





Network Working Group                                             D. New
Request for Comments: 3195                                       M. Rose
Category: Standards Track                   Dover Beach Consulting, Inc.
                                                           November 2001


                      Reliable Delivery for syslog

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   The BSD Syslog Protocol describes a number of service options related
   to propagating event messages.  This memo describes two mappings of
   the syslog protocol to TCP connections, both useful for reliable
   delivery of event messages.  The first provides a trivial mapping
   maximizing backward compatibility.  The second provides a more
   complete mapping.  Both provide a degree of robustness and security
   in message delivery that is unavailable to the usual UDP-based syslog
   protocol, by providing encryption and authentication over a
   connection-oriented protocol.




















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Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.    The Model  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.    The RAW Profile  . . . . . . . . . . . . . . . . . . . . . .  7
   3.1   RAW Profile Overview . . . . . . . . . . . . . . . . . . . .  7
   3.2   RAW Profile Identification and Initialization  . . . . . . .  9
   3.3   RAW Profile Message Syntax . . . . . . . . . . . . . . . . . 10
   3.4   RAW Profile Message Semantics  . . . . . . . . . . . . . . . 10
   4.    The COOKED Profile . . . . . . . . . . . . . . . . . . . . . 11
   4.1   COOKED Profile Overview  . . . . . . . . . . . . . . . . . . 11
   4.2   COOKED Profile Identification and Initialization . . . . . . 11
   4.3   COOKED Profile Message Syntax  . . . . . . . . . . . . . . . 11
   4.4   COOKED Profile Message Semantics . . . . . . . . . . . . . . 12
   4.4.1 The IAM Element  . . . . . . . . . . . . . . . . . . . . . . 12
   4.4.2 The ENTRY Element  . . . . . . . . . . . . . . . . . . . . . 14
   4.4.3 The PATH Element . . . . . . . . . . . . . . . . . . . . . . 19
   5.    Additional Provisioning  . . . . . . . . . . . . . . . . . . 25
   5.1   Message Authenticity . . . . . . . . . . . . . . . . . . . . 25
   5.2   Message Replay . . . . . . . . . . . . . . . . . . . . . . . 25
   5.3   Message Integrity  . . . . . . . . . . . . . . . . . . . . . 25
   5.4   Message Observation  . . . . . . . . . . . . . . . . . . . . 26
   5.5   Summary of Recommended Practices . . . . . . . . . . . . . . 26
   6.    Initial Registrations  . . . . . . . . . . . . . . . . . . . 27
   6.1   Registration: The RAW Profile  . . . . . . . . . . . . . . . 27
   6.2   Registration: The COOKED Profile . . . . . . . . . . . . . . 27
   7.    The syslog DTD . . . . . . . . . . . . . . . . . . . . . . . 28
   8.    Reply Codes  . . . . . . . . . . . . . . . . . . . . . . . . 32
   9.    IANA Considerations  . . . . . . . . . . . . . . . . . . . . 33
   9.1   Registration: BEEP Profiles  . . . . . . . . . . . . . . . . 33
   9.2   Registration: The System (Well-Known) TCP port number for
            syslog-conn . . . . . . . . . . . . . . . . . . . . . . . 33
   10.   Security Considerations  . . . . . . . . . . . . . . . . . . 34
   11.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34
   12.   References . . . . . . . . . . . . . . . . . . . . . . . . . 34
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 36














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1. Introduction

   The syslog protocol [1] presents a spectrum of service options for
   provisioning an event-based logging service over a network.  Each
   option has associated benefits and costs.  Accordingly, the choice as
   to what combination of options is provisioned is both an engineering
   and administrative decision.  This memo describes how to realize the
   syslog protocol when reliable delivery is selected as a required
   service.  It is beyond the scope of this memo to argue for, or
   against, the use of reliable delivery for the syslog protocol.

   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 [2].





































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2. The Model

   The syslog service supports three roles of operation: device, relay,
   and collector.

   Devices and collectors act as sources and sinks, respectively, of
   syslog entries.  In the simplest case, only a device and collector
   are present.  E.g.,

     +--------+        +-----------+
     | Device | -----> | Collector |
     +--------+        +-----------+

   The relationship between devices and collectors is potentially many-
   to-many.  I.e., a device might communicate with many collectors;
   similarly, a collector might communicate with many devices.

   A relay operates in both modes, accepting syslog entries from devices
   and other relays and forwarding those entries to collectors and other
   relays.

   For example,

     +--------+      +-------+        +-------+      +-----------+
     | Device | ---> | Relay | -...-> | Relay | ---> | Collector |
     +--------+      +-------+        +-------+      +-----------+

   As shown, more than one relay may be present between any particular
   device and collector.

   A relay may be necessary for administrative reasons.  For example, a
   relay might run as an application proxy on a firewall.  Also, there
   might be one relay per company department, which authenticates all
   the devices in the department, and which in turn authenticates itself
   to a company-wide collector.

   A relay can also serve to filter messages.  For example, one relay
   may collect the syslog information from an entire web server farm,
   summarizing hit counts for report generation, forwarding "page not
   found" messages (indicating a possible broken link) to a collector
   that presents it to the webmaster, and sending more urgent messages
   (such as hardware failure reports) to a collector that gateways them
   to a pager.  A relay may also be used to convert formats from a
   device's output to a collector's input.

   It should be noted that a role of device, relay, or collector is
   relevant only to a particular BEEP channel (q.v., below).  A single
   server can serve as a device, a relay, and a collector, all at once,



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   if so configured.  It can even serve as a relay and a collector to
   the same device at the same time using different BEEP channels over
   the same connection-oriented session; this might be useful to collect
   status yet relay urgent error messages.

   To provide reliable delivery when realizing the syslog protocol, this
   memo defines two BEEP profiles.  BEEP [3] is a generic application
   protocol framework for connection-oriented, asynchronous
   interactions.  Within BEEP, features such as authentication, privacy,
   and reliability through retransmission are provided.  There are two
   profiles defined in this memo:

   o  The RAW profile is designed to provide a high-performance, low-
      impact footprint, using essentially the same format as the
      existing UDP-based syslog service.

   o  The COOKED profile is designed to provide a structured entry
      format, in which individual entries are acknowledged (either
      positively or negatively).

   Note that both profiles run over BEEP.  BEEP defines "transport
   mappings," specifying how BEEP messages are carried over the
   underlying transport technologies.  At the time of this writing, only
   one such transport is defined, in [4], which specifies BEEP over TCP.
   All transport mappings are required to support enough reliability and
   sequencing to allow all BEEP messages on a given channel to be
   delivered reliably and in order.  Hence, both the RAW and COOKED
   profile provide reliable delivery of their messages.

   The choice of profile is independent of the operational roles
   discussed above.

   For example, in

     +--------+        +-------+        +-----------+
     | Device | -----> | Relay | -----> | Collector |
     +--------+        +-------+        +-----------+

   the device-to-relay link could be configured to use the RAW profile,
   while the relay-to-collector link could be configured to use the
   COOKED profile.  (For example, the relay may be parsing the RAW
   syslog messages from the device, knowing the details of their
   formats, before passing them to a more generic collector.) Indeed,
   the same device may use different profiles, depending on the
   collector to which it is sending entries.






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   Devices and relays MAY discover relays and collectors via the DNS SRV
   algorithm [5].  If so configured, the service used is "syslog" and
   the protocol used is "tcp".  This allows for central administration
   of addressing, fallback for failed relays and collectors, and static
   load balancing.  Security policies and hardware configurations may be
   such that device configuration is more secure than the DNS server.
   Hardware devices may be of such limited resources that DNS SRV access
   is inappropriate.  Firewalls and other restrictive routing mechanisms
   may need to be dealt with before a reliable syslog connection can be
   established.  In these cases, DNS might not be the most appropriate
   configuration mechanism.








































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3. The RAW Profile

3.1 RAW Profile Overview

   The RAW profile is designed for minimal implementation effort, high
   efficiency, and backwards compatibility.  It is appropriate
   especially in cases where legacy syslog processing will be applied.

   It should be noted that even though the RAW profile uses the same
   format for message payloads as the UDP version of syslog uses,
   delivery is reliable.  The RAW syslog profile is a profile of BEEP
   [3], and BEEP guarantees ordered reliable delivery of messages within
   each individual channel.

   When the profile is started, no piggyback data is supplied.  All BEEP
   messages in the RAW profile are specified as having a MIME Content-
   Type [6] of application/octet-stream.  Once the channel is open, the
   listener (not the initiator) sends a MSG message indicating it is
   ready to act as a syslog sink.  (Refer to [3]'s Section 2.1 for a
   discussion of roles that a BEEP peer may perform, including
   definitions of the terms "listener", "initiator", "client", and
   "server".)

   The initiator uses ANS replies to supply one or more syslog entries
   in the current UDP format, as specified in [1]'s Section 3.  When the
   initiator has no more entries to send, it finishes with a NUL reply
   and closes the channel.

   An example might appear as follows:

      L: <wait for incoming connection>
      I: <establish connection>
      L: RPY 0 0 . 0 201
      L: Content-type: application/beep+xml
      L:
      L: <greeting>
      L:   <profile
      L:     uri='http://xml.resource.org/profiles/syslog/COOKED' />
      L:   <profile uri='http://xml.resource.org/profiles/syslog/RAW' />
      L: </greeting>
      L: END
      I: RPY 0 0 . 0 52
      I: Content-type: application/beep+xml
      I:
      I: <greeting />
      I: END
      I: MSG 0 1 . 52 133
      I: Content-type: application/beep+xml



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      I:
      I: <start number='1'>
      I:   <profile uri='http://xml.resource.org/profiles/syslog/RAW' />
      I: </start>
      I: END
      L: RPY 0 1 . 201 100
      L: Content-type: application/beep+xml
      L:
      L: <profile uri='http://xml.resource.org/profiles/syslog/RAW' />
      L: END
      L: MSG 1 0 . 0 50
      L:
      L: Central Services. This has not been a recording.
      L: END
      I: ANS 1 0 . 0 61 0
      I:
      I: <29>Oct 27 13:21:08 ductwork imxpd[141]: Heating emergency.END
      I: ANS 1 0 . 61 58 1
      I:
      I: <29>Oct 27 13:22:15 ductwork imxpd[141]: Contact Tuttle.END
      I: NUL 1 0 . 119 0
      I: END
      L: MSG 0 3 . 301 70
      L: Content-Type: application/beep+xml
      L:
      L: <close number='1' code='200' />
      L: END
      I: RPY 0 3 . 185 46
      I: Content-Type: application/beep+xml
      I:
      I: <ok />
      I: END
      I: MSG 0 4 . 231 72
      I: Content-Type: application/beep+xml
      I:
      I: <close number='0' code='200' />
      I: END
      L: RPY 0 4 . 371 46
      L: Content-type: application/beep+xml
      L:
      L: <ok />
      L: END
      L: <closes connection>
      I: <closes connection>
      L: <awaits next connection>






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   Here we see a BEEP session established, followed by the use of the
   RAW profile.  The initiator is a device, while the listener is a
   collector.  The initiator opens the channel, but the listener sends
   the first MSG.  This allows the initiator to send any number of ANS
   replies carrying syslog event messages.  The initiator sends a NUL
   reply to indicate it is finished.  Upon receiving the NUL, the
   listener closes the RAW channel.  The initiator has the choice of
   closing the entire BEEP session or opening a new syslog channel (RAW
   or COOKED) for more transfers.  In this example, the initiator
   chooses to close the entire BEEP session.

   The overhead for one ANS frame is about thirty octets, once the
   initial handshakes have been exchanged.  If this overhead is too
   high, then messages are likely being generated at a high rate.  In
   this case, multiple syslog messages can be aggregated into a single
   ANS frame, each separated by a CRLF sequence from the preceding.  The
   final message still MUST NOT end with a CRLF.

   For example,

      L: MSG 1 0 . 0 50
      L:
      L: Central Services. This has not been a recording.
      L: END
      I: ANS 1 0 . 0 119 0
      I:
      I: <29>Oct 27 13:21:08 ductwork imxpd[141]: Heating emergency.
      I: <29>Oct 27 13:21:09 ductwork imxpd[141]: Contact Tuttle.END
      I: NUL 1 0 . 119 0
      I: END

3.2 RAW Profile Identification and Initialization

   The RAW syslog profile is identified as

           http://xml.resource.org/profiles/syslog/RAW

   in the BEEP "profile" element during channel creation.

   No data is piggybacked during channel creation.











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3.3 RAW Profile Message Syntax

   All BEEP messages in this profile have a MIME content-type of
   application/octet-stream.  The listener's first BEEP message is
   ignored and indeed may be empty except for headers; hence, any syntax
   is acceptable.

   The ANS replies the initiator sends in response MUST be formatted
   according to Section 4 of [1].  In particular, If the receiver is
   acting as a relay, then it MUST follow the rules as laid out in
   Section 4.2.2 of [1].

   If multiple syslog messages are included in a single ANS reply, each
   is separated from the preceding with a CRLF.  There is no ending
   delimiter, but each syslog event message body length MUST be 1024
   bytes or less, excluding BEEP framing overhead.  Note that there MUST
   NOT be a CRLF between the text of the final syslog event message and
   the "END" marking the trailer of the BEEP frame.

3.4 RAW Profile Message Semantics

   The listener's opening BEEP MSG message has no semantics.  (It is a
   good place to put in an identifying greeting.) The initiator's ANS
   replies MUST specify a facility, severity, and textual message, as
   described in [1].


























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4. The COOKED Profile

4.1 COOKED Profile Overview

   The COOKED profile is designed for new implementations of syslog
   protocol handlers.  It provides a much finer grain of information
   tagging, allowing a better degree of automation in processing.
   Naturally, it includes more overhead as well in support of this.

   The COOKED profile supports three elements of interest:

   o  The "iam" element identifies the sender to the receiver, allowing
      each peer to name itself for the other, and specifying the roles
      (device, relay, or collector) each is taking on.

   o  The "entry" element provides a parsed version of the syslog entry,
      with the various fields of interest broken out.

   o  The "path" element identifies a list of relays through which a
      tagged collection of "entry" elements has passed, along with a set
      of flags indicating what assurances of security have been in
      effect throughout its delivery.

4.2 COOKED Profile Identification and Initialization

   The COOKED syslog profile is identified as

       http://xml.resource.org/profiles/syslog/COOKED

   in the BEEP "profile" element during channel creation.

   During channel creation, the corresponding "profile" element in the
   BEEP "start" element may contain an "iam" element.  If channel
   creation is successful, then before sending the corresponding reply,
   the BEEP peer processes the "iam" element and includes the resulting
   response in the reply.  This response will be an "ok" element or an
   "error" element.  The choice of which element is returned is
   dependent on local provisioning of the recipient.  Including an "iam"
   in the initial "start" element has exactly the same semantics as
   passing it as the first MSG message on the channel.

4.3 COOKED Profile Message Syntax

   All BEEP messages in this profile have a MIME Content-Type [6] of
   application/beep+xml.  The syntax of the individual elements is
   specified in Section 7.





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4.4 COOKED Profile Message Semantics

   Initiators issue two elements: "iam" and "entry", each using a "MSG"
   message.  The listener issues "ok" in "RPY" messages and "error" in
   "ERR" messages.  (See [3]'s Section 2.3.1 for the definitions of the
   "error" and "ok" elements.)

4.4.1 The IAM Element

   The "iam" element serves to identify a device, relay, or collector at
   one end of the BEEP channel to the device, relay, or collector at the
   other end of the channel.  The "iam" element includes the type of
   peer (device, relay, or collector), the fully qualified domain name
   of the peer, and an IP address of the peer.  (The IP address chosen
   SHOULD be the IP address associated with the underlying transport
   protocol carrying the channel.)  The character data of the element is
   free-form human-readable text.  It may be used to further identify
   the peer, such as by describing the physical location of the machine.

   An "iam" element may be sent by the initiator of the channel at any
   time.  The listener responds to an "iam" element with an "ok"
   (indicating acceptance), or an "error" (indicating rejection).  The
   identity and role in effect is specified by the most recent "iam"
   answered with an "ok".

   An "iam" could be rejected (with an "error" element) by the listener
   if the privacy or authentication that has been negotiated is
   inadequate or if the authenticated user does not have authorization
   to serve in the specified role.  It is expected that most
   installations will require an "iam" from the peer before accepting
   any "entry" messages.




















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   For example, a successful creation might look like this:

      I: MSG 0 10 . 1832 259
      I: Content-type: application/beep+xml
      I:
      I: <start number='1'>
      I:   <profile
      I:       uri='http://xml.resource.org/profiles/syslog/COOKED'>
      I:     <![CDATA[ <iam fqdn='lowry.example.com' ip='10.0.0.27'
      I:       type='device'/> ]]>
      I:   </profile>
      I: </start>
      L: END
      L: RPY 0 10 . 704 138
      L: Content-type: application/beep+xml
      L:
      L: <profile uri='http://xml.resource.org/profiles/syslog/COOKED'>
      L:   <![CDATA[ <ok /> ]]>
      L: </profile>
      L: END

   A creation with an embedded "iam" that fails might look like this:

      C: MSG 0 12 . 1832 259
      C: Content-type: application/beep+xml
      C:
      C: <start number='1'>
      C:   <profile
      C:       uri='http://xml.resource.org/profiles/syslog/COOKED'>
      C:     <![CDATA[ <iam fqdn='tuttle.example.com' ip='10.0.0.29'
      C:       type='relay'/> ]]>
      C:   </profile>
      C: </start>
      C: END
      S: RPY 0 12 . 704 241
      S: Content-type: application/beep+xml
      S:
      S: <profile uri='http://xml.resource.org/profiles/syslog/COOKED'>
      S:   <![CDATA[
      S:     <error code='535'>User 'buttle.example.com' not allowed
      S:       to "iam" for 'tuttle.example.com'</error> ]]>
      S: </profile>
      S: END

   In this case, the error code indicates that the user
   "buttle.example.com" has logged in via some SASL profile, but the
   syslog COOKED profile implementation is claiming to be
   "tuttle.example.com", a mismatch that the server is disallowing.



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4.4.2 The ENTRY Element

   The "entry" element carries the details of a single syslog entry. The
   attributes of an "entry" element include "facility", "severity",
   "timestamp", "hostname", and "tag".  "Facility" and "severity" have
   the semantics defined in [1]'s 4.1.  The other attributes have the
   semantics as in Sections 4.2.1 and 4.2.3 of [1].  An "entry" element
   can also contain a "pathID" attribute, described below.

   If the client is a relay, the "entry" SHOULD also contain the
   attributes "deviceFQDN" and "deviceIP", specifying the FQDN and IP
   address of the device that originally created the entry.  These
   attributes may be added by either the relay or the originating
   device.  If possible, the device SHOULD add these entries, referring
   to the interface most closely associated with the syslog entry.
   Before a relay forwards an entry from a device that does not carry
   these attributes, it SHOULD add them based on the "iam" element it
   has received from the device, or based on the underlying transport
   connection address.  A relay MUST NOT add these fields if they are
   missing and an "iam" element on the channel has indicated that
   messages are coming from another relay.

   The "pathID" attribute indicates the path over which this entry has
   travelled, from device through relays to the final collector.
   Syntactically, its value is a string of digits that must match the
   "pathID" attribute of a "path" element sent earlier over the current
   channel.  Semantically, it indicates that the list of relays and
   flags indicated in that earlier "path" element apply to this "entry"
   element.

   The character data for the element is the unstructured syslog event
   message being logged.  If the original device delivers the message
   for the first time via the COOKED profile, it may have any structure
   inside the CDATA.  However, for maximum compatibility, the device
   SHOULD format the CDATA of the message in accordance with Sections
   4.2.1 through 4.2.3 of [1].















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   In the message is being relayed, "tag" SHOULD be those of the
   original device generating the entry (unless the device cannot supply
   a tag).  The "timestamp" SHOULD be that of the original entry
   generation time, rather than the time the entry was passed outward
   from the relay.  The "hostname" SHOULD be the host name or IP address
   by which the device knows itself; this MUST follow the rules
   established in Sections 4.2.1 through 4.2.3 of [1].  The original
   contents of the syslog message MUST be preserved in the CDATA of the
   "entry" element; this includes preservation of exact content during
   translation from the UDP or RAW formats.  In particular, the
   timestamps MUST NOT be rewritten in the CDATA of the "entry" element,
   the tag MUST NOT be removed from the CDATA even if presented in the
   "entry" attributes as well, and so on.

   To be consistent with the spirit of [1], a relay receiving a message
   that does not contain a valid priority, timestamp or hostname will
   follow the same general rules as described in section 4.2.2 of [1]
   while including the exact contents of the received syslog packet as
   the CDATA.  The values of the facility and severity will be construed
   to be 8 and 6 respectively and will be placed into the appropriate
   attributes of the "entry" element.  The hostname will be the name of
   the device as it is known to the relay and will also be inserted into
   the "entry" element's attributes.  The timestamp would be set to the
   received time, inserted only into the attributes of the "entry"
   element.  As an example, consider this message received on UDP port
   514 and interpreted as a traditional syslog message, assuming the
   underlying IP source address is that of the "pipeworks" machine:

     <.....eeeek!

   To be relayed, it must be modified as follows:

         C: MSG 1 0 . 2079 156
         C: Content-Type: application/beep+xml
         C:
         C: <entry facility='8' severity='6'
         C:   hostname='pipeworks'
         C:   timestamp='Oct 31 23:59:59'
         C:  >&lt;.....eeeek!</entry>
         C: END
         S: RPY 1 0 . 933 45
         S: Content-Type: application/beep+xml
         S:
         S: <ok/>
         S: END






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   As another example, consider a message being received that does not
   properly adhere to the conventions described in Section 4.2.2 of [1].
   In particular, the timestamp has a year, making it a nonstandard
   format:

        <166> 1990 Oct 22 01:00:00 bomb tick[0]: BOOM!

   This would be relayed as follows:

         C: MSG 1 0 . 2235 242
         C: Content-Type: application/beep+xml
         C:
         C: <entry facility='160' severity='6'
         C:   hostname='bomb'
         C:   deviceFQDN='bomb.terrorist.net' deviceIP='10.0.0.83'
         C:   timestamp='Oct 22 01:00:04'
         C:  >&lt;166> 1990 Oct 22 01:00:00 bomb tick[0]: BOOM!</entry>
         C: END
         S: RPY 1 0 . 978 45
         S: Content-Type: application/beep+xml
         S:
         S: <ok/>
         S: END

   Note that the tag value was not readily apparent from the received
   message (due to the failed parsing of the timestamp), so it was not
   included in the "entry" element.

   It is explicitly permitted for a relay to parse raw messages in a
   more sophisticated way, but all implementations MUST be able to parse
   messages presented in the format described in [1].  A more
   sophisticated relay could have recognized the year and completely
   parsed out the correct time, tag, and hostname, but such additional
   parsing capability is OPTIONAL.

   Consider the following example, in contrast:

        <166> Oct 22 01:00:00 bomb tick[0]: BOOM!













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   This conformant message would be relayed as follows:

         C: MSG 1 0 . 2477 248
         C: Content-Type: application/beep+xml
         C:
         C: <entry facility='160' severity='6'
         C:   hostname='bomb'
         C:   deviceFQDN='bomb.terrorist.net' deviceIP='10.0.0.83'
         C:   timestamp='Oct 22 01:00:00' tag='tick'
         C:  >&lt;166> Oct 22 01:00:00 bomb tick[0]: BOOM!</entry>
         C: END
         S: RPY 1 0 . 1023 45
         S: Content-Type: application/beep+xml
         S:
         S: <ok/>
         S: END

   In this case, the tag is detected and the timestamp represents the
   message generation time rather than the message reception time.

   Finally, the "entry" element may also contain an "xml:lang"
   attribute, indicating the language in which the CDATA content of the
   tag is presented, as described in [7].

   The "entry" element is answered with either an empty "ok" element if
   everything was successful, or a standard "error" element if there was
   a problem.  An "entry" element can be rejected if no "iam" element
   has been accepted by the listener.  It can also be rejected if the
   user authenticated on the BEEP session (if any) does not have the
   authority to generate (as a device) or relay that entry.  An error is
   also possible if the "pathID" attribute refers to an unknown (or
   rejected) "path" element.



















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   A successful exchange of an "entry" element may look like this:

      C: MSG 1 0 . 2725 173
      C: Content-Type: application/beep+xml
      C:
      C: <entry facility='24' severity='5'
      C:   timestamp='Jan 26 15:16:17'
      C:   hostname='pipework' tag='imxp'>
      C:     No 27B/6 available</entry>
      C: END
      S: RPY 1 0 . 1068 45
      S: Content-Type: application/beep+xml
      S:
      S: <ok/>
      S: END

   Here, the device IP address and FQDN are taken from the "iam"
   element, if any, or from the underlying connection information.

   An example where an "entry" element is rejected with an "error"
   element:

      C: MSG 1 2 . 2898 223
      C: Content-Type: application/beep+xml
      C:
      C: <entry facility='24' severity='5' timestamp='Jan 02 13:22:15'
      C:   deviceFQDN='jack.example.net' deviceIP='10.0.0.83'
      C:   tag='imxpd'>
      C:     Replacement device found in nostril.
      C: </entry>
      C: END
      S: ERR 1 2 . 1113 111
      S: Content-Type: application/beep+xml
      S:
      S: <error code='554'>Not allowed to relay for
      S:    jack.example.net</error>
      S: END

   Here, the client attempts to relay an entry on behalf of
   jack.example.com, but the entry is refused by the collector for
   administrative reasons.  This may occur, for example, if
   lowry.example.com is in a different department than jack.example.com.









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4.4.3 The PATH Element

   The "path" element serves to describe a list of the relays through
   which that element has passed, along with a set of flags that
   indicate the properties that all links from the device to the relay
   have shared in common.  Each "path" element contains either another
   "path" element or is empty.  An empty "path" element identifies a
   device, while a "path" element with a nested "path" element
   identifies a relay.  Each "path" element names a FQDN and IP address
   of the interface that sent the element.  Each "path" element also
   names a FQDN and IP address for the interface that received the
   element.  Each "path" element also carries a "linkprops" attribute,
   specifying the properties of the link it describes.

   Each "path" element has a "pathID" attribute which must be unique for
   all "path" elements sent on this channel since its inception.
   Syntactically, the "pathID" attribute is a string of digits.
   Semantically, it serves to identify one "path" element out of many,
   and it serves to link a "path" element with one or more "entry"
   elements.  Any "pathID" attribute is unrelated to any "pathID"
   attribute in nested "path" elements or on other channels.

   Each "path" element has a "fromFQDN" attribute and an "fromIP"
   attribute.  The "fromFQDN" attribute SHOULD be the fully qualified
   domain name of the interface over which the "path" element was sent.
   (The "fromFQDN" can be omitted if that interface has no DNS entry.)
   Similarly, the "fromIP" attribute MUST be the IP address of the
   interface over which the "path" element was sent.

   Each "path" element has a "toFQDN" attribute and an "toIP" attribute.
   The "toFQDN" attribute SHOULD be the fully qualified domain name of
   the interface over which the "path" element was received.  (The
   "toFQDN" can be omitted if that interface has no DNS entry.)
   Similarly, the "toIP" attribute MUST be the IP address of the
   interface over which the "path" element was received.

   Finally, each "path" element carries a "linkprops" attribute.  This
   is syntactically a string of individual characters, each indicating
   one property of the channel over which this "path" element is being
   carried.  Note that outer "path" elements may have stronger
   guarantees than inner "path" elements; care should be taken in the
   interpretation of flags.  The semantics of each possible character in
   this string are as follows:








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   o: When present, "o" (lower-case letter "o") indicates that weak
      privacy has been negotiated over this link, weakly protecting from
      observation the content of entries associated with this "path"
      element.  (Weak privacy is encryption with less than 80 bits of
      key.)

   O: When present, "O" (upper-case letter "O") indicates that strong
      privacy has been negotiated over this link, strongly protecting
      from observation the content of entries associated with this
      "path" element.  (Strong privacy is encryption with 80 bits or
      more of key, or a transfer mechanism that is otherwise impossible
      to eavesdrop upon.)

   U: When present, "U" indicates that a valid user has been
      authenticated (via SASL or TLS) and an "iam" element has been
      accepted.

   A: When present, "A" indicates that this link has been protected by
      an authentication layer, authenticating the source of every
      "entry" associated with this path.

   R: When present, "R" indicates that this link has been protected
      against message replay.

   I: When present, "I" indicates that this link has been protected
      against modifications of messages in passing.  ("I" stands for
      message Integrity.)

   L: When present, "L" indicates that this link has been protected
      against loss of messages.  That is, this is a reliable delivery
      link.

   D: When present, "D" indicates that the "from" side of this link is a
      device.  If this is not present on the innermost "path" element,
      "entry" elements associated with this path have not been carried
      by the COOKED profile for their entire lifetime.

   Upon receiving a "path" element, the peer MUST perform the following
   checks:

   o  The "fromFQDN" and "fromIP" must match the underlying transport
      connection.

   o  The flags in the "linkprops" attribute must match the attributes
      of the session.

   o  The "toFQDN" and "toIP" must match the underlying transport
      connection.



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   o  The "pathID" attribute must be unique with respect to all other
      "path" elements received on this channel.

   If all these checks pass, the "path" element is accepted with an "ok"
   element.  Otherwise, an "error" element is generated with an
   appropriate code.  In addition, if any of the nested "path" elements
   refer to the machine receiving the element, it may indicate a routing
   loop in the configuration for the so-identified path, and appropriate
   measures should be taken.

   If the peer receiving an "entry" element is receiving it directly
   from a device via either syslog-conn profile, and the device has not
   generated a "path" element, the receiver may itself generate an
   appropriate "path" element, either to be recorded in the logs (if
   this peer is a collector) or passed to the next peer (if this peer is
   a relay).  If a peer receives a syslog message via UDP, it may
   optionally generate an appropriate "peer" element based on any
   cryptographic information provided in the message itself.

   When a peer receives a "path" element, it remembers it for future
   use.  A collector will store it in the log for later reference.  A
   relay will remember it.  When an "entry" arrives referencing the
   received "path" element, and that entry needs to be forwarded to
   another relay or collector, and no appropriate "path" element has
   already been generated, an appropriate "path" element is generated
   and sent over the outbound channel before the entry is forwarded.  An
   appropriate "path" element is created by taking the received "path"
   element, wrapping it in a new "path" element with the appropriate
   attributes, and assigning it a new "pathID" attribute.  When future
   "entry" elements arrive with the same incoming "pathID" attribute,
   and they need to be forwarded to a channel over which an appropriate
   "pathID" attribute has already been sent, only the "pathID" attribute
   of the "entry" element needs to be rewritten to refer to the "path"
   element on the outgoing channel.

   It should be noted that the majority of the complexity in managing
   "path" elements arises only in relays.  In particular, devices never
   need to generate "path" elements and collectors need only verify
   them, log them, and possibly use them in displays and reports.
   Collectors do not need to generate "path" elements or rewrite "entry"
   elements.  Hence, only in complex configurations (where they are most
   useful) do complex "path" configurations occur.









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   For example, here is a path element sent from
   lowry.records.example.com to kurtzman.records.example.com.  It
   indicates that entries from lowry to kurtzman tagged with
   pathID='173' originated from screen.lowry.records.example.com.  It
   indicates that screen.lowry.records.example.com is believed by
   lowry.records.example.com to be the originating device, and that
   entries over this path are delivered without loss and without
   modification, although messages might be replayed or observed.  The
   link between lowry and kurtzman, however, avoids replay attacks, lost
   messages, and modifications to messages.  While
   screen.lowry.records.example.com has not authenticated itself to
   lowry.records.example.com, lowry claims to have authenticated itself
   to kurtzman.

      C: MSG 2 1 . 3121 426
      C: Content-type: application/beep+xml
      C:
      C: <path fromFQDN='lowry.records.example.com'
      C:       fromIP='10.0.0.50'
      C:       toFQDN='kurtzman.records.example.com'
      C:       toIP='10.0.0.51'
      C:       linkprops='ULRI'
      C:       pathID='173'>
      C: <path fromFQDN='screen.lowry.records.example.com'
      C:       fromIP='10.0.0.47'
      C:       toFQDN='lowry.records.example.com'
      C:       toIP='10.0.0.50'
      C:       linkprops='DLI'
      C:       pathID='24'>
      C: </path>
      C: </path>
      C: END
      S: ERR 2 1 . 1224 114
      S: Content-type: application/beep+xml
      S:
      S: <error code='530'>linkprops includes 'U'
      S:   but no 'iam' received</error>
      S: END

   However, kurtzman.records.example.com rejects the "path" element,
   since the "linkprops" attribute claims that lowry has authenticated
   itself, but kurtzman disagrees, not having received an "iam" element.









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   In a second example, this "path" element informs
   collector.example.com that the records department's firewall will be
   forwarding "entry" elements with a "pathID" attribute whose value is
   "17".  These "entry" elements will be coming in on the "10.0.0.2"
   interface of the firewall, to be forwarded out the "134.130.74.56"
   interface of the firewall.  The final hop has all possible
   guarantees, although the entries transferred within the records
   department (behind the firewall) may have been observed in passing.

      C: MSG 2 2 . 3547 813
      C: Content-type: application/beep+xml
      C:
      C: <path fromFQDN='fwall.records.example.com'
      C:       fromIP='134.130.74.56'
      C:       toFQDN='collector.example.com'
      C:       toIP='134.130.74.12'
      C:       linkprops='OUARIL'
      C:       pathID='17'>
      C: <path fromFQDN='kurtzman.records.example.com'
      C:       fromIP='10.0.0.50'
      C:       toFQDN='fwall.records.example.com'
      C:       toIP='10.0.0.2'
      C:       linkprops='ULRI'
      C:       pathID='120'>
      C: <path fromFQDN='lowry.records.example.com'
      C:       fromIP='10.0.0.50'
      C:       toFQDN='kurtzman.records.example.com'
      C:       toIP='10.0.0.51'
      C:       linkprops='ULRI'
      C:       pathID='173'>
      C: <path fromFQDN='screen.lowry.records.example.com'
      C:       fromIP='10.0.0.47'
      C:       toFQDN='lowry.records.example.com'
      C:       toIP='10.0.0.50'
      C:       linkprops='DLI'
      C:       pathID='24'>
      C: </path></path></path></path>
      C: END
      S: RPY 2 2 . 1338 45
      S: Content-type: application/beep+xml
      S:
      S: <ok/>
      S: END








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   As a final example, an "entry" element from Lowry's screen arrives at
   the firewall.  The "path" attribute is rewritten, and it is forwarded
   on to the collector.

      The entry arrives on the 10.0.0.2 interface:

      C: MSG 2 3 . 4360 250
      C: Content-Type: application/beep+xml
      C:
      C: <entry facility='24' severity='5'
      C:   timestamp='Oct 27 13:24:12'
      C:   deviceFQDN='screen.lowry.records.example.com'
      C:   deviceIP='10.0.0.47'
      C:   pathID='173'
      C:   tag='dvd'>
      C:     Job paused - Boss watching.
      C: </entry>
      C: END
      S: RPY 2 3 . 1383 45
      S: Content-Type: application/beep+xml
      S:
      S: <ok/>
      S: END

      It is forwarded out the 134.130.74.56 interface:

      C: MSG 7 9 . 9375 276
      C: Content-Type: application/beep+xml
      C:
      C: <entry facility='24' severity='5'
      C:   timestamp='Oct 27 13:24:12'
      C:   deviceFQDN='screen.lowry.records.example.com'
      C:   deviceIP='10.0.0.47'
      C:   pathID='17'
      C:   tag='dvd'>
      C:     Job paused - Boss watching.
      C: </entry>
      C: END
      S: RPY 7 9 . 338 45
      S: Content-Type: application/beep+xml
      S:
      S: <ok/>
      S: END

   A discussion of the wisdom of configuring Lowry's machine to forward
   such messages via Kurtzman's machine is beyond the scope of this
   document.




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5. Additional Provisioning

   In more advanced configurations, syslog devices, relays, and
   collectors can be configured to support various delivery priorities.
   Multiple channels running the same profile can be opened between two
   peers, with higher priority syslog messages routed to a channel that
   is given more bandwidth.  Such provisioning is a local matter.

   syslog [1] discusses a number of reasons why privacy and
   authentication of syslog entry messages may be important in a
   networked computing environment.  The nature of BEEP allows for
   convenient layering of authentication and privacy over any BEEP
   channel.

5.1 Message Authenticity

   Section 6.2 of [1] discusses the dangers of unauthenticated syslog
   entries.  To prevent inauthentic syslog event messages from being
   accepted, configure syslog peers to require the use of a strong
   authentication technology for the BEEP session.

   If provisioned for message authentication, implementations SHOULD use
   SASL mechanism DIGEST-MD5 [8] to provision this service.

5.2 Message Replay

   Section 6.3.4 of [1] discusses the dangers of syslog message replay.
   To prevent syslog event messages from being replayed, configure
   syslog peers to require the use of a strong authentication technology
   for the BEEP session.

   If provisioned to detect message replay, implementations SHOULD use
   SASL mechanism DIGEST-MD5 [8] to provision this service.

5.3 Message Integrity

   Section 6.5 of [1] discusses the dangers of syslog event messages
   being maliciously altered by an attacker.  To prevent messages from
   being altered, configure syslog peers to require the use of a strong
   authentication technology for the BEEP session.

   If provisioned to protect message integrity, implementations SHOULD
   use SASL mechanism DIGEST-MD5 [8] to provision this service.








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5.4 Message Observation

   Section 6.6 of [1] discusses the dangers (and benefits) of syslog
   messages being visible at intermediate points along the transmission
   path between device and collector.  To prevent messages from being
   viewed by an attacker, configure syslog peers to require the use of a
   transport security profile for the BEEP session.  (However, other
   traffic characteristics, e.g., volume and timing of transmissions,
   remain observable.)

   If provisioned to secure messages against unauthorized observation,
   implementations SHOULD use the TLS profile [3] to provision this
   service.  The cipher algorithm used SHOULD be
   TLS_RSA_WITH_3DES_EDE_CBC_SHA.

5.5 Summary of Recommended Practices

   For the indicated protections, implementations SHOULD be configured
   to use the indicated mechanisms:

    Desired Protection  SHOULD tune using
    ------------------  -----------------
    Authentication      http://iana.org/beep/SASL/DIGEST-MD5
      + Replay          http://iana.org/beep/SASL/DIGEST-MD5
        + Integrity     http://iana.org/beep/SASL/DIGEST-MD5
          + Observation http://iana.org/beep/TLS

   BEEP peer identities used for authentication SHOULD correspond to the
   FQDN of the initiating peer.  That is, a relay running on
   relay.example.com should use a "user ID" of "relay.example.com"
   within the SASL authentication profiles, as well as in the FQDN of
   the "iam" element.



















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6. Initial Registrations

6.1 Registration: The RAW Profile

   Profile Identification: http://xml.resource.org/profiles/syslog/RAW

   Messages exchanged during Channel Creation: None

   Messages starting one-to-one exchanges: Anything

   Messages in positive replies: None

   Messages in negative replies: None

   Messages in one-to-many exchanges: Anything

   Message Syntax: See Section 3.3

   Message Semantics: See Section 3.4

   Contact Information: See the "Authors' Addresses" section of this
      memo

6.2 Registration: The COOKED Profile

   Profile Identification:
      http://xml.resource.org/profiles/syslog/COOKED

   Messages exchanged during Channel Creation: iam

   Messages starting one-to-one exchanges: iam, entry, path

   Messages in positive replies: ok

   Messages in negative replies: error

   Messages in one-to-many exchanges: None

   Message Syntax: See Section 4.3

   Message Semantics: See Section 4.4

   Contact Information: See the "Authors' Addresses" section of this
      memo







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7. The syslog DTD

   The following is the DTD defining the valid elements for the syslog
   over BEEP mapping.

   <!--
     DTD for syslog over BEEP, as of 2000-10-10

     Refer to this DTD as:

       <!ENTITY % SYSLOG PUBLIC "-//Blocks//DTD SYSLOGRELIABLE//EN" "">
       %SYSLOG;
     -->

   <!--
     Contents

       Overview

       Includes
       Profile Summaries
       Entity Definitions

       Operations
           iam
           entry
           path
     -->

   <!--
     Overview

       Syslog packets delivered via BEEP

     -->

   <!-- Includes -->

          <!ENTITY % BEEP PUBLIC "-//Blocks//DTD BEEP//EN"
                     "">
          %BEEP;










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   <!--
     Profile summaries

       BEEP profile SYSLOG-RAW

       role        MSG        ANS        ERR
       ====        ===        ===        ===
        L          text       text       text

       BEEP profile SYSLOG-COOKED

       role        MSG        RPY        ERR
       ====        ===        ===        ===
       I or L      iam        ok         error
       I or L      entry      ok         error
       I or L      path       ok         error

   -->

   <!--
     Entity Definitions

           entity        syntax/reference     example
           ======        ================     =======
       a fully qualified domain name
           FQDN          See [RFC-1034]       www.example.com

       a dotted-quad IP address
           IP            1*3DIGIT "." 1*3DIGIT "."
                          1*3DIGIT "." 1*3DIGIT
                                              10.0.0.27
       a syslog facility
           FACILITY      See [1]
                         1*3DIGIT             80

       a syslog severity
           SEVERITY      See [1]
                         DIGIT                 4

       a timestamp       See [1]               Jan 03 18:43:12
           TIMESTAMP

       an identifying integer
           IDINT         1*DIGIT               1027

   -->





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   <!ENTITY % FQDN         "CDATA">
   <!ENTITY % IP           "CDATA">
   <!ENTITY % FACILITY     "CDATA">
   <!ENTITY % SEVERITY     "CDATA">
   <!ENTITY % TIMESTAMP    "CDATA">
   <!ENTITY % IDINT        "CDATA">


   <!--
     The iam element declares the role and identity of the peer
     issuing it. The contents of the element may include human-readable
     informative text, such as the physical location of the computer
     issuing the "iam".

     -->

   <!ELEMENT iam         (#PCDATA)>
   <!ATTLIST iam
             fqdn        %FQDN;                   #REQUIRED
             ip          %IP;                     #REQUIRED
             type        (device|relay|collector) #REQUIRED>

   <!--
     The entry element conveys a single syslog message.
     -->

   <!ELEMENT entry       (#PCDATA)>
   <!ATTLIST entry
             xml:lang    %LANG;                   "i-default"
             facility    %FACILITY;                #REQUIRED
             severity    %SEVERITY;                #REQUIRED
             timestamp   %TIMESTAMP;               #IMPLIED
             tag         %ATEXT;                   #IMPLIED
             deviceFQDN  %FQDN;                    #IMPLIED
             deviceIP    %IP;                      #IMPLIED
             pathID      %IDINT;                   #IMPLIED>















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   <!--
     The path element conveys a list of relays through which
     entries have passed.
     -->

   <!ELEMENT path        (path?)>
   <!ATTLIST path
             pathID      %IDINT;                   #REQUIRED
             fromFQDN    %FQDN;                    #IMPLIED
             fromIP      %IP;                      #REQUIRED
             toFQDN      %FQDN;                    #IMPLIED
             toIP        %IP;                      #REQUIRED
             linkprops   %ATEXT;                   #REQUIRED>

   <!-- End of DTD -->




































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8. Reply Codes

   The following error codes are used in the protocol:

   code    meaning
   ====    =======
   200     success

   421     service not available

   451     requested action aborted
           (e.g., local error in processing)

   454     temporary authentication failure

   500     general syntax error
           (e.g., poorly-formed XML)

   501     syntax error in parameters
           (e.g., non-valid XML)

   504     parameter not implemented

   530     authentication required

   534     authentication mechanism insufficient
           (e.g., too weak, sequence exhausted, etc.)

   535     authentication failure

   537     action not authorized for user

   538     authentication mechanism requires encryption

   550     requested action not taken
           (e.g., no requested profiles are acceptable)

   553     parameter invalid

   554     transaction failed
           (e.g., policy violation)










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9. IANA Considerations

9.1 Registration: BEEP Profiles

   The IANA registers the profiles specified in Section 6, and selects
   IANA-specific URIs "http://iana.org/beep/SYSLOG/RAW" and
   "http://iana.org/beep/SYSLOG/COOKED".

9.2 Registration: The System (Well-Known) TCP port number for syslog-
    conn

   A single well-known port (601) is allocated to syslog-conn.  In-band
   negotiation determines whether COOKED or RAW syslog-conn is in use.

   Protocol Number: TCP

   Message Formats, Types, Opcodes, and Sequences: See Section 3.3 and
      Section 4.4.

   Functions: See Section 3.4 and Section 4.4.

   Use of Broadcast/Multicast: none

   Proposed Name: Reliable syslog service

   Short name: syslog-conn

   Contact Information: See the "Authors' Addresses" section of this
      memo






















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10. Security Considerations

   Consult Section 6 of [1] for a discussion of security issues for the
   syslog service.  In addition, since the RAW and COOKED profiles are
   defined using the BEEP framework, consult [3]'s Section 8 for a
   discussion of BEEP-specific security issues.

   BEEP is used to provide communication security but not object
   integrity.  In other words, the messages "on the wire" can be
   protected, but a compromised device may undetectably generate
   incorrect messages, and relays and collectors can modify, insert, or
   delete messages undetectably.  Other techniques must be used to
   assure that such compromises are detectable.

11. Acknowledgements

   The authors gratefully acknowledge the contributions of Christopher
   Calabrese, Keith McCloghrie, Balazs Scheidler, and David Waitzman.

12. References

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

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

   [3]  Rose, M., "The Blocks Extensible Exchange Protocol Core", RFC
        3080, March 2001.

   [4]  Rose, M., "Mapping the BEEP Core onto TCP", RFC 3081, March
        2001.

   [5]  Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
        specifying the location of services (DNS SRV)", RFC 2782,
        February 2000.

   [6]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part Two: Media Types", RFC 2046, November
        1996.

   [7]  Alvestrand, H., "Tags for the Identification of Languages", BCP
        47, RFC 3066, January 2001.

   [8]  Leach, P. and C. Newman, "Using Digest Authentication as a SASL
        Mechanism", RFC 2831, May 2000.






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Authors' Addresses

   Darren New
   5390 Caminito Exquisito
   San Diego, CA  92130
   US

   Phone: +1 858 350 9733
   EMail: dnew@san.rr.com


   Marshall T. Rose
   Dover Beach Consulting, Inc.
   POB 255268
   Sacramento, CA  95865-5268
   US

   Phone: +1 916 483 8878
   EMail: mrose@dbc.mtview.ca.us
































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Acknowledgement

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