIP: Session initiation This document and translations of it may be copied and furnished to
protocol -- locating SIP servers," Internet Draft, Internet others, and derivative works that comment on or otherwise explain it
Engineering Task Force, Mar. 2001. Work in progress. or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
[4] S. Bradner, "Key words for use in RFCs to indicate requirement The limited permissions granted above are perpetual and will not be
levels," Request for Comments 2119, Internet Engineering Task Force, revoked by the Internet Society or its successors or assigns.
Mar. 1997.
[5] S. Alexander and R. Droms, "DHCP options and BOOTP vendor This document and the information contained herein is provided on an
extensions," Request for Comments 2132, Internet Engineering Task "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
Force, Mar. 1997. TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
[6] P. V. Mockapetris, "Domain names - implementation and Acknowledgement
specification," Request for Comments 1035, Internet Engineering Task
Force, Nov. 1987.
[7] T. Lemon and S. Cheshire, "Encoding long DHCP options," Internet Funding for the RFC Editor function is currently provided by the
Draft, Internet Engineering Task Force, Oct. 2001. Work in progress. Internet Society.
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