DCCP WG G.Fairhurst
Internet Draft University of Aberdeen
Expires: September 2007 June 19, 2007
The DCCP Service Code
draft-ietf-dccp-serv-codes-00.txt
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Abstract
This document describes the usage of Service Codes by the Datagram
Congestion Control Protocol, RFC 4340. Service Codes provide a method
to identify the intended service/application to process a DCCP
connection request. This provides improved flexibility in the use and
assignment of port numbers for connection multiplexing. The use of a
DCCP Service Code can also enable more explicit coordination of
services behind network address translators and firewalls. This
document motivates the setting of Service Codes by applications,
rather than assigning a default Service Code value of zero. This
updates the description provided in RFC4 4340.
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Table of Contents
1. Introduction...................................................3
1.1. Conventions used in this document.........................4
2. An Architecture for supporting Service Codes...................5
2.1. IANA Port Numbers.........................................5
2.2. DCCP Service Code Values..................................6
2.3. Zero Service Code.........................................6
2.4. Reception of a DCCP-Request with a bound Service Code.....8
2.5. Reception of a DCCP-Request with an unbound Service Code
....................................Error! Bookmark not defined.
2.6. SDP for describing Service Codes..........................6
2.7. Service Code Registry.....................................7
3. Use of the DCCP Service Code...................................7
3.1. Setting Service Codes at the Sender.......................7
3.2. Using Service Codes in the Network........................7
3.3. Using Service Codes at the Receiver.......................8
3.4. Multiple Associations of Service Codes and Ports at Sender9
3.5. Summary of Service Code and Port Handling.................9
4. Implementation Support for Service Codes......................10
4.1. Minimal Support..........................................10
4.2. Standard Support.........................................10
4.3. Enhanced Support.........................................11
4.4. Tests to indicate the level of Support...................11
5. Changes required to the API to support Service Codes..........12
5.1. Interactions with IPsec..................................15
6. Service Code Registry.........................................12
7. Benchmarking Services Described in this document..............13
7.1. Echo.....................................................13
7.2. Daytime..................................................13
7.3. Character generator......................................13
7.4. Time service.............................................14
7.5. PerfTest service.........................................14
8. Security Considerations.......................................14
8.1. Interactions of Service Codes and port numbers...........15
9. IANA Considerations...........................................16
9.1. Port number values allocated by this document............16
9.2. Service Code values allocated by this document...........17
10. Conclusions..................................................17
11. Acknowledgments..............................................18
12. References...................................................19
12.1. Normative References....................................19
12.2. Informative References..................................19
13. Author's Addresses...........................................21
13.1. Intellectual Property Statement.........................21
13.2. Disclaimer of Validity..................................21
13.3. Copyright Statement.....................................22
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APPENDIX A: Informative Examples of Host Configuration...........23
1. Introduction
Most Internet transport protocols use "well-known" port numbers
[RFC814] to indicate which application service is associated with a
connection or message; this includes TCP [RFC793], UDP [RFC768], SCTP
[RFC2960], UDP-Lite [RFC3828], and DCCP [RFC4340]. Making a port
number well-known involves registration with the Internet Assigned
Numbers Authority (IANA), which includes defining a service by a
unique keyword and reserving a port number from among a fixed pool
[IANA].
DCCP specifies a Service Code as a 4-byte value (32 bits). This
describes the application-level service to which a client application
wishes to connect ([RFC4340], Section 8.1.2). A Service Code
identifies the protocol (or a standard profile, e.g. [ID.DCCP.RTP])
to be used at the application layer. It is not intended to be used to
specify a variant of an application, or a specific variant of a
protocol.
Service Codes allow a flexible correspondence between application-
layer services and port numbers, which affects how applications
interact with DCCP. This decouples the use of ports for connection
demultiplexing and state management from their use to indicate a
desired service. Only one application may listen on a specific port
at any time, however when accepting a new connection, a port may be
associated with more than one Service Code (the requested Service
Code may then select the application).
The use of Service Codes can assist in identifying the intended
service when the server is located behind a network address
translator (NAT) [RFC2663], [RFC2766] that modifies the port numbers
associated with a flow. Middle-boxes (e.g. NATs, Firewalls) that
desire to identify the type of data being transported by a flow,
SHOULD utilize the Service Code for this purpose. When consistently
used, the Service Code can provide a more specific indication of the
actual service (e.g. indicating the type of multimedia flow, or
intended application behaviour).
Use of a Service Code value, instead of binding a service to a
particular publicly-known port number, permits a larger number of
concurrent connections for a particular service. For example, this
may be useful for applications where servers need to handle very
large numbers of simultaneous open ports to the same service.
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If an application does not set a Service Code, the connection is
associated with a Service Code of zero, with the intended server
identified only by the destination port number.
1.1. Conventions used in this document
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 [RFC2119].
All protocol code points and values are transmitted in network byte
order (most significant byte first), with the most significant bit of
each byte is placed in the left-most position of an 8-bit field.
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2. An Architecture for supporting Service Codes
DCCP defines the use of a combination of ports and Service Codes to
identify the server application ([RFC4340], 8.1.2). These are
described in the following sections. Section 3 describes the use of
Service Codes by hosts and network middleboxes.
2.1. IANA Port Numbers
In DCCP, an endpoint address is associated with a port number,
forming a socket; and a pair of sockets uniquely identifies each
connection. Ports provide the fundamental de-multiplexing function.
Like DCCP, most Internet transport protocols (e.g. TCP [RFC793], UDP
[RFC768]) also define publicly-known ports for most services, whether
intended for public access (e.g., telnet, DNS) or for services
typically used between pre-arranged pairs (e.g., X11, SSH). In TCP
and UDP these are the primary means of identifying the required
service when a connection request is received.
The Internet Assigned Numbers Authority currently manages the set of
globally reserved port numbers [IANA]. The destination port value
that is associated with a service is determined either by an
operating system index to a copy of the IANA table (e.g.,
getportbyname() in Unix, which indexes the /etc/services file), or
directly mapped by the application.
The UDP and TCP port number space: 0..65535, is split into three
ranges [RFC2780]:
o 0..1023 "well-known", also called "system" ports
o 1024..49151 "registered", also called "user" ports
o 49152..65535 "dynamic", also called "private" ports
One challenge with the use of IANA-managed ports is that this
allocates ports globally, for all hosts on the public Internet, even
though the association between a port and a service is of interest
only to the hosts participating in a connection. As a result, the
fixed space of port numbers is being globally reserved unnecessarily.
It is more useful to allocate this name space on a per-host basis
[ID.Portnames].
Well-known/Reserved DCCP ports are described in a separate IANA
registry [RFC4340]. This registry may also associate ports with a
pre-defined set of Service Codes (see section 2.2).
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The source port associated with a connection request, often known as
the "ephemeral port", traditionally includes the range 49152-65535,
and should also include the 1024-49151 range. The value used for the
ephemeral port is usually chosen by the client operating system. It
has been suggested that a randomized choice of port number value can
help defend against "blind" attacks [ID.TSVWG.RAND] in TCP. Such
methods may be applicable to other IETF-defined transport protocols,
including DCCP.
2.2. DCCP Service Code Values
DCCP specifies a 4 byte Service Code [RFC4340]. Service codes may be
represented in one of three forms as: a decimal number (the canonical
method), a four character ASCII string, or an eight digit hexadecimal
number.
The Service Code identifies the application-level service to which a
client application wishes to connect. Examples of services are RTP,
TIME, ECHO. In a different example, DTLS provides a transport-service
(not an application-layer service), therefore applications using DTLS
are individually identified by a set of corresponding service codes.
The Service Code is present only in DCCP-Request and DCCP-Response
packets and permits a more flexible correspondence between services
and port numbers than is possible using the corresponding socket pair
(4-tuple of layer-3 addresses and layer-4 ports). This decouples the
use of ports for connection demultiplexing and state management, from
their use to indicate a desired endpoint service.
Service Codes allow a larger number of concurrent connections for a
particular service than possible using well-known port numbers, by
allowing endpoints to use a set of port numbers for the services they
deploy (c.f. section 2.1).
2.3. Zero Service Code
A Service Code value of zero indicates that the Service Code function
is not used by a client. A server uses only the destination port
number to identify the required application-service (section 2.1).
2.4. SDP for describing Service Codes
Methods that currently signal the use of port numbers, such as the
Session Description Protocol (SDP) require extension to support DCCP
Service Codes [ID.DCCP.RTP].
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2.5. Service Code Registry
The set of Service Codes currently specified for use within the
general Internet are defined in an IANA-controlled name space. IANA
manages new allocations of Service Codes in this space [RFC4340].
Associations of Service Code with Ports may also be defined in the
IANA DCCP Port Registry.
3. Use of the DCCP Service Code
Like UDP, DCCP uses port numbers to demultiplex connections. Upon
receipt of a DCCP-Request the Service Code value is matched against a
list of available services.
3.1. Setting Service Codes at the Sender
A client application SHOULD associate a DCCP-Request packet with a
Service Code value that identifies the intended application-service
to be used. Valid Service Codes are selected from the set of values
assigned in the DCCP Service Code Registry maintained by IANA [IANA-
SC], or from the uncoordinated private space ([RFC4340], 8.1.2.). An
application that does not set a Service Code, MUST be associated with
a Service Code value of zero.
3.2. Using Service Codes in the Network
Port numbers and IP addresses are the accepted methods to identify a
flow within an IP network. When the DCCP header has not been
encrypted, Middleboxes [RFC3234], such as firewalls, can instead use
the Service Code to identify the application-service (even when
running on a non-standard port). Middlebox devices are therefore
expected to check Service Code values before port numbers for DCCP.
The Service Code values in DCCP-Requests should be used for
supplementary checks [RFC4340]. Section 4.1 describes some issues
that may arise in this case.
The use of the DCCP Service Code can potentially lead to interactions
with other protocols that interpret or modify DCCP port numbers. This
includes IPsec and other firewall systems, other security mechanisms,
other in-band exchange of port numbers, and NATs [RFC2663],
[RFC2776]. Network address and port translators, known collectively
as NATs, not only interpret DCCP ports, but may also translate/modify
them [RFC2993]. This interferes with the use of ports for service
identification [RFC3234]. The DCCP Service Code may allow services to
be identified behind NATs, if NATs are not further extended to
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translate Service Codes. This document therefore recommends that
Middleboxes SHOULD NOT modify the Service Code, unless they also
change the service that a connection is accessing.
DCCP connections identified by the Service Code continue to use IP
addresses and ports, although neither port number may be well-
known/reserved. Translation of these ports need to be considered in
the operation of NATs. In addition, DCCP Service Codes can reduce the
need to correctly interpret port numbers, leading to new
opportunities for network address and port translators.
3.3. Using Service Codes at the Receiver
A Service Code is used by the host that receives a DCCP-Request to
associate a DCCP connection with the corresponding application-
service. At the server, this association must be explicit, i.e. if
the connection is accepted, the requested Service Code MUST have been
previously associated with the destination port at the server.
An implementation MUST allow a server to be associated with a Service
Code on a fixed port. The Service Code of zero MAY be the default,
indicating that no specific Service Code is in use. An implementation
MAY also allow a server to set a Service Code that applies to a set
of acceptable destination port values.
3.3.1. Reception of a DCCP-Request
When a DCCP-Request is received, and the specified destination port
is not bound to a server, the host MUST reject the connection by
issuing a DCCP-Reset with Reset Code "Connection Refused". A host
MAY also use the Reset Code "Too Busy" ([RFC4340], 8.1.3).
When the destination port is bound to a server, the host MUST also
verify that the port has been associated with the specified Service
Code. A Service Code of zero MUST only be accepted for servers that
have no associated Service Code or are explicitly associated with the
Service Code value of zero. Two cases can occur:
o If the receiving host is listening on the specified destination
port number and the Service Code of the DCCP-Request matches one
of the Service Codes associated with this Port, the host accepts
the connection. Once connected, the server returns a copy of the
Service Code in the DCCP-Response packet completing the initial
handshake [RFC4340].
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o If the port is not associated with the requested Service Code,
then the host MUST reject the connection by issuing a DCCP-Reset
with the reset code "Bad Service Code"([RFC4340], 8.1.2).
3.3.2. Multiple Associations of Service Codes and Ports at the Server
A Service Code MAY be associated with more than one destination port
(wildcarding a set of port values). Also a single destination port
MAY be associated with multiple Service Codes (wildcarding a set of
Service Codes), although an active (open) connection can only be
associated with a single Service Code [RFC4340].
A host implementation may provide a method that only allows a single
Service Code to be associated with each listening port. This means
that a single port can only be used for a pre-specified service.
When the service associated with a port is not permanently running
at the Server, the arrival of a DCCP-Request may require launching
an application server to accept messages from the DCCP connection.
This operation could resemble that of "inetd". The server needs to
provide a method to ensure that the DCCP-Request is associated with
a server that handles the corresponding Service Code. This may allow
a server to offer more than the limit of 65,536 services determined
by the size of the Port field (fewer if system/user/dynamic
boundaries are preserved). The limit is based solely on the number
of unique connections between two hosts (i.e., 4,294,967,296).
As in the previous section, when the specified Service Code is not
associated with the specified port, the server MUST abort the
connection and send a DCCP Reset message.
3.4. Summary of Service Code and Port Handling
The basic operation of the Service Codes is as follows:
o A source host may:
. issue a DCCP-Request with a Service Code of zero and choose
either a well-known/reserved destination port or a port number
announced by some other means.
. issue a DCCP-Request with a non-zero Service Code and choose a
destination port number that is associated with the specified
Service Code at the destination.
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o A server may receive a DCCP-Request with a:
. zero Service Code. It validates that the port supports a
Service Code of zero and then uses the destination port to
identify the associated server.
. non-zero Service Code, It determines whether an available
service matching the Service Code is supported for the
specified destination port. The session is associated with a
corresponding server, and a DCCP-Response is returned.
o If the service is not available, the session is rejected and a
DCCP-Reset packet is returned.
4. Implementation Support for Service Codes
This document does not define how to implement Service Codes on a
particular platform or using a specific operating system. It does
define three levels of support that may be offered.
4.1. Minimal Support
All Servers MUST be capable of accepting a DCCP-Request that contains
a zero Service Code. These may be handled in the same way as other
transport connections (e.g. UDP, TCP). At this level, a DCCP-Request
with a non-zero Service Code MUST result in the connection being
rejected. This limits interoperability with other levels. This model
is suitable for platforms with limited capability, but is NOT
RECOMMENDED for general use.
4.2. Standard Support
At this level of support, a server accepts a DCCP-Request that
contains any value of Service Code, including zero. The Service Code
specified in a DCCP-Request message is checked against an internal
database to determine whether the Service Code is associated with the
port. This model is RECOMMENDED for general use.
The design could be simplified if a single default Service Code were
to be associated with a set of specific well-known ports, allowing a
port to be mapped via a library or operating system function to a
corresponding default Service Code (simplifying the association).
Such a system however also MUST provide a way to allow a sending
and/or receiving application to associate a non-default Service Code
(specified by the application). Some higher layer protocols (e.g. RTP
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[ID.DCCP.RTP]) are not associated with a single well-known port and
must therefore use this latter method.
4.3. Enhanced Support
A server offering Enhanced Support provides finer and more flexible
control of the use of Service Codes and port numbers. This permits a
receiver to accept DCCP-Requests with arbitrary mappings between
Service Codes and port ranges, associating each connection with the
appropriate application server (section 3.3.2). A single destination
port number may be associated with more than one Service Code value.
These may be associated with one or different server applications.
This level of support may require operating systems to use a modified
process to handle in-coming DCCP-Request packets and may allow
policies to be defined. Appendix A provides some examples of methods
that may be used to configure this support.
4.4. Tests to indicate the level of Support
This section defines a series of tests that may be used to identify
the level of support provided by a remote DCCP host.
o A client should always be able to contact a remote server using
DCCP with a Service Code of zero on the port associated with the
test service. A server offering Minimal Support will accept this
connection and return a single packet response. A server offering
Standard or Enhanced Support will reset the connection.
o A client testing for Standard Support could initiate a DCCP
connection to a server using the port associated with the test
service, and specifying a Service Code of TEST. A server offering
either Standard Support or Enhanced Support will accept this
connection and return a single packet response. A server offering
only Minimal Support will reset the connection.
o A client testing for Enhanced Support could initiate a DCCP
connection to a server using the port associated with the DISC
service, but which specifies a Service Code of TEST (identifying
the test service). A server offering Enhanced Support server that
allows the TEST service to run on this port will accept the
connection and return a single packet response. Other servers will
reset the connection.
The above tests require services to be supported by the server and
permitted by the network and host security policies (see section 8).
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>>> These tests could encourage open deployment of the test service,
which may result in a security vulnerability - - is this OK? <<<
5. Changes required to the API to support Service Codes
The use of Service Codes requires an API that allows a service to be
associated with a Service Code in addition to a port number. One
approach is to use separate commands as follows:
o Extend the existing port number indicator command (e.g., Unix
bind() or connect() calls) to also select a specific Service Code
where desired.
o Extend the existing socket parameterization command (e.g., Unix
setsockopt()) to set a service-code option. This is implemented in
the present Linux API for a DCCP socket (where the Service Code
should be wrapped by htonl/ntohl to ensure network byte order).
o An information base (table) may be used by servers to identify the
set of Service Codes that are associated with each port and the
corresponding set of server applications.
>>> Author note:
May need to discuss:
get_port_and_service_code_by_name(char *what_service_do_you_want)
char *get_service_code_by_number(unsigned sc)
and interactions with getadddrinfo() address/port lookup routine,
which has been introduced to simplify the migration to IPv6
([RFC3493], 6.1).
Functions such as getnameinfo and getservent may also need to be
updated.
>>> End Author Note.
6. Service Code Registry
The set of Service Codes currently specified for use within the
general Internet are defined in an IANA-controlled name space. IANA
manages new allocations of Service Codes in this space [RFC4340].
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Service Code bindings to Ports may also be defined in the IANA DCCP
Port Registry.
7. Benchmarking Services Described in this document
A number of simple services are commonly supported by systems using
DCCP and UDP, this section defines corresponding services for DCCP.
These services are useful to debug and benchmark bidirectional DCCP
connections. The IANA section of this document allocates a
corresponding set of code points for these services.
7.1. Echo
The operation of the DCCP echo service follows that specified for UDP
[RFC862]: a server listens for DCCP connections; once a client has
set up a connection, each data packet sent to the server will be
copied (echoed) back to the client.
7.2. Test
The operation of the DCCP test service is as follows: a server
listens for DCCP connections; once a client has set up a connection,
one data packet is returned to the client. The server then resets the
connection.
This service may be provided with a Service Code of zero, when a
server provides Basic Support, to facilitate testing. To facilitate
testing of a server provides Enhanced Support, this service may be
provided as an additional service on port 9.
7.3. Daytime
The DCCP daytime service is operationally equivalent to the
connection-based TCP daytime service [RFC867]: any data received is
discarded by the server; and generates a response sent in a DCCP data
packet containing the current time and data as an ASCII string; after
which the connection is closed.
7.4. Character generator
The operation of the DCCP chargen service corresponds to the
connection-based TCP chargen protocol [RFC864]: A server listens for
incoming requests and, once a client has established a connection,
continuously sends datagrams containing a random number (between 0
and 512, up to the current path MTU) of characters. The service
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terminates when the user either closes or aborts the connection.
Congestion control is enforced using the mechanisms [RFC4340] and
related documents.
If necessary the receiver can enforce flow control on this service by
using either or both of the Slow Receiver ([RFC4340], 11.6) and Data
Dropped ([RFC4340], 11.7) options to signal the server to slow down.
The chargen protocol provides a useful service that may be used for
testing and measurement of bidirectional DCCP connectivity, as well
as congestion control responsiveness. The datagram-based variant of
chargen can be emulated with the DCCP ECHO service by changing the
format of the datagrams sent by the client, hence these services
complement each other.
7.5. Time service
The format of timestamps and the operation of the DCCP time service
is equivalent with the TCP time protocol variant [RFC868]: a server
listens for incoming connections; after a client has established a
new connection, the server sends a 4-byte timestamp; whereupon the
client closes the connection.
7.6. PerfTest service
The PerfTest concept specified by this document provides a generic
service that may be used to benchmark and measure both unidirectional
and bidirectional DCCP connections, as well as server and host DCCP
stacks.
This document defines a generic PerfTest service. The payload of DCCP
packets associated with the DCCP PerfTest service are silently
discarded by the receiver, and used only for gathering numerical
performance data.
The PerfTest server is identified by a combination of the port number
and DCCP Service Code. It does not recommend a specific benchmarking
software to use, but does allocate a port number specified that
currently coincides with that of the open-source iperf benchmarking
program [iperf].
8. Security Considerations
This document does not describe new protocol functions.
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The document discusses the usage of Service Codes. There are three
areas of security that are important:
1. Interaction with NATs and firewalls (see section 3.2, on middlebox
behaviour).
2. Interpretation of DCCP Service Codes over-riding traditional use
of reserved/well-known port numbers (see section 8.1)
3. Interaction with IPsec and DTLS security (see section 8.2, on use
of IPsec).
4. Services used for benchmarking and testing may also be used to
generate traffic for other purposes, and pose an opportunity for a
Denial of Service attack. Care needs to be exercised when enabling
these services in an operational network, or appropriate rate-
limits should be provided to mitigate these effects.
8.1. Interactions of Service Codes and port numbers
The Service Code value may be used to over-ride the traditional way
that operating systems consider low-numbered ports as privileged.
This represents a change in the way operating systems respect this
range of DCCP port numbers.
The same service (application) may be potentially accessed using more
than one Service Code. Examples include the use of separate Service
Codes for an application layered directly upon DCCP and one using
DTLS transport over DCCP. Other possibilities include the use of a
private Service Code point that maps to the same application as
assigned to an IANA-defined Service Code value. Different versions of
a service (application) may also be mapped to a corresponding set of
Service Code values. Care needs to be exercised when interpreting the
mapping the Service Code value to the corresponding service.
Processing of Service Codes may imply more processing than currently
associated with incoming port numbers. Implementers need to guard
against increasing opportunities for Denial of Service attack.
8.2. Interactions with IPsec
IPsec uses port numbers to perform access control in transport mode
[RFC4301]. Security policies can define port-specific access control
(PROTECT, BYPASS, DISCARD), as well as port-specific algorithms and
keys. Similarly, firewall policies allow or block traffic based on
port numbers.
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Use of port numbers in IPsec selectors and firewalls may assume that
the numbers correspond to well-known services. It is useful to note
that there is no such requirement; any service may run on any port,
subject to mutual agreement between the endpoint hosts. Use of the
Service Code may interfere with this assumption both within IPsec and
in other firewall systems, but it does not add a new vulnerability.
New implementations of IPsec and firewall systems may interpret the
Service Code when implementing policy rules, but should not rely on
either port numbers or Service Codes to indicate a specific service.
This is not an issue for IPsec because the entire DCCP header and
payload are protected by all IPsec modes. None of the DCCP header is
protected by application-layer security, e.g., DTLS [ID.DTLS.DCCP],
so again this is not an issue [RFC4347].
9. IANA Considerations
A set of new services are defined in section 6 and are summarized in
this section.
9.1. Port number values allocated by this document
IANA action is required to assign ports for use by DCCP. This
document requests allocation of the following code points from the
IANA DCCP Port numbers registry:
>>>>>> IANA ACTION Please replace IANA THIS RFC, with the allocated
RFC number. <<<
>>>>>> IANA ACTION Please assign a port number for use by the test
method <<<
echo 7/dccp Echo SC:ECHO
# IETF dccp WG, [IANA - THIS RFC]
echo [IANA-Assign a value] /dccp test SC:TEST
# IETF dccp WG, [IANA - THIS RFC]
daytime 13/dccp DayTime SC:DTIM
# IETF dccp WG, [IANA - THIS RFC]
chatgen 19/dccp Chargen SC:CHAR
# IETF dccp WG, [IANA - THIS RFC]
time 37/dccp Timeserver SC:TIME
# IETF dccp WG, [IANA - THIS RFC]
perf 5001/dccp PerfTest SC:PERF
# IETF dccp WG, [IANA - THIS RFC]
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9.2. Service Code values allocated by this document
This document solicits IANA action to allocate the following code
points from the Service Code registry [IANA-SC]. The requested
assignments are listed below and summarized in table 1. This set of
Service Codes may be utilized for testing DCCP implementations and
transmission paths.
>>> IANA Please replace tbd by the assigned a port number in section
9.1.
+----------+------+----+-------------------------------+----------+
| Service | ASCII|Port| Description | Ref |
| Code (SC)| Code | | | |
+----------+------+----+-------------------------------+----------+
|0x4543484f| ECHO | 7| Echo service | [RFC862] |
|0x54455354| TEST | tbd| Test Service | [THISRFC]|
|0x4454494d| DTIM | 13| Daytime server | [RFC867] |
|0x43484152| CHAR | 19| Character generator (chargen) | [RFC864] |
|0x54494d45| TIME | 37| Timeserver | [RFC868] |
|0x50455246| PERF |5001| Performance tests (e.g. | * |
| | | | iperf, ttcp, ...) | |
+----------+------+----+-------------------------------+----------+
Table 1: Allocation of Service Codes by this document.
Notes:
1) Port is the default port associated with this service.
2) * Reference is this document.
>> Author note, the I-D should finally use decimal allocations of the
Service Code Valus.
The document notes that it is NOT required to supply an approved
document (e.g. a published RFC) to support an application for a DCCP
Service Code or port number value, although RFCs may be used to
request Service Code values via the IANA Considerations section (e.g.
[ID.DTLS.DCCP], [ID.DCCP.RTP]).
10. Conclusions
This document discusses the operation of service codes by the DCCP
transport protocol [RFC4340] and motivates their use. The document
augments and clarifies the way in which DCCP applications should use
the Service Code Feature. It does updates, but does not obsolete, the
protocol defined in RFC4340.
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Service Codes, or similar concepts may also be useful to other IETF
transport protocols [ID.Portnames]).
11. Acknowledgments
This work has been supported by the EC IST SatSix Project.
Significant contributions to this document resulted from discussion
with Joe Touch, and this is gratefully acknowledged. The author also
thanks Ian McDonald, Fernando Gont, and the DCCP WG for helpful
comments on this topic, and Gerrit Renker for his help in determining
DCCP behaviour, review of the document, and compilation of useful
test applications defined in the IANA section of this document.
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12. References
12.1. Normative References
[RFC1122] Braden, R. (ed.), "Requirements for Internet Hosts:
Communication Layers, " STD 3, RFC 1122, Oct. 1989
(STANDARD).
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997 (BEST
CURRENT PRACTICE).
[RFC4340] Kohler, E., M. Handley, S. Floyd, "Datagram Congestion
Control Protocol (DCCP)", RFC 4340, Mar. 2006 (PROPOSED
STANDARD).
12.2. Informative References
[IANA] Internet Assigned Numbers Authority, www.iana.org
[IANA-SC] IANA DCCP Service Code Registry
http://www.iana.org/assignments/service-codes
[ID.Portnames] J. Touch, "A TCP Option for Port Names", IETF Work in
Progress, draft-touch-tcp-portnames-00.txt.
[ID.DTLS.DCCP] T.Phelan, "Datagram Transport Layer Security (DTLS)
over the Datagram Congestion Control Protocol (DCCP)", IETF
Work in Progress, draft-phelan-dccp-dtls-xx.txt.
[ID.DCCP.RTP] C. Perkins, "RTP and the Datagram Congestion Control
Protocol (DCCP)", IETF Work in Progress, draft-ietf-dccp-
rtp-xx.txt.
[ID.TSVWG.RAND] M. Larsen, F. Gont, "Port Randomization", IETF Work
in Progress, draft-larsen-tsvwg-port-randomization-00.
[iperf] http://dast.nlanr.net/Projects/Iperf/
[RFC768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, Sept. 1981 (STANDARD).
[RFC814] Clark, D., "NAME, ADDRESSES, PORTS, AND ROUTES", RFC 814,
July 1982 (UNKNOWN).
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[RFC862] Postel, J., "Echo Protocol", STD 20, RFC 862, May 1983.
[RFC864] Postel, J., "Character Generator Protocol", STD 22, RFC
864, May 1983.
[RFC867] Postel, J., "Daytime Protocol", STD 25, RFC 867, May 1983.
[RFC868] Postel, J. and K. Harrenstien, "Time Protocol", STD 26,
RFC 868, May 1983.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC 2663,
August 1999.
[RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address Translation
- Protocol Translation (NAT-PT)", RFC 2766, February 2000.
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", BCP
37, RFC 2780, March 2000.
[RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Zhang,
L., and V. Paxson, "Stream Control Transmission Protocol",
RFC 2960, October 2000.
[RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993,
November 2000.
[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, February 2002.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6", RFC
3493, February 2003.
[RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and
G. Fairhurst, "The Lightweight User Datagram Protocol (UDP-
Lite)", RFC 3828, July 2004.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4347] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
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13. Author's Addresses
Godred (Gorry) Fairhurst
Department of Engineering
University of Aberdeen
Kings College
Aberdeen, AB24 3UE
UK
Email: gorry@erg.abdn.ac.uk
URL: http://www.erg.abdn.ac.uk/users/gorry
13.1. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
13.2. Disclaimer of Validity
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.
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13.3. Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
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APPENDIX A: Informative Examples of Host Configuration
>>> The author would particularly welcome comments on this draft
section
The IETF does not normally define the formats used by implementers to
store configuration data. The following example is therefore
illustrative, and not a normative definition of how this should be
done.
In the example below, an implementation uses the /etc/services format
widely used in UNIX, but provides an additional field to specify the
service code value permitted:
An example could be:
discard 9/dccp/DISC
This raises the question of how to permit multiple Service Codes for
the same port, which could be introduced as:
discard 9/dccp/DISC
fpp 9/dccp/fdpz
Where ffp is a hypothetical example of an application using the
Service Code: fpdz, that has the same port as PERF. In this example,
PERF is defined first and would be the default association.
One drawback of this approach is that a Service Code could be
associated with a range of port values, (e.g. when used to identify
RTP sessions). The above syntax would require one line for each
possible port number, which is not compact.
An alternative is therefore to define a file format that separately
specified Service Codes and the range of Port Numbers that are
permitted.
>>> Can we recommend just one method?
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>>> RFC Editor please remove this section prior to publication.
Change Log.
01 introduced:
- a replacement of the word *range* when referring to sets of dccp
ports (they are not necessarily contiguous), noted by E. Kohler.
- Addition of some Service Codes in IANA section.
02 introduced:
- add the use of profiles with DCCP, identified by Service Code, but
not the use of protocol variants.
- further detail on implementation levels (more input would be good)
- added security consideration for traffic generators
- added ref to UDPL for completeness
- Corrected NiTs found by Gerrit Renker
+++++++++++++++++++++++++++
WG 00 (first WG version)
This introduced revisions to make it a WG document.
- Corrected language and responded to many helpful comments from
Fernando Gont and Ian McDonald.
- Added a test for which server behaviour is used.
- Added some speculative text on how to implement the SC.
- More input and discussion is requested from the WG.
- Added an informative appendix on host configuration.
- Merging of some sections to remove repetition and clarify wording.
+++++++++++++++++++++++++++
RFC4340 states (Service Codes are not intended to be DCCP-specific
and are allocated by IANA.)
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