


Network Working Group                                        R. Gerhards
Internet-Draft                                              Adiscon GmbH
Intended status: Historic                                     C. Lonvick
Expires: August 14, 2012                             Cisco Systems, Inc.
                                                       February 11, 2012


                Transmission of Syslog Messages over TCP
                 draft-gerhards-syslog-plain-tcp-14.txt

Abstract

   There have been many implementations and deployments of legacy syslog
   over TCP for many years.  That protocol has evolved without being
   standardized and has proven to be quite interoperable in practice.
   This memo describes how TCP has been used as a transport for syslog
   messages.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on August 14, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Statement by the IESG  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Conventions Used in This Document  . . . . . . . . . . . . . .  5
   4.  Message Transmission . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Character Encoding Scheme  . . . . . . . . . . . . . . . .  5
     4.2.  Session  . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.3.  Session Initiation . . . . . . . . . . . . . . . . . . . .  6
     4.4.  Message Transfer . . . . . . . . . . . . . . . . . . . . .  6
       4.4.1.  Octet Counting . . . . . . . . . . . . . . . . . . . .  7
       4.4.2.  Non-Transparent-Framing  . . . . . . . . . . . . . . .  7
       4.4.3.  Method Change  . . . . . . . . . . . . . . . . . . . .  8
     4.5.  Session Closure  . . . . . . . . . . . . . . . . . . . . .  8
   5.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  Notes to the RFC Editor and Change Log . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     10.1. Normative  . . . . . . . . . . . . . . . . . . . . . . . . 11
     10.2. Informative  . . . . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

























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1.  Statement by the IESG

   The IESG does not recommend implementing or deploying syslog over
   plain tcp, which is described in this document, because it lacks the
   ability to enable strong security [RFC3365].

   The TLS transport [RFC5425] is recommended for implementation so that
   appropriate security features are available to operators who want to
   deploy secure syslog.  Similarly, those security features can be
   turned off for those who do not want them.


2.  Introduction

   The standards track documents in the syslog series recommend using
   the syslog protocol [RFC5424] with the TLS transport [RFC5425] for
   all event messages.  The authors of this document wholeheartedly
   support that position and only offer this document to describe what
   has been observed with legacy syslog over TCP, which appears to still
   be widely used.

   Two primary format options have been observed with legacy syslog
   being transported over TCP.  These have been called non-transparent-
   framing and octet-counting.  The non-transparent-framing mechanism
   has some inherent problems.

   Diagram 1 shows how all of these syslog transports relate to each
   other.  In this diagram three originators are seen, labeled A, B, and
   C, along with one collector.  Originator A is using the TCP transport
   which is described in this document.  Originator B is using the UDP
   transport, which is described in [RFC5426].  Originator C is using
   the TLS transport, which is described in [RFC5425].  The collector is
   shown with the capability to accept all three transports.


















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    +---------------------+
    | Originator A        |
    |---------------------|
    |  syslog application |
    |                     |
    |---------------------|
    |  syslog transport   |
    |        TCP          |
    |---------------------|
              v
              |
             /                            +---------------------+
            /                             | Originator B        |
           /                              |---------------------|
          /   +----------------------+    |  syslog application |
         /    | Collector            |    |                     |
        |     |----------------------|    |---------------------|
        |     |  syslog application  |    |  syslog transport   |
        |     |                      |    |        UDP          |
        |     |----------------------|    |---------------------|
        |     |  syslog transport    |              v
        |     |  TCP |  TLS  |  UDP  |              |
        |     |----------------------|              |
        |         ^      ^       ^                  |
        |         |      |       |                  |
        \         /      |       \                  /
         ---------       |        ------------------
                         |
                         |
                         |     +---------------------+
                         |     | Originator C        |
                         |     |---------------------|
                         |     |  syslog application |
                         |     |                     |
                         |     |---------------------|
                         |     |  syslog transport   |
                         |     |        TLS          |
                         |     |---------------------|
                         |               v
                         \               /
                          ---------------

                Diagram 1.  Syslog Layers








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3.  Conventions Used in This Document

   The terminology defined in Section 3 of [RFC5424] is used throughout
   this specification.  The reader should be familiar with that to
   follow this discussion.

   This document also references devices that use the syslog message
   format as described in [RFC3164].  Devices that continue to use that
   message format (regardless of transport) will be described as "legacy
   syslog devices".  Similarly, devices that use the message format as
   described in [RFC5424] will be described as "standardized syslog
   devices".


4.  Message Transmission

   Syslog is simplex in nature.  It has been observed that
   implementations of syslog over TCP also do not use any backchannel
   mechanism to convey information to the transport sender, and
   consequently do not use any application-level acknowledgement for
   syslog receiver to sender signaling.  Message receipt
   acknowledgement, reliability, and flow control are provided by the
   capabilities of TCP.

4.1.  Character Encoding Scheme

   Syslog over TCP messages contain no indication of the coded character
   set (e.g., [US-ASCII] or [UNICODE] ) or character encoding scheme
   (e.g., so-called "7-bit ASCII" or UTF-8 [RFC3629]) in use.  In these
   messages, the predominant approach has been to include characters
   only from the ASCII repertoire (i.e., %d32 to %d126 inclusive) using
   the "Network Virtual Terminal" (NVT) encoding [RFC5198].

   The message header usually contains characters only from the ASCII
   repertoire, in the NVT encoding.  This has been observed even in
   cases where a different encoding (e.g., UTF-8) has been used for the
   MSG part.  However, characters outside the ASCII range have been seen
   inside the header.  In that case, some syslog applications have been
   known to experience problems processing those messages.

   In some cases, it has been observed that characters outside of the
   ASCII range are often being transformed by receivers in an effort to
   "escape control characters".  Some receiver implementations simply
   drop those characters.  This is considered to be a poor practice as
   it causes problems with coded character sets other than ASCII and
   character encodings other than NVT, most notably the UTF-8 encoding
   of Unicode.




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   It has also been observed that relays will forward messages using the
   character encoding schemes of messages they receive.  In the case
   where two different senders are using different character encoding
   schemes, the relay will forward each message to a collector in that
   character encoding.  The collector of these messages will have to be
   prepared to receive messages from the same relay with different
   encodings.

4.2.  Session

   Like most other protocols, the syslog transport sender is the TCP
   host that initiates the TCP session.  After initiation, messages are
   sent from the transport sender to the transport receiver.  No
   application-level data is transmitted from the transport receiver to
   the transport sender.  The roles of transport sender and receiver
   seem to be fixed once the session is established.

   When it has been observed, if an error occurs that cannot be
   corrected by TCP, the host detecting the error gracefully closes the
   TCP session.  There have been no application level messages seen that
   were sent to notify the other host about the state of the host syslog
   application.

4.3.  Session Initiation

   The TCP host acting as a syslog transport receiver listens to a TCP
   port.  The TCP transport sender initiates a TCP session to the syslog
   transport receiver as specified in [RFC0793].

   This protocol has no standardized port assignment.  In practice,
   network administrators generally choose something that they feel will
   not conflict with anything else active in their networks.  This has
   most often been either TCP/514, which is actually allocated to
   another protocol, or some variant of adding 514 to a multiple of
   1000.  Please see Section 5 for more information about this.

4.4.  Message Transfer

   Syslog over TCP has been around for a number of years.  Just like
   legacy syslog over UDP, different implementations exist.  The older
   method of non-transparent-framing has problems.  The newer method of
   octet-counting is reliable and has not been seen to cause problems
   noted with the non-transparent-framing method.

   In both of these methods, during the message transfer phase, the
   syslog transport sender sends a stream of messages to the transport
   receiver.  These are sent in sequence and one message is encapsulated
   inside each TCP frame.  Either of the TCP hosts may initiate session



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   closure at any time as specified in Section 3.5 of [RFC0793].  In
   practice, this is often seen after a prolonged period of inactivity.

4.4.1.  Octet Counting

   This framing allows for the transmission of all characters inside a
   syslog message and is similar to the method used in [RFC5425].  A
   transport receiver uses the defined message length to delimit a
   syslog message.  As noted in [RFC3164] the upper limit for a legacy
   syslog message length is 1024 octets.  That length has been expanded
   for standardized syslog.

   It can be assumed that octet-counting framing is used if a syslog
   frame starts with a digit.

   All syslog messages can be considered to be TCP "data" as per
   Transmission Control Protocol [RFC0793].  The syslog message stream
   has the following ABNF [RFC5234] definition:

       TCP-DATA = *SYSLOG-FRAME

       SYSLOG-FRAME = MSG-LEN SP SYSLOG-MSG   ; Octet-counting
                                              ; method

       MSG-LEN = NONZERO-DIGIT *DIGIT

       NONZERO-DIGIT = %d49-57

       SYSLOG-MSG is defined in the syslog protocol [RFC5424] and may
                  also be considered to be the payload in [RFC3164]


   MSG-LEN is the octet count of the SYSLOG-MSG in the SYSLOG-FRAME.

4.4.2.  Non-Transparent-Framing

   The non-transparent-framing method inserts a syslog message into a
   frame and terminates it with a TRAILER character.  The TRAILER has
   usually been a single character and most often is ASCII LF (%d10).
   However, other characters have also been seen, with ASCII NUL (%d00)
   being a prominent example.  Some devices have also been seen to emit
   a two-character TRAILER, which is usually CR and LF.

   The problem with non-transparent-framing comes from the use of a
   TRAILER character.  In that, the traditional trailer character is not
   escaped within the message, which causes problems for the receiver.
   For example, a message in the style of [RFC3164] containing one or
   more LF characters may be misinterpreted as multiple messages by the



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   receiving syslog application.

   The ABNF for this is shown here:

       TCP-DATA = *SYSLOG-FRAME

       SYSLOG-FRAME = SYSLOG-MSG TRAILER  ; non-transparent-framing
                                          ; method

       TRAILER = LF / APP-DEFINED

       APP-DEFINED = 1*2OCTET

       SYSLOG-MSG is defined in the syslog protocol [RFC5424] and may
                  also be considered to be the payload in [RFC3164]


   A transport receiver can assume that non-transparent-framing is used
   if a syslog frame starts with the ASCII character "<" (%d60).

4.4.3.  Method Change

   It has been observed in legacy implementations that the framing may
   change on a frame-by-frame basis.  This is probably not a good idea,
   but it's been seen.

4.5.  Session Closure

   The syslog session is closed when one of the TCP hosts decides to do
   so.  It then initiates a local TCP session closure.  Following TCP
   [RFC0793] it doesn't need to notify the remote TCP host of its
   intention to close the session, nor does it accept any messages that
   are still in transit.


5.  Applicability Statement

   Again it must be emphasized that the standards track documents in the
   syslog series recommend using the TLS transport [RFC5425] to
   transport syslog messages.  This document does not recommend that new
   implementations or deployments use syslog over TCP except for the
   explicit purpose of interoperating with existing deployments.

   One of the major problems with interoperability with this protocol is
   that there is no consistent TCP port assigned.  Most of the
   successful implementations have made the selection of a port a user-
   configurable option.  The most frequently observed port for this has
   been TCP/514, which is actually assigned to the Shell protocol.



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   Operators must carefully select which port to use in their deployment
   and be prepared to encounter different default port assignments in
   implementations.

   There are several advantages to using TCP: flow control, error
   recovery, and reliability, to name a few.  These reasons and the ease
   of programming have lead people to use this transmission protocol to
   transmit syslog.

   One potential disadvantage is the buffering mechanism used by TCP.
   Ordinarily, TCP decides when enough data has been received from the
   application to form a segment for transmission.  This may be adjusted
   through timers but still, some application data may wait in a buffer
   for a relatively long time.  Syslog data is not normally time-
   sensitive but if this delay is a concern, the syslog transport sender
   may utilize the PUSH Flag as described in [RFC0793] to have the
   sending TCP immediately send all buffered data.


6.  Security Considerations

   This protocol makes no meaningful provisions for security.  It lacks
   authentication, integrity checking, and privacy.  It makes no
   provision for flow control or end-to-end confirmation of receipt,
   relying instead on the underlying TCP implementations to approximate
   these functions.  It should not be used if deployment of [RFC5425] on
   the systems in question is feasible.


7.  IANA Considerations

   There are no requests for IANA actions in this document.


8.  Acknowledgments

   The authors wish to thank David Harrington, Tom Petch, Richard
   Graveman, and all other people who commented on various versions of
   this proposal.  We would also like to thank Peter Saint-Andre for
   clarifying character encodings.

   The authors would also like to thank Randy Presuhn for being our
   reviewer and document shepherd, and a special thanks to Dan Romascanu
   for his support and guidance.







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9.  Notes to the RFC Editor and Change Log

   These are notes to the RFC editor.  Please delete this section after
   the notes have been followed.

   Version -14 addresses the final few IESG requests.  It was submitted
   in February of 2012.

   Version -13 addressed the IESG reviews and is changed to Historic.
   It was submitted in January of 2012.

   Version -12 addressed AD Review comments as well as GENART comments.
   It was submitted in December of 2011.

   Version -11 fixed the ABNF and was submitted in October of 2011.

   Version -10 was put together based on Randy Presuhn's feedback as
   shepherd.  A section on character sets has been added.  The term
   "octet-stuffing" was incorrectly used and has been replaced by "non-
   transparent-framing".  The security considerations section has been
   simplified.  It was submitted in October of 2011.

   Version -09 was put together based on IESG member feedback.  The
   appendixes were removed and things were consolidated to be more
   appropriate for an informational document.  It was submitted in
   August of 2011.  Dan Romascanu is actually the IESG member who will
   watch this document.

   Version -08 included a reference to vulnerabilities of TCP.  It was
   submitted in February of 2011.

   Version -07 was submitted in January, 2011.  This clarified what was
   really expected from what was optional.  Appendix B was added for
   further clarification.  Additionally, the security Considerations
   section was edited to include a discussion about transport layer
   issues.

   Version -06 was submitted in October, 2010.  The 2119 language was
   removed.  Also, we compared notes and couldn't find any
   implementations that stacked multiple messages in a frame in the
   octet-counting method.  That paragraph was removed.

   Version -05 was submitted in September, 2010 to address some items
   that David Harrington noted as he is becoming the document shepherd.

   Version -04 was submitted in April, 2010 to clean up some items.

   Version -03 was submitted in April, 2010 based upon further review



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   comments from Tom Petch.

   Version -02 was submitted in March, 2010 based upon review comments
   from Tom Petch.

   Version -01 was submitted based upon review comments from David
   Harrington.

   Version -00 was created in November, 2009.


10.  References

10.1.  Normative

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC3365]  Schiller, J., "Strong Security Requirements for Internet
              Engineering Task Force Standard Protocols", BCP 61,
              RFC 3365, August 2002.

   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, March 2008.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.

   [RFC5425]  Miao, F., Ma, Y., and J. Salowey, "Transport Layer
              Security (TLS) Transport Mapping for Syslog", RFC 5425,
              March 2009.

   [US-ASCII]
              ANSI, "Coded Character Set -- 7-bit American Standard Code
              for Information Interchange, ANSI X3.4-1986", 1968.

10.2.  Informative

   [RFC3164]  Lonvick, C., "The BSD Syslog Protocol", RFC 3164,
              August 2001.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC5426]  Okmianski, A., "Transmission of Syslog Messages over UDP",
              RFC 5426, March 2009.



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   [UNICODE]  The Unicode Consortium, "The Unicode Standard, Version
              6.0"", 2010,
              <http://www.unicode.org/versions/Unicode6.0.0/>.


Authors' Addresses

   Rainer Gerhards
   Adiscon GmbH
   Mozartstrasse 21
   Grossrinderfeld, BW  97950
   Germany

   Email: rgerhards@adiscon.com


   Chris Lonvick
   Cisco Systems, Inc.
   12515 Research Blvd.
   Austin, TX  78759
   USA

   Email: clonvick@cisco.com




























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