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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 6587

Network Working Group                                        R. Gerhards
Internet-Draft                                              Adiscon GmbH
Intended status: Informational                                C. Lonvick
Expires: January 27, 2012                             Cisco Systems, Inc
                                                           July 26, 2011


                Transmission of Syslog Messages over TCP
                 draft-gerhards-syslog-plain-tcp-09.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.
   The aim of this specification is to explain how TCP has been used as
   a transport for syslog messages.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on January 27, 2012.

Copyright Notice

   Copyright (c) 2011 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
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  5
   3.  Message Transmission . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Session  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Session Initiation . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Message Transfer . . . . . . . . . . . . . . . . . . . . .  6
       3.3.1.  Octet Counting . . . . . . . . . . . . . . . . . . . .  6
       3.3.2.  Octet Stuffing . . . . . . . . . . . . . . . . . . . .  7
       3.3.3.  Method Change  . . . . . . . . . . . . . . . . . . . .  7
     3.4.  Session Closure  . . . . . . . . . . . . . . . . . . . . .  7
   4.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  Notes to the RFC Editor and Change Log . . . . . . . . . . . .  9
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  Normative  . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.2.  Informative  . . . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11





















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1.  Introduction

   Historically, the syslog protocol [RFC3164] has been run over UDP.
   This has been replaced with the standardized syslog protocol
   [RFC5424] in which the TLS transport [RFC5425] is required.  Even so,
   there are many instances of syslog running atop TCP [RFC0793].

   Two primary format options have been observed with legacy syslog
   being transported over TCP.  These have been called octet-stuffing
   and octet-counting.  The octet-stuffing 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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2.  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".


3.  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.

3.1.  Session

   A syslog over TCP session is a TCP connection between a syslog
   transport sender and a syslog transport receiver.  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.

   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.

3.2.  Session Initiation

   The TCP host that intends to act as a syslog transport receiver
   listens to TCP port <TBD>.  The TCP host that intends to act as the
   transport sender initiates a TCP session to the syslog transport
   receiver as specified in [RFC0793].





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3.3.  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 octet-stuffing has problems.  The newer method of octet-
   counting is reliable and is usually preferred.

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

3.3.1.  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 assume 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

       SP = %d32

       NONZERO-DIGIT = %d49-57

       DIGIT = %d48 / NONZERO-DIGIT

       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.




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3.3.2.  Octet Stuffing

   The octet stuffing 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 USASCII LF (%d10).  However,
   other characters have also been seen, with USASCII 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 octet-stuffing 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
   receiving syslog application.

   The ABNF for this is shown here:

       TCP-DATA = *SYSLOG-FRAME

       SYSLOG-FRAME = SYSLOG-MSG TRAILER     ; Octet-stuffing method

       TRAILER = LF | APP-DEFINED

       LF = %d10

       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 octet-stuffing framing is used
   if a syslog frame starts with the USASCII character "<" (%d60).

3.3.3.  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.

3.4.  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.



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4.  Applicability Statement

   As per the standards track documents in the syslog series, it is
   recommended to use the TLS transport [RFC5425] to transport syslog
   messages.  This document is provided to document what has been seen
   in hopes that interoperability for transporting syslog over TCP may
   be achieved.

   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.


5.  Security Considerations

   Even though it is recommended to use the TLS transport [RFC5425] to
   convey syslog messages, it is expected that people will still use the
   TCP transport.

   Several syslog security considerations are discussed in [RFC5424].
   This section focuses on security considerations specific to the
   syslog transport over TCP.  Some of the security issues raised in
   this section can be mitigated through the use of TLS as defined in
   [RFC5425]

   It should be noted that the syslog transport specified in this
   document does not use application-layer acknowledgments.  TCP uses
   retransmissions to provide protection against some forms of data
   loss.  However, if the TCP connection is broken for some reason (or
   closed by the transport receiver), the syslog transport sender cannot
   always know what messages were successfully delivered to the syslog
   application at the other end.

   Implementors should be aware of vulnerabilities in the transport
   layer that they choose.  In some cases, these vulnerabilities will be
   in the implementation, such as in the case of the UDP checksum error
   [RFC1122].  In other cases, the vulnerability will be in the
   specification, such as in the case of the SSL/TLS renegotiation as



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   described in [RFC5746].  Specific to this transport, implementers may
   wish to review any known vulnerabilities of TCP prior to writing
   code.  A good start to this investigation may be found in an article
   by Steve Bellovin in the Association for Computing Machinery (ACM)
   publication [Bellovin].


6.  IANA Considerations

   IANA is requested to provide a TCP port for this protocol.

   After that port has been assigned, this section will be revised to
   list that port.


7.  Acknowledgments

   The authors wish to thank David Harrington, Tom Petch, Richard
   Graveman, and all other people who commented on various versions of
   this proposal.


8.  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.

   Please replace the instances of <TBD> with the port number assigned
   by IANA.

   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



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   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
   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.


9.  References

9.1.  Normative

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

   [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.

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

9.2.  Informative

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

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

   [RFC5746]  Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
              "Transport Layer Security (TLS) Renegotiation Indication



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              Extension", RFC 5746, February 2010.

   [Bellovin]
              Bellovin, S., "Security problems in the TCP/IP protocol
              suite, ACM SIGCOMM Computer Communication Review, Volume
              19 Issue 2", April 1989.


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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