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No home yet                                                  R. Gerhards
Internet-Draft                                              Adiscon GmbH
Expires: June 3, 2010                                         C. Lonvick
                                                      Cisco Systems, Inc
                                                       November 30, 2009


                Transmission of Syslog Messages over TCP
                 draft-gerhards-syslog-plain-tcp-00.txt

Abstract

   This document describes the transport for syslog messages over TCP/
   IPv4 or TCP/IPv6.  The syslog protocol layered architecture provides
   for support of any number of transport mappings.  However, for
   interoperability purposes, syslog protocol implementers are required
   to support this transport mapping.

   There have been many implementations and deployments of traditional
   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 document three things: how to
   transmit standardized syslog over TCP, how this has been done for
   traditional syslog, and how the new syslog architecture can
   interoperate with the traditional deployments.

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
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   Drafts.

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   time.  It is inappropriate to use Internet-Drafts as reference
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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.



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   This Internet-Draft will expire on June 3, 2010.

Copyright Notice

   Copyright (c) 2009 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
   described in the BSD License.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
   3.  Message Transmission . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Session  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Session Initiation . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Message Transfer . . . . . . . . . . . . . . . . . . . . .  5
       3.3.1.  Octet-Stuffing . . . . . . . . . . . . . . . . . . . .  7
       3.3.2.  Octet-Counting . . . . . . . . . . . . . . . . . . . .  7
     3.4.  Message Content  . . . . . . . . . . . . . . . . . . . . .  7
     3.5.  Session Closure  . . . . . . . . . . . . . . . . . . . . .  8
   4.  Applicability to Legacy syslog . . . . . . . . . . . . . . . .  8
     4.1.  Method Change  . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Octet-Counting . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  Octet Stuffing . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     5.1.  Sender Authentication and Message Forgery  . . . . . . . .  9
     5.2.  Message Observation  . . . . . . . . . . . . . . . . . . . 10
     5.3.  Replaying  . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Message Prioritization and Differentiation . . . . . . . . 10
     5.5.  Denial of Service  . . . . . . . . . . . . . . . . . . . . 10
     5.6.  Reliability  . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  Authors  . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 11
   9.  Notes to the RFC Editor  . . . . . . . . . . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1. Normative  . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.2. Informative  . . . . . . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12




















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1.  Introduction

   The syslog protocol [RFC5424] is a text-based protocol used to convey
   event information.  Before that standard was produced, syslog
   messages were being transmitted over UDP.  This was described in the
   INFORMATIONAL document [RFC3164].  While there has been no documented
   standard for transporting syslog messages over TCP, it is widely used
   in practice and has proven to be quite interoperable among the
   implementations, with some minor issues in some configurations.
   While existing implementations interoperate quite well with each
   other, there are some differences in protocol handling.  This
   document will describe the most commonly used approach and explain
   how to interoperate with them in a consistent way.

   This specification applies to messages transmitted using the
   [RFC5424] format.  A discussion of how this may be applied to
   [RFC3164] messages is contained below.  This specification is written
   this way, with two format options, in an attempt to ensure that
   syslog transport receivers can receive and properly interpret
   messages sent from legacy syslog senders.

   It is still RECOMMENDED to use the TLS transport [RFC5424] to convey
   syslog messages.  This specification is provided to ensure
   interoperability for transporting syslog over TCP.


2.  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].

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


3.  Message Transmission

   As described in [RFC5424], syslog is simplex in nature.  Traditional
   TCP implementations 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.  Reliability and flow control are provided by the
   abilities of TCP.






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3.1.  Session

   A syslog over TCP session is a TCP connection between a client and a
   server.  The syslog transport sender is the host that sends the
   original SYN.  The syslog transport receiver is the device that
   receives the original SYN and responds with a SYN+ACK.  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 are fixed once the session is
   established, and they can not be reversed during the session.
   However, there can be multiple sessions between two TCP hosts, and
   for each session the role of transport sender and transport receiver
   can be different based upon which device initiates the session.

                    |
                    +<--------------------------+
                    |                           |
                    V                           |
           +------------------+                 |
           | session initiate |                 |
           +------------------+                 |
              |     | success                   |
       +------+     |                           |
       |shutdown    |  +------------+           |
       |failure     V  V            |           |
       |   +------------------+     | more      |
       |   |   send message   |     | messages  |
       |   +------------------+     |           |
       |            |  |            |           |
       |            |  +------------+           |
       +--------+   | failure                   |
                |   | shutdown decision         |
                V   V                           |
           +------------------+                 |
           | session closure  |                 |
           +------------------+                 |
                    |        re-init            |
                    +---------------------------+

   Diagram 1.  Transport Sender State Machine










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                    |
                    +<--------------------------+
                    |                           |
                    V                           |
           +------------------+                 |
           |listen for connect|                 |
           +------------------+                 |
              |     | success                   |
       +------+     |                           |
       |shutdown    |  +------------+           |
       |failure     V  V            |           |
       |   +------------------+     | more      |
       |   | receive message  |     | messages  |
       |   +------------------+     |           |
       |            |  |            |           |
       |            |  +------------+           |
       +--------+   | failure                   |
                |   | shutdown decision         |
                V   V                           |
           +------------------+                 |
           | session closure  |                 |
           +------------------+                 |
                    |        re-init            |
                    +---------------------------+

   Diagram 1.  Transport Receiver State Machine

   A syslog transport sender is a simple state machine as shown in
   diagram 1.  A transport receiver is a simple state machine as shown
   in diagram 2.  It is valid (but rare) for no messages to be exchanged
   during a TCP session.

   Note the absence of any real error processing on the state machine.
   If an error occurs, the peer detecting the error will gracefully
   close the TCP session, but has no means to notify its remote peer
   about the state of the peer syslog application.

3.2.  Session Initiation

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

3.3.  Message Transfer

   During the message transfer phase, the syslog transport sender sends
   a stream of messages to the transport receiver.  Either of the peers



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

   Syslog messages are sent in sequence within a TCP transport stream.
   At least one message is encapsulated inside a frame.  Transport
   senders use one of two different framing formats.  They MUST support
   the octect-counting method and they MAY support the octet-stuffing
   method.  Syslog transport receivers are REQUIRED to support the
   octet-counting method and are RECOMMENDED to support the octet-
   stuffing method to promote interoperability with legacy devices that
   may only use that framing method.  Transport senders do not send any
   notice about the format they use to the transport receiver.  However,
   the format itself enables the transport receiver to detect which
   framing is used.  The syslog transport sender MUST NOT change the
   format after it has sent the first message.  If the format needs to
   be changed, the TCP session must be concluded and a new session
   established.

   The syslog message stream has the following ABNF [RFC5234]
   definition:


       APPLICATION-DATA = *SYSLOG-FRAME

       SYSLOG-FRAME = SYSLOG-MSG TRAILER
       SYSLOG-FRAME =/ MSG-LEN SP SYSLOG-MSG

       MSG-LEN = NONZERO-DIGIT *DIGIT

       SP = %d32

       NONZERO-DIGIT = %d49-57

       DIGIT = %d48 / NONZERO-DIGIT

       TRAILER = LF | APP-DEFINED

       LF = %d10

                                 Figure 1

   Note that APP-DEFINED is not specified inside the ABNF and is used as
   a placeholder for slightly different terminators found in practice.







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3.3.1.  Octet-Stuffing

   In octet-stuffing mode, there is no header, but a trailer is appended
   after SYSLOG-MSG.  For this specification, this character MUST be the
   USASCII LF (%d10) character.

   A transport receiver MUST accept that the TRAILER character is a
   USASCII LF.  It MAY be configurable to accept other characters.  A
   discussion of this may be found below.

   It is recommended, and is current practice, that a transport receiver
   assumes that octet-stuffing framing is used if a syslog frame starts
   with the USASCII character "<" (%d60).

   The octect-stuffing method is NOT RECOMMENDED.

3.3.2.  Octet-Counting

   This mode is somewhat similar to the framing used in [RFC5425].  Here
   the message length, in octets, is specified as HEADER, followed by
   SYSLOG-MSG and no trailer.

   MSG-LEN is the octet count of the SYSLOG-MSG in the SYSLOG-FRAME.  A
   transport receiver MUST use the message length to delimit a syslog
   message.  There is no upper limit for a message length per se.
   However, in order to establish a baseline for interoperability, this
   specification requires that a transport receiver MUST be able to
   process messages with a length up to and including 2048 octets.
   Transport receivers SHOULD be able to process messages with lengths
   up to and including 8192 octets.

   It is recommended and current practice that a transport receiver
   assumes that octet counted framing is used if a syslog frame starts
   with a digit.

3.4.  Message Content

   SYSLOG-MSG is defined in [RFC5424].  Most senders use the format
   described in [RFC3164] as an alternate format.

   The syslog transport receiver MUST discard the TRAILER as it accepts
   the packet.  That is to say that if the TRAILER character is kept
   with the message, then the message received will not be what was
   sent, and it will also no longer be compliant with the format
   specified in [RFC5424]






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3.5.  Session Closure

   The SYSLOG session is closed when one of the peers decides to do so.
   It then initiates a TCP session closure.  It does not notify its
   remote peer of its intension to close the session, nor does it accept
   any messages that are still in transit.


4.  Applicability to Legacy syslog

   This is an informative section provided to promote interoperability
   within the various observed implementations.  Even though this
   specification does not cover legacy syslog messages, the language
   used here will be consistent with [RFC2119] to be clear in this and
   to show how the new syslog architecture will interoperate with the
   legacy implementations.

   Syslog over TCP has been around for a number of years.  Just like
   traditional syslog, several different implementations exist.  The
   older method of octet-stuffing has problems so implementers are
   encouraged to not use that mechanism.  The newer method of octect-
   counting is reliable and should be used.

   It is recommended and current practice that a transport receiver
   assumes that octet-counting framing is used if a syslog frame starts
   with a digit.

4.1.  Method Change

   It has been observed in legacy implementations that the framing may
   change on a frame-by-frame basis.  That is to say that a transport
   receiver SHOULD be prepared to accept different framing for each
   frame received.  Devices that wish to interoperate with these legacy
   systems should be aware of this.

4.2.  Octet-Counting

   This framing allows for the transmission of all characters inside
   SYSLOG-MSG.  Some transport senders have been seen to use this
   framing to stack multiple messages within a single TCP frame.

   This method is REQUIRED for syslog transport receivers and senders.

4.3.  Octet Stuffing

   The problem with octet-stuffing framing comes from the use of
   [RFC3164] messages.  In that the traditional trailer character is not
   escaped within SYSLOG-MSG which causes problems for the receiver.



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   For example, a message in the style of [RFC3164] containing one or
   more LF characters may be misinterpreted as multiple messages by the
   transport receiver.  There is no method to avoid this problem with
   the octet-stuffing framing.

   In this legacy implementation, the TRAILER consists of a single
   character and most often is the USASCII LF (%d10) character.
   However, other characters have also been seen occasionally, with
   USACII NUL (%d00) being a prominent example.  Some devices also emit
   a two-character TRAILER, which is usually CR and LF. i

   Transport senders MUST support the option to use the USASCII LF
   character.  Transport receivers MUST also support this.  Transport
   senders and receivers MAY also support other characters.


5.  Security Considerations

   Using this specification on an unsecured network is NOT RECOMMENDED.
   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]

5.1.  Sender Authentication and Message Forgery

   This transport mapping does not provide for strong sender
   authentication.  The receiver of the syslog message will not be able
   to ascertain that the message was indeed sent from the reported
   sender, or whether the packet was sent from another device.  This can
   also lead to a case of mistaken identity if an inappropriately
   configured machine sends syslog messages to a receiver representing
   itself as another machine.

   This transport mapping does not provide protection against syslog
   message forgery.  An attacker can transmit syslog messages (either
   from the machine from which the messages are purportedly sent or from
   any other machine) to a receiver.

   In one case, an attacker can hide the true nature of an attack amidst
   many other messages.  As an example, an attacker can start generating
   forged messages indicating a problem on some machine.  This can get
   the attention of the system administrators, who will spend their time
   investigating the alleged problem.  During this time, the attacker
   could be able to compromise a different machine or a different
   process on the same machine.




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   Additionally, an attacker can generate false syslog messages to give
   untrue indications of the status of systems.  As an example, an
   attacker can stop a critical process on a machine, which could
   generate a notification of exit.  The attacker can subsequently
   generate a forged notification that the process had been restarted.
   The system administrators could accept that misinformation and not
   verify that the process had indeed not been restarted.

5.2.  Message Observation

   This transport mapping does not provide confidentiality of the
   messages in transit.  If syslog messages are in clear text, this is
   how they will be transferred.  In most cases, passing clear-text,
   human-readable messages is a benefit to the administrators.
   Unfortunately, an attacker could also be able to observe the human-
   readable contents of syslog messages.  The attacker could then use
   the knowledge gained from these messages to compromise a machine.  It
   is RECOMMENDED that no sensitive information be transmitted via this
   transport mapping or that transmission of such information be
   restricted to properly secured networks.

5.3.  Replaying

   Message forgery and observation can be combined into a replay attack.
   An attacker could record a set of messages that indicate normal
   activity of a machine.  At a later time, an attacker could remove
   that machine from the network and replay the syslog messages with new
   time stamps.  The administrators could find nothing unusual in the
   received messages, and their receipt would falsely indicate normal
   activity of the machine.

5.4.  Message Prioritization and Differentiation

   This transport mapping does not mandate prioritization of syslog
   messages either on the wire or when processed on the receiving host
   based on their severity.  Unless some prioritization is implemented
   by sender, receiver, and/or network, the security implication of such
   behavior is that the syslog receiver or network devices could get
   overwhelmed with low-severity messages and be forced to discard
   potentially high-severity messages.

5.5.  Denial of Service

   An attacker could overwhelm a receiver by sending more messages to it
   than could be handled by the infrastructure or the device itself.
   Implementers SHOULD attempt to provide features that minimize this
   threat, such as optionally restricting reception of messages to a set
   of known source IP addresses.



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5.6.  Reliability

   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.


6.  Authors

   The authors of this draft are:


         Rainer Gerhards

         Adiscon GmbH
         Mozartstrasse 21
         97950 Grossrinderfeld
         Germany

         Email: rgerhards@adiscon.com


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

         EMail: clonvick@cisco.com



7.  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.


8.  Acknowledgments

   This document was written using the xml2rfc tool described in RFC2629
   [RFC2629].



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   The authors wish to thank and all other people who commented on
   various versions of this proposal.


9.  Notes to the RFC Editor

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

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


10.  References

10.1.  Normative

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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

10.2.  Informative

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

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












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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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