Internet Engineering Task Force SIP WG
Internet Draft H.Schulzrinne/B.Volz
Columbia University/Ericsson
draft-ietf-sip-dhcpv6-00.txt
April 7, 2002
Expires: October 2002
DHCPv6 Options for SIP Servers
STATUS OF THIS MEMO
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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Abstract
This document defines a DHCPv6 option that contains a list of domain
names or IPv6 addresses that can be mapped to one or more 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
This document uses the DHCP terminology defined in [1].
A SIP server is defined in RFC 3261 [2]. This server MUST be an
outbound proxy server, as defined in [3]. In the context of this
document, a SIP server refers to the host the SIP server is running
on.
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A SIP client is defined in RFC 3261 [2]. The client can be a user
agent client or the client portion of a proxy server. In the context
of this document, a SIP client refers to the host the SIP client is
running on.
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [4].
2 Introduction
The Session Initiation Protocol (SIP) [2] is an application-layer
control protocol that can establish, modify and terminate multimedia
sessions or calls. A SIP system has a number of logical components:
user agents, proxy servers, redirect servers and registrars. User
agents MAY contain SIP clients, proxy servers always do.
This draft specifies two DHCPv6 options [1] that allows SIP clients
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
the address identified in the SIP URL directly, without involving a
local SIP server. However in some circumstances, when firewalls are
present, SIP clients need to use a local server for outbound
requests.) This is one of many possible solutions for locating the
outbound SIP server; manual configuration is an example of another.
3 SIP Server DHCPv6 Option
This document defines two DHCPv6 options that describe a local
outbound SIP proxy: one carries a list of domain name (Section 3.1,
the other a list of 128-bit (binary) IPv6 addresses (Section 3.2).
Since DHCPv6 does not suffer from a shortage of option
codes, we avoid the encoding byte found in the IPv4 DHCP
option for SIP servers [5]. This makes the option shorter,
easier to parse, simplifies appropriate word alignment for
the numeric addresses and allows the client to request
either numeric or domain name options using the "option
request option".
An implementation implementing this specification MUST support both
options.
3.1 SIP Servers Domain Name List
The option length is followed by a sequence of labels, encoded
according to Section 3.1 of RFC 1035 [6], quoted below:
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"Domain names in messages are expressed in terms of a
sequence of labels. Each label is represented as a one
octet length field followed by that number of octets. Since
every domain name ends with the null label of the root, a
domain name is terminated by a length byte of zero. The
high order two bits of every length octet must be zero, and
the remaining six bits of the length field limit the label
to 63 octets or less. To simplify implementations, the
total length of a domain name (i.e., label octets and label
length octets) is restricted to 255 octets or less."
RFC 1035 encoding was chosen to accomodate future
internationalized domain name mechanisms.
The option MAY contain multiple domain names, but these SHOULD refer
to different NAPTR records, rather than different A records. The
client MUST try the records in the order listed, applying the
mechanism described in Section 4.1 of RFC XXXX [7] for each. The
client only resolves the subsequent domain names if attempts to
contact the first one failed or yielded no common transport protocols
between client and server or denote a domain administratively
prohibited by client policy. Domain names MUST be listed in order of
preference.
Use of multiple domain names is not meant to replace NAPTR
or SRV records, but rather to allow a single DHCP server to
indicate outbound proxy servers operated by multiple
providers.
Clients MUST support compression according to the encoding in Section
4.1.4 of "Domain Names - Implementation And Specification" [6].
The DHCPv6 option has the following format:
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_SIP_SERVER_D | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SIP Server Domain List |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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option-code: OPTION_SIP_SERVER_D (TBD)
option-length: Length of the 'SIP Server Domain Name List' field
in octets; variable
SIP Server Domain List: The domain names of the SIP outbound
proxy servers for the client to use. The domain names are
encoded as specified in section "Representation and use of
domain names" of the DHCPv6 specification [1].
3.2 SIP Servers IPv6 Address List
This option specifies a list of IPv6 addresses indicating SIP
outbound proxy servers available to the client. Servers MUST be
listed in order of preference.
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_SIP_SERVER_A | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SIP server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SIP server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_SIP_SERVER_A (TBD)
option-length: Length of the 'options' field in octets; must be
a multiple of 16.
SIP server: IPv6 address of a SIP server for the client to use.
The servers are listed in the order of preference for use
by the client.
4 Client Operation
A client may request either or both of the SIP Servers Domain Name
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List and SIP Servers IPv6 Address List options in an Options Request
Option (ORO) as described in [1],
If a client receives both the SIP Servers Domain Name List and SIP
Servers IPv6 Address List options, it SHOULD use the SIP Servers
Domain Name List option and ignore the SIP Servers IPv6 Address List
option.
5 Server Operation
A server MAY be configured to provide the SIP Servers Domain Name
List and SIP Servers IPv6 Address List options. A server MAY send a
client one or both of the SIP Servers Domain Name List and SIP
Servers IPv6 Address List options.
A server MAY send a client only one of these options, even if both
are requested by the client or configured in the server, but in this
case it SHOULD send the SIP Servers Domain Name List.
However, a server configured with the SIP Servers IPv6 Address List
option MUST send a client the SIP Servers IPv6 Address List option if
that client requested the SIP Servers IPv6 Address List option and
not the SIP Servers Domain Name List option in an ORO (see [1]).
The following table summarizes the server's response:
Client sends in ORO Domain Name List IPv6 Address List
__________________________________________________________________
Neither option SHOULD MAY
SIP Servers Domain Name List SHOULD MAY
SIP Servers IPv6 Address List MAY SHOULD
Both options SHOULD MAY
6 Security Consideration
The security considerations in RFC XXXX [1], RFC 3261 [2] and RFC
3263 [3] apply. If an adversary manages to modify the response from a
DHCP server or insert its own response, a SIP user agent could be led
to contact a rogue SIP server, possibly one that then intercepts call
requests or denies service. A modified DHCP answer could also omit
host names that translated to TLS-based SIP servers, thus
facilitating intercept.
7 IANA Considerations
IANA has assigned a DHCPv6 option number of TBD for the "SIP Servers
Domain Name List" and the DHCPv6 option number of TBD for the "SIP
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Servers IPv6 Address List" defined in this document.
8 Acknowledgements
TBD.
9 Authors' Addresses
Henning Schulzrinne
Dept. of Computer Science
Columbia University
1214 Amsterdam Avenue, MC 0401
New York, NY 10027
USA
electronic mail: schulzrinne@cs.columbia.edu
Bernie Volz
Ericsson
959 Concord Street
Framingham, MA 01701
USA
electronic mail: Bernie.Volz@am1.ericsson.se
10 Bibliography
[1] J. Bound, M. Carney, C. Perkins, T. Lemon, B. Volz, and R. Droms,
"Dynamic host configuration protocol for IPv6 (DHCPv6)," Internet
Draft, Internet Engineering Task Force, Feb. 2002. Work in progress.
[2] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
Peterson, R. Sparks, M. Handley, and E. Schooler, "Sip: Session
initiation protocol," Request for Comments 3261, Internet Engineering
Task Force, Mar. 2002.
[3] J. Rosenberg and H. Schulzrinne, "Sip: Locating sip servers,"
Request for Comments 3263, Internet Engineering Task Force, Mar.
2002.
[4] S. Bradner, "Key words for use in RFCs to indicate requirement
levels," Request for Comments 2119, Internet Engineering Task Force,
Mar. 1997.
[5] H. Schulzrinne, "DHCP option for SIP servers," Internet Draft,
Internet Engineering Task Force, Mar. 2002. Work in progress.
[6] P. V. Mockapetris, "Domain names - implementation and
specification," Request for Comments 1035, Internet Engineering Task
Force, Nov. 1987.
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[7] H. Schulzrinne and J. Rosenberg, "SIP: Locating SIP servers,"
Internet Draft, Internet Engineering Task Force, Feb. 2002. Work in
progress.
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