syslog Working Group R. Gerhards
Internet-Draft Adiscon GmbH
Intended status: Standards Track November 29, 2006
Expires: June 2, 2007
The syslog Protocol
draft-ietf-syslog-protocol-19.txt
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Copyright (C) The Internet Society (2006).
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Abstract
This document describes the syslog protocol, which is used to convey
event notification messages. This protocol utilizes a layered
architecture, which allows the use of any number of transport
protocols for transmission of syslog messages. It also provides a
message format that allows vendor-specific extensions to be provided
in a structured way.
This document has been written with the anticipated original design
goals for traditional syslog in mind. The reason for a new layered
specification has arisen because standardization efforts for
reliable, and secure syslog extensions suffer from the lack of a
standards-track and transport independent RFC. Without this
document, each other standard needs to define its own syslog packet
format and transport mechanism, which over time will introduce subtle
compatibility issues. This document tries to provide a foundation
that syslog extensions can build on. This layered architecture
approach also provides a solid basis that allows code to be written
once for each syslog feature rather than once for each transport.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Conventions Used in This Document . . . . . . . . . . . . . . 6
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Basic Principles . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Example Deployment Scenarios . . . . . . . . . . . . . . . 8
5. Transport Layer Protocol . . . . . . . . . . . . . . . . . . . 10
5.1. Minimum Required Transport Mapping . . . . . . . . . . . . 10
6. Syslog Message Format . . . . . . . . . . . . . . . . . . . . 11
6.1. Message Length . . . . . . . . . . . . . . . . . . . . . . 12
6.2. HEADER . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2.1. PRI . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2.2. VERSION . . . . . . . . . . . . . . . . . . . . . . . 14
6.2.3. TIMESTAMP . . . . . . . . . . . . . . . . . . . . . . 14
6.2.4. HOSTNAME . . . . . . . . . . . . . . . . . . . . . . . 16
6.2.5. APP-NAME . . . . . . . . . . . . . . . . . . . . . . . 17
6.2.6. PROCID . . . . . . . . . . . . . . . . . . . . . . . . 17
6.2.7. MSGID . . . . . . . . . . . . . . . . . . . . . . . . 17
6.3. STRUCTURED-DATA . . . . . . . . . . . . . . . . . . . . . 18
6.3.1. SD-ELEMENT . . . . . . . . . . . . . . . . . . . . . . 18
6.3.2. SD-ID . . . . . . . . . . . . . . . . . . . . . . . . 18
6.3.3. SD-PARAM . . . . . . . . . . . . . . . . . . . . . . . 19
6.3.4. Change Control . . . . . . . . . . . . . . . . . . . . 19
6.3.5. Examples . . . . . . . . . . . . . . . . . . . . . . . 20
6.4. MSG . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 21
7. Structured Data IDs . . . . . . . . . . . . . . . . . . . . . 24
7.1. timeQuality . . . . . . . . . . . . . . . . . . . . . . . 24
7.1.1. tzKnown . . . . . . . . . . . . . . . . . . . . . . . 24
7.1.2. isSynced . . . . . . . . . . . . . . . . . . . . . . . 24
7.1.3. syncAccuracy . . . . . . . . . . . . . . . . . . . . . 24
7.1.4. Examples . . . . . . . . . . . . . . . . . . . . . . . 25
7.2. origin . . . . . . . . . . . . . . . . . . . . . . . . . . 25
7.2.1. ip . . . . . . . . . . . . . . . . . . . . . . . . . . 25
7.2.2. enterpriseId . . . . . . . . . . . . . . . . . . . . . 26
7.2.3. software . . . . . . . . . . . . . . . . . . . . . . . 26
7.2.4. swVersion . . . . . . . . . . . . . . . . . . . . . . 27
7.2.5. Example . . . . . . . . . . . . . . . . . . . . . . . 27
7.3. meta . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.3.1. sequenceId . . . . . . . . . . . . . . . . . . . . . . 27
7.3.2. sysUpTime . . . . . . . . . . . . . . . . . . . . . . 27
7.3.3. language . . . . . . . . . . . . . . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 29
8.1. UNICODE . . . . . . . . . . . . . . . . . . . . . . . . . 29
8.2. Control Characters . . . . . . . . . . . . . . . . . . . . 29
8.3. Message Truncation . . . . . . . . . . . . . . . . . . . . 30
8.4. Replaying . . . . . . . . . . . . . . . . . . . . . . . . 30
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8.5. Reliable Delivery . . . . . . . . . . . . . . . . . . . . 30
8.6. Message Integrity . . . . . . . . . . . . . . . . . . . . 31
8.7. Message Observation . . . . . . . . . . . . . . . . . . . 31
8.8. Inappropriate Configuration . . . . . . . . . . . . . . . 31
8.9. Forwarding Loop . . . . . . . . . . . . . . . . . . . . . 32
8.10. Load Considerations . . . . . . . . . . . . . . . . . . . 32
8.11. Denial of Service . . . . . . . . . . . . . . . . . . . . 33
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
9.1. VERSION . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.2. SD-IDs . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10. Working Group . . . . . . . . . . . . . . . . . . . . . . . . 36
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
12. Notes to the RFC Editor . . . . . . . . . . . . . . . . . . . 38
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
13.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 39
13.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 40
Appendix A. implementer Guidelines . . . . . . . . . . . . . . . 41
A.1. Relationship with BSD Syslog . . . . . . . . . . . . . . . 41
A.2. Message Length . . . . . . . . . . . . . . . . . . . . . . 42
A.3. Severity Values . . . . . . . . . . . . . . . . . . . . . 43
A.4. TIME-SECFRAC Precision . . . . . . . . . . . . . . . . . . 43
A.5. Case Convention for Names . . . . . . . . . . . . . . . . 43
A.6. Syslog Senders Without Knowledge of Time . . . . . . . . . 44
A.7. Notes on the timeQuality SD-ID . . . . . . . . . . . . . . 44
A.8. Additional Information on PROCID . . . . . . . . . . . . . 44
A.9. UTF-8 encoding and the BOM . . . . . . . . . . . . . . . . 45
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 46
Intellectual Property and Copyright Statements . . . . . . . . . . 47
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1. Introduction
This document describes a layered architecture for syslog. The goal
of this architecture is to separate message content from message
transport while enabling easy extensibility for each layer.
This document describes the standard format for syslog messages and
outlines the concept of transport mappings. It also describes
structured data elements, which can be used to transmit easily
parseable, structured information and allows for vendor extensions.
This document does not describe any storage format for syslog
messages. It is beyond of the scope of the syslog protocol and is
not necessary for system interoperability.
This document has been written with the anticipated original design
goals for traditional syslog in mind. The reason for a new layered
specification has arisen because standardization efforts for
reliable, and secure syslog extensions suffer from the lack of a
standards-track and transport independent RFC. Without this
document, each other standard would need to define its own syslog
packet format and transport mechanism which, over time will introduce
subtle compatibility issues. It tries to provide a foundation that
syslog extensions can build on. This layered architecture approach
also provides a solid basis that allows code to be written once
instead of once for each syslog feature.
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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 [4].
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3. Definitions
The following definitions are used in this document:
o An application that can generate a syslog message is called a
"sender".
o An application that can receive a syslog message is called a
"receiver".
o An application that can receive syslog messages and forward them
to another receiver is called a "relay".
o An application that receives messages and does not relay them to
any other receiver is called a "collector".
A single application can have multiple roles at the same time.
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4. Basic Principles
The following principles apply to syslog communication:
o The syslog protocol does not provide for any mechanism of
acknowledgement of message delivery. Though some transports may
provide status information, conceptually, syslog is a pure simplex
communications protocol.
o Senders send messages to receivers with no knowledge of whether
they are collectors or relays.
o Senders may be configured to send the same message to multiple
receivers.
o Relays may send all or some of the messages that they receive to a
subsequent relay or collector. They may also store or otherwise
locally process some or all messages without forwarding. In the
case where a receiver stores some messages and relays some
messages, it is acting as both a collector and a relay.
o Relays may also generate their own messages and send them on to
subsequent relays or collectors. In that case they are acting as
senders and a relay.
o Sender and receiver may reside on the same or different systems.
4.1. Example Deployment Scenarios
Sample deployment scenarios are shown in Diagram 1. Other
arrangements of these examples are also acceptable. As noted, in the
following diagram, relays may send all or some of the messages that
they receive and also send messages that they generate internally.
The boxes represent syslog-enabled applications.
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+------+ +---------+
|Sender|---->----|Collector|
+------+ +---------+
+------+ +-----+ +---------+
|Sender|---->----|Relay|---->----|Collector|
+------+ +-----+ +---------+
+------+ +-----+ +-----+ +---------+
|Sender|-->--|Relay|-->--..-->--|Relay|-->--|Collector|
+------+ +-----+ +-----+ +---------+
+------+ +-----+ +---------+
|Sender|---->----|Relay|---->----|Collector|
| |-+ +-----+ +---------+
+------+ \
\ +-----+ +---------+
+->--|Relay|---->----|Collector|
+-----+ +---------+
+------+ +---------+
|Sender|---->----|Collector|
| |-+ +---------+
+------+ \
\ +-----+ +---------+
+->--|Relay|---->----|Collector|
+-----+ +---------+
+------+ +-----+ +---------+
|Sender|---->----|Relay|---->-------|Collector|
| |-+ +-----+ +---| |
+------+ \ / +---------+
\ +-----+ /
+->--|Relay|-->--/
+-----+
+------+ +-----+ +---------+
|Sender|---->----|Relay|---->----------|Collector|
| |-+ +-----+ +--| |
+------+ \ / +---------+
\ +--------+ /
\ |+------+| /
+->-||Relay ||->---/
|+------|| /
||Sender||->-/
|+------+|
+--------+
Diagram 1. Some possible syslog deployment scenarios.
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5. Transport Layer Protocol
This document does not specify any transport layer protocol.
Instead, it describes the format of a syslog message in a transport
layer independent way. This requires that syslog transports be
defined in other documents. The first transport is defined in
RFCXXXX [14] and is consistent with the traditional UDP transport.
This transport is mandatory to implement for compliance to the
standard to support interoperability as the UDP transport has
historically been used for the transmission of syslog messages.
Any syslog transport protocol MUST NOT deliberately alter the syslog
message. If the transport protocol needs to perform temporary
transformations, these transformations MUST be reversed by the
transport protocol at the receiver, so that the upper layer will see
an exact copy of the message sent from the originator. Otherwise
cryptographic verifiers (such as signatures) will be broken. Of
course, message alteration might occur due to transmission errors or
other problems. Guarding against such alterations is not within the
scope of this effort.
5.1. Minimum Required Transport Mapping
All implementations of this specification MUST support a UDP-based
transport as described in RFCXXXX [14]. This is to provide a non-
disruptive transition path from devices that have historically
supported syslog over IPv4 UDP.
All implementations of this specification MUST also support a TLS-
based transport as described in RFCZZZZ [15].
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6. Syslog Message Format
The syslog message has the following ABNF [6] definition:
SYSLOG-MSG = HEADER SP STRUCTURED-DATA [SP MSG]
HEADER = PRI VERSION SP TIMESTAMP SP HOSTNAME
SP APP-NAME SP PROCID SP MSGID
PRI = "<" PRIVAL ">"
PRIVAL = 1*3DIGIT ; range 0 .. 191
VERSION = NONZERO-DIGIT 0*2DIGIT
HOSTNAME = NILVALUE / 1*255PRINTUSASCII
APP-NAME = NILVALUE / 1*48PRINTUSASCII
PROCID = NILVALUE / 1*128PRINTUSASCII
MSGID = NILVALUE / 1*32PRINTUSASCII
TIMESTAMP = NILVALUE / FULL-DATE "T" FULL-TIME
FULL-DATE = DATE-FULLYEAR "-" DATE-MONTH "-" DATE-MDAY
DATE-FULLYEAR = 4DIGIT
DATE-MONTH = 2DIGIT ; 01-12
DATE-MDAY = 2DIGIT ; 01-28, 01-29, 01-30, 01-31 based on
; month/year
FULL-TIME = PARTIAL-TIME TIME-OFFSET
PARTIAL-TIME = TIME-HOUR ":" TIME-MINUTE ":" TIME-SECOND
[TIME-SECFRAC]
TIME-HOUR = 2DIGIT ; 00-23
TIME-MINUTE = 2DIGIT ; 00-59
TIME-SECOND = 2DIGIT ; 00-59
TIME-SECFRAC = "." 1*6DIGIT
TIME-OFFSET = "Z" / TIME-NUMOFFSET
TIME-NUMOFFSET = ("+" / "-") TIME-HOUR ":" TIME-MINUTE
STRUCTURED-DATA = NILVALUE / 1*SD-ELEMENT
SD-ELEMENT = "[" SD-ID *(SP SD-PARAM) "]"
SD-PARAM = PARAM-NAME "=" %d34 PARAM-VALUE %d34
SD-ID = SD-NAME
PARAM-NAME = SD-NAME
PARAM-VALUE = UTF-8-STRING ; characters '"', '\' and
; ']' MUST be escaped.
SD-NAME = 1*32PRINTUSASCII
; except '=', SP, ']', %d34 (")
MSG = MSG-ANY / MSG-UTF8
MSG-ANY = *OCTET ; not starting with BOM
MSG-UTF8 = BOM UTF-8-STRING
BOM = %xEF.BB.BF
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UTF-8-STRING = *OCTET ; Any VALID UTF-8 String
; "shortest form" MUST be used
OCTET = %d00-255
SP = %d32
PRINTUSASCII = %d33-126
NONZERO-DIGIT = %d49-57
DIGIT = %d48 / NONZERO-DIGIT
NILVALUE = "-"
6.1. Message Length
Syslog message size limits are dictated by the syslog transport
mapping in use. There is no upper limit per se. Each transport
mapping MUST define the minimum maximum required message length
support. Any syslog transport mapping MUST support messages of up to
and including 480 octets in length.
Any syslog receiver MUST be able to accept messages of up to and
including 480 octets in length. All receiver implementations SHOULD
be able to accept messages of up to and including 2048 octets in
length. Receivers MAY receive messages larger than 2048 octets in
length. If a receiver receives a message with a length larger than
it supports, the receiver SHOULD truncate the payload.
Alternatively, it MAY discard the message.
If a receiver truncates messages, the truncation MUST occur at the
end of the message. After truncation, the message MAY contain
invalid UTF-8 encoding or invalid STRUCTURED-DATA. The receiver MAY
discard the message or MAY try to process as much as possible in this
case.
6.2. HEADER
The character set used in the HEADER MUST be seven-bit ASCII in an
eight-bit field as described in RFC 4234 [6]. These are the ASCII
codes as defined in "USA Standard Code for Information Interchange"
ANSI.X3-4.1968 [1].
The header format is designed to provide some interoperability with
older BSD-based syslog. For details on this, see Appendix A.1.
6.2.1. PRI
The PRI part MUST have three, four, or five characters and will be
bound with angle brackets as the first and last characters. The PRI
part starts with a leading "<" ('less-than' character, %d60),
followed by a number, which is followed by a ">" ('greater-than'
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character, %d62). The number contained within these angle brackets
is known as the Priority value (PRIVAL) and represents both the
Facility and Severity. The Priority value consists of one, two, or
three decimal integers (ABNF DIGITS) using values of %d48 (for "0")
through %d57 (for "9").
Facility and Severity values are not normative but often used. They
are described in the following tables for purely informational
purposes.
Numerical Facility
Code
0 kernel messages
1 user-level messages
2 mail system
3 system daemons
4 security/authorization messages
5 messages generated internally by syslogd
6 line printer subsystem
7 network news subsystem
8 UUCP subsystem
9 clock daemon
10 security/authorization messages
11 FTP daemon
12 NTP subsystem
13 log audit
14 log alert
15 clock daemon (note 2)
16 local use 0 (local0)
17 local use 1 (local1)
18 local use 2 (local2)
19 local use 3 (local3)
20 local use 4 (local4)
21 local use 5 (local5)
22 local use 6 (local6)
23 local use 7 (local7)
Table 1. syslog Message Facilities
Each message Priority also has a decimal Severity level indicator.
These are described in the following table along with their numerical
values.
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Numerical Severity
Code
0 Emergency: system is unusable
1 Alert: action must be taken immediately
2 Critical: critical conditions
3 Error: error conditions
4 Warning: warning conditions
5 Notice: normal but significant condition
6 Informational: informational messages
7 Debug: debug-level messages
Table 2. syslog Message Severities
The Priority value is calculated by first multiplying the Facility
number by 8 and then adding the numerical value of the Severity. For
example, a kernel message (Facility=0) with a Severity of Emergency
(Severity=0) would have a Priority value of 0. Also, a "local use 4"
message (Facility=20) with a Severity of Notice (Severity=5) would
have a Priority value of 165. In the PRI of a syslog message, these
values would be placed between the angle brackets as <0> and <165>
respectively. The only time a value of "0" follows the "<" is for
the Priority value of "0". Otherwise, leading "0"s MUST NOT be used.
6.2.2. VERSION
The VERSION field denotes the version of the syslog protocol
specification. The version number MUST be incremented for any new
syslog protocol specification that changes any part of the HEADER
format. Changes include the addition or removal of fields, or a
change of syntax or semantics of existing fields. This document uses
a VERSION value of "1". The VERSION values are IANA-assigned
(Section 9.1) via the Standards Action method as described in RFC
2434 [8].
6.2.3. TIMESTAMP
The TIMESTAMP field is a formalized timestamp derived from RFC 3339
[7].
Whereas RFC 3339 [7] makes allowances for multiple syntaxes, this
document imposes further restrictions. The TIMESTAMP value MUST
follow these restrictions:
o The "T" and "Z" characters in this syntax MUST be upper case.
o Usage of the "T" character is REQUIRED.
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o Leap seconds MUST NOT be used.
The sender SHOULD include TIME-SECFRAC if its clock accuracy and
performance permit. The "timeQuality" SD-ID described in Section 7.1
allows the sender to specify accuracy and trustworthiness of the
timestamp.
A syslog sender incapable of obtaining system time MUST use the
NILVALUE as TIMESTAMP.
6.2.3.1. Examples
Example 1
1985-04-12T23:20:50.52Z
This represents 20 minutes and 50.52 seconds after the 23rd hour of
12 April 1985 in UTC.
Example 2
1985-04-12T19:20:50.52-04:00
This represents the same time as in example 1, but expressed in the
Eastern US time zone (daylight savings time being observed).
Example 3
2003-10-11T22:14:15.003Z
This represents 11 October 2003 at 10:14:15pm, 3 milliseconds into
the next second. The timestamp is in UTC. The timestamp provides
millisecond resolution. The creator may have actually had a better
resolution, but by providing just three digits for the fractional
part of a second, it does not tell us.
Example 4
2003-08-24T05:14:15.000003-07:00
This represents 24 August 2003 at 05:14:15am, 3 microseconds into the
next second. The microsecond resolution is indicated by the
additional digits in TIME-SECFRAC. The timestamp indicates that its
local time is -7 hours from UTC. This timestamp might be created in
the US Pacific time zone during daylight savings time.
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Example 5 - An Invalid TIMESTAMP
2003-08-24T05:14:15.000000003-07:00
This example is nearly the same as Example 4, but it is specifying
TIME-SECFRAC in nanoseconds. This results in TIME-SECFRAC being
longer than the allowed 6 digits, which invalidates it.
6.2.4. HOSTNAME
The HOSTNAME field identifies the machine that originally sent the
syslog message.
The HOSTNAME field SHOULD contain the host name and the domain name
of the originator in the format specified in STD 13 [2]. This format
is called a Fully Qualified Domain Name (FQDN) in this document.
In practice, not all senders are able to provide a FQDN. As such,
other values MAY also be present in HOSTNAME. This document makes
provisions for using other values in such situations. A sender
SHOULD provide the most specific available value first. The order of
preference for the contents of the HOSTNAME field is as follows:
1. FQDN
2. Static IP address
3. hostname
4. Dynamic IP address
5. the NILVALUE
If an IPv4 address is used, it MUST be in the format of the dotted
decimal notation as used in STD 13 [3]. If an IPv6 address is used,
a valid textual representation as described in RFC 4291 [9], Section
2.2, MUST be used.
Senders SHOULD consistently use the same value in the HOSTNAME field
for as long as possible. If the sender uses IP addresses inside
hostname, the following rules apply: If the sender is multihomed,
this value SHOULD be one of its actual IP addresses. If a sender is
running on a machine that has both statically and dynamically
assigned addresses, then that value SHOULD be from the statically
assigned addresses. As an alternative, the sender MAY use the IP
address of the interface that is used to send the message.
The NILVALUE SHOULD only be used when the sender has no way to obtain
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its real hostname. This situation is considered highly unlikely.
6.2.5. APP-NAME
The APP-NAME field SHOULD identify the device or application that
generated the message. It is a string without further semantics. It
is intended for filtering messages on the receiver.
The NILVALUE MAY be used when the sender has no idea of its APP-NAME
or cannot provide that information. It may be that a device may not
be able to provide that information either because of a local policy
decision, or because the information is not available, or not
applicable, on the device.
This field MAY be operator-assigned.
6.2.6. PROCID
The PROCID field SHOULD be used to provide the sender's process name
or process ID. The field does not have any specific syntax.
The NILVALUE MAY be used when the sender can not obtain its PROCID or
cannot provide it.
PROCID is primarily meaningful for analysis tools. Properly used, it
can enable log analyzers to detect which messages were generated by
the same sender process. For example, on a UNIX system the syslog
daemon (syslogd) might emit messages to the log. All messages logged
by the same syslogd process will bear the same PROCID. When the
syslog sender is restarted, the PROCID value MAY change. That may
enable the analysis script to detect the syslogd restart.
This field MAY be operator-assigned. Some non-normative additional
information about PROCID values can be found in Appendix A.8.
6.2.7. MSGID
The MSGID SHOULD identify the type of message. For example, a
firewall might use the MSGID "TCPIN" for incoming TCP traffic and the
MSGID "TCPOUT" for outgoing TCP traffic. Messages with the same
MSGID should reflect events of the same semantics. The MSGID itself
is a string without further semantics. It is intended for filtering
messages on the receiver.
The NILVALUE SHOULD be used when the sender does not intend to
provide a real MSGID.
This field MAY be operator-assigned.
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6.3. STRUCTURED-DATA
STRUCTURED-DATA transports data in a well defined, easily parseable
and interpretable format. There are multiple usage scenarios. For
example, it may transport meta-information about the syslog message
or application-specific information such as traffic counters or IP
addresses.
STRUCTURED-DATA can contain zero, one, or multiple structured data
elements, which are referred to as "SD-ELEMENT" in this document.
In case of zero structured data elements, the STRUCTURED-DATA field
MUST contain the NILVALUE.
The character set used in STRUCTURED-DATA MUST be seven-bit ASCII in
an eight-bit field as described in RFC 4234 [6]. These are the ASCII
codes as defined in "USA Standard Code for Information Interchange"
ANSI.X3-4.1968 [1]. An exception is the PARAM-VALUE field (see
Section 6.3.3), in which UTF-8 encoding MUST be used.
A receiver MAY ignore malformed STRUCTURED-DATA elements. A relay
MUST forward malformed STRUCTURED-DATA without any alteration.
6.3.1. SD-ELEMENT
A SD-ELEMENT consists of a name and parameter name-value pairs. The
name is referred to as SD-ID. The name-value pairs are referred to
as "SD-PARAM".
6.3.2. SD-ID
SD-IDs are case-sensitive and uniquely identify the type and purpose
of the SD-ELEMENT. The same SD-ID MUST NOT exist more than once in a
message.
There are two formats for SD-ID names:
o Names that do not contain an at-sign ("@", ABNF %d64) are reserved
to be assigned by IETF CONSENSUS as described in BCP26 (RFC2434)
[8]. Currently, these are the names defined in Section 7. Names
of this format are only valid if they are first registered with
the IANA. Registered names MUST NOT contain an at-sign ('@', ABNF
%d64), an equal-sign ('=', ABNF %d61), a closing brace (']', ABNF
%d93), a quote-character ('"', ABNF %d34), or whitespace, or
control characters (ASCII code 127 and codes 32 or less).
o Anyone can define additional SD-IDs using names in the format
name@enterpriseId, e.g., "ourSDID@0". The format of the part
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preceding the at-sign is not specified, however these names MUST
be printable US-ASCII strings, and MUST NOT contain the equal-sign
('=', ABNF %d61), a closing brace (']', ABNF %d93), a quote-
character ('"', ABNF %d34), or whitespace, or control characters.
The part following the at-sign MUST be an enterpriseId as
specified in Section 7.2.2.
6.3.3. SD-PARAM
Each SD-PARAM consist of a name, referred to as PARAM-NAME, and a
value, referred to as PARAM-VALUE.
PARAM-NAME is case-sensitive. IANA controls all PARAM-NAMEs, with
the exception of those in SD-IDs whose names contain an at-sign. The
PARAM-NAME scope is within a specific SD-ID. Thus, equally-named
PARAM-NAME values contained in two different SD-IDs are not the same.
To support international characters, the PARAM-VALUE field MUST be
encoded using UTF-8. A sender MAY issue any valid UTF-8 sequence. A
receiver MUST accept any valid UTF-8 sequence in the "shortest form".
It MUST NOT fail if control characters are present in PARAM-VALUE.
It MAY modify messages containing control characters (e.g. by
changing an octet with value 0 (USASCII NUL) to the four characters
"#000"). For the reasons outlined in UNICODE TR36 [12], section 3.1,
a sender MUST encode messages in the "shortest form" and a receiver
MUST NOT interpret messages in the "non-shortest form".
Inside PARAM-VALUE, the characters '"' (ABNF %d34), '\' (ABNF %d92)
and ']' (ABNF %d93) MUST be escaped. This is necessary to avoid
parsing errors. Escaping ']' would not strictly be necessary but is
REQUIRED by this specification to avoid parser implementation errors.
Each of these three characters MUST be escaped as '\"', '\\' and '\]'
respectively. The backslash is used for control character escaping
for consistency with its use for escaping in other parts of the
syslog message as well as in traditional syslog.
A backslash ('\') followed by none of the three described characters
is considered an invalid escape sequence. In this case, the
backslash MUST be treated as a regular backslash and the following
character as a regular character. Thus, the invalid sequence MUST
not be altered.
A SD-PARAM MAY be repeated multiple times inside a SD-ELEMENT.
6.3.4. Change Control
Once SD-IDs and PARAM-NAMEs are defined, syntax and semantics of
these objects MUST NOT be altered. Should a change to an existing
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object be desired, a new SD-ID or PARAM-NAME MUST be created and the
old one remain unchanged. OPTIONAL PARAM-NAMEs MAY be added to an
existing SD-ID.
6.3.5. Examples
All examples in this section show only the structured data part of
the message. Examples should be considered to be on one line. They
are wrapped on multiple lines in this document for readability
purposes only. A description is given after each example.
Example 1 - Valid
[exampleSDID@0 iut="3" eventSource="Application"
eventID="1011"]
This example is a structured data element with a non-IANA controlled
SD-ID of type "exampleSDID@0" which has three parameters.
Example 2 - Valid
[exampleSDID@0 iut="3" eventSource="Application"
eventID="1011"][examplePriority@0 class="high"]
This is the same example as in 1, but with a second structured data
element. Please note that the structured data element immediately
follows the first one (there is no SP between them).
Example 3 - Invalid
[exampleSDID@0 iut="3" eventSource="Application"
eventID="1011"] [examplePriority@0 class="high"]
This is nearly the same example as 2, but it has a subtle error.
Please note that there is a SP character between the two structured
data elements ("]SP["). This is invalid. It will cause the
STRUCTURED-DATA field to end after the first element. The second
element will be interpreted as part of the MSG field.
Example 4 - Invalid
[ exampleSDID@0 iut="3" eventSource="Application"
eventID="1011"][examplePriority@0 class="high"]
This example again is nearly the same as 2. It has another subtle
error. Please note the SP character after the initial bracket. A
structured data element SD-ID MUST immediately follow the beginning
bracket, so the SP character invalidates the STRUCTURED-DATA. Thus,
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the receiver MAY discard this message.
Example 5 - Valid
[sigSig ver="1" rsID="1234" ... signature="..."]
Example 5 is a valid example. It shows a hypothetical IANA-assigned
SD-ID. Please note that the ellipses denote missing content, which
has been left out of this document for brevity.
6.4. MSG
The MSG part contains a free-form message that provides information
about the event.
The character set used in MSG SHOULD be UNICODE, encoded using UTF-8
as specified in RFC 3629 [5]. If the sender can not encode the MSG
in Unicode, it MAY use any other encoding.
The sender SHOULD avoid octet values below 32 (the traditional US-
ASCII control character range except DEL). These values are legal,
but a receiver MAY modify these characters upon reception. For
example, it might change them into an escape sequence (e.g. value 0
may be changed to "\0"). A receiver SHOULD NOT modify any other
octet values.
If a sender encodes MSG in UTF-8, the string MUST start with the
Unicode byte order mask (BOM), which for UTF-8 is ABNF %xEF.BB.BF.
The sender MUST encode in the "shortest form" and MAY use any valid
UTF-8 sequence.
If a receiver receives a MSG starting with a BOM, then it MUST be
interpreted as being encoded in UTF-8 for the reasons outlined in
UNICODE TR36 [12], section 3.1. If a sender does not encode MSG in
UTF-8, the string MUST NOT start with the Unicode BOM. Guidance
about this is given in Appendix A.9.
Also, according to UNICODE TR36 [12], a receiver MUST NOT interpret
messages in the "non-shortest form". It MUST NOT interpret invalid
UTF-8 sequences.
6.5. Examples
The following are examples of valid syslog messages. A description
of each example can be found below it. The examples are based on
similar examples from RFC 3164 [16] and may be familiar to readers.
The otherwise-unprintable Unicode BOM is represented as "BOM" in the
examples.
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Example 1
<34>1 2003-10-11T22:14:15.003Z mymachine.example.com su - ID47
- BOM'su root' failed for lonvick on /dev/pts/8
In this example, the VERSION is 1 and the Facility has the value of
4. The severity is 2. The message was created on 11 October 2003 at
10:14:15pm UTC, 3 milliseconds into the next second. The message
originated from a host that identifies itself as
"mymachine.example.com". The APP-NAME is "su" and the PROCID is
unknown. The MSGID is "ID47". The MSG is "'su root' failed for
lonvick...", encoded in UTF-8. The encoding is defined by the BOM.
There is no STRUCTURED-DATA present in the message, this is indicated
by "-" in the STRUCTURED-DATA field. The MSG is "'su root' failed
for lonvick...".
Example 2
<165>1 2003-08-24T05:14:15.000003-07:00 192.0.2.1
myproc 8710 - - %% It's time to make the do-nuts.
In this example, the VERSION is again 1. The Facility is 20, the
Severity 5. The message was created on 24 August 2003 at 5:14:15am,
with a -7 hour offset from UTC, 3 microseconds into the next second.
The HOSTNAME is "192.0.2.1", so the sender did not know its FQDN and
used one of its IPv4 addresses instead. The APP-NAME is "myproc" and
the PROCID is "8710" (for example this could be the UNIX PID). There
is no STRUCTURED-DATA present in the message, this is indicated by
"-" in the STRUCTURED-DATA field. There is no specific MSGID and
this is indicated by the "-" in the MSGID field. The message is "%%
It's time to make the do-nuts.". As the Unicode BOM is missing, the
receiver does not know the encoding of the MSG part.
Example 3 - with STRUCTURED-DATA
<165>1 2003-10-11T22:14:15.003Z mymachine.example.com
evntslog - ID47 [exampleSDID@0 iut="3" eventSource=
"Application" eventID="1011"] BOMAn application
event log entry...
This example is modeled after example 1. However, this time it
contains STRUCTURED-DATA, a single element with the value
"[exampleSDID@0 iut="3" eventSource="Application" eventID="1011"]".
The MSG itself is "An application event log entry..." Please note
that the BOM at the beginning of MSG indicates UTF-8 encoding.
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Example 4 - STRUCTURED-DATA Only
<165>1 2003-10-11T22:14:15.003Z mymachine.example.com
evntslog - ID47 [exampleSDID@0 iut="3" eventSource=
"Application" eventID="1011"][examplePriority@0
class="high"]
This example shows a message with only STRUCTURED-DATA and no MSG
part. This is a valid message.
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7. Structured Data IDs
This section defines the initial IANA-registered SD-IDs. See
Section 6.3 for a definition of structured data elements. All SD-IDs
defined here are OPTIONAL.
In some of the following, a maximum length is quantified for the
parameter values. In each of those cases, the receiver MUST be
prepared to receive the number of defined characters in any valid
UTF-8 code point. Since each character may be up to 6 octets, it is
RECOMMENDED that each receiver be prepared to receive up to six
octets per character.
7.1. timeQuality
The SD-ID "timeQuality" MAY be used by the original sender to
describe its notion of system time. This SD-ID SHOULD be written if
the sender is not properly synchronized with a reliable external time
source or if it does not know whether or not its time zone
information is correct. The main use of this structured data element
is to provide some information on the level of trust it has in the
TIMESTAMP described in Section 6.2.3. All parameters are OPTIONAL.
7.1.1. tzKnown
The "tzKnown" parameter indicates whether the original sender knows
its time zone. If it does so, the value "1" MUST be used. If the
time zone information is in doubt, the value "0" MUST be used. If
the sender knows its time zone but decides to emit time in UTC, the
value "1" MUST be used (because the time zone is known).
7.1.2. isSynced
The "isSynced" parameter indicates whether the original sender is
synchronized to a reliable external time source, e.g., via NTP. If
the original sender is time synchronized, the value "1" MUST be used.
If not, the value "0" MUST be used.
7.1.3. syncAccuracy
The "syncAccuracy" parameter indicates how accurate the original
sender thinks its time synchronization is. It is an integer
describing the maximum number of microseconds that its clock may be
off between synchronization intervals.
If the value "0" is used for "isSynced", this parameter MUST NOT be
specified. If the value "1" is used for "isSynced" but the
"syncAccuracy" parameter is absent, a receiver MUST assume that the
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time information provided is accurate enough to be considered
correct. The "syncAccuracy" parameter MUST be written only if the
original sender actually has knowledge of the reliability of the
external time source. In practice, in most cases, it will gain this
in-depth knowledge through operator configuration.
7.1.4. Examples
The following is an example of a system that does not know its time
zone nor whether it is being synchronized:
[timeQuality tzKnown="0" isSynced="0"]
With this information, the sender indicates that its time information
is unreliable. This may be a hint for the receiver to use its local
time instead of the message-provided TIMESTAMP for correlation of
multiple messages from different senders.
The following is an example of a system that knows its time zone and
knows that it is properly synchronized to a reliable external source:
[timeQuality tzKnown="1" isSynced="1"]
The following is an example of a system that knows both its time zone
and that it is externally synchronized. It also knows the accuracy
of the external synchronization:
[timeQuality tzKnown="1" isSynced="1" syncAccuracy="60000000"]
The difference between this and the previous example is that the
sender expects that its clock will be kept within 60 seconds of the
official time. Thus if the sender reports it is 9:00:00, it is no
earlier than 8:59:00 and no later then 9:01:00.
7.2. origin
The SD-ID "origin" MAY be used to indicate the origin of a syslog
message. The following parameters can be used. All parameters are
OPTIONAL.
Specifying any of these parameters is primarily an aid to log
analyzers and similar applications.
7.2.1. ip
The "ip" parameter denotes an IP address that the sender knows it had
at the time of sending the message. It MUST contain the textual
representation of an IP address as outlined in Section 6.2.4.
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This parameter can be used to provide additional identifying
information to what is present in the HOSTNAME field. It might be
especially useful if the host's IP address is included in the message
while the HOSTNAME field still contains the FQDN. It is also useful
for describing all IP addresses of a multihomed host.
If a sender has multiple IP addresses, it MAY either list one of its
IP addresses in the "ip" parameter or it MAY include multiple "ip"
parameters in a single "origin" structured data element.
7.2.2. enterpriseId
The "enterpriseId" parameter MUST be a 'SMI Network Management
Private Enterprise Code', maintained by IANA, whose prefix is
iso.org.dod.internet.private.enterprise (1.3.6.1.4.1). The number
that follows is unique and may be registered by an on-line form at
<http://www.iana.org/cgi-bin/mod_ent.pl>. An enterprise is only
authorized to assign values within the
iso.org.dod.internet.private.enterprise.<enterprise ID> subtree
assigned by IANA to that enterprise. The enterpriseId MUST contain
only a value from the
iso.org.dod.internet.private.enterprise.<enterprise ID> subtree. In
general, only the IANA-assigned enterpriseID is needed (a single
number). An enterprise might decide to use sub-identifiers below its
enterpriseID. If sub-identifiers are used, they MUST be separated by
periods and be represented as decimal numbers. An example for that
would be "0.1.2". Please note that the id "0.1.2" is just an example
and MUST NOT be used. The complete up-to-date list of Enterprise
Numbers is maintained by IANA at
<http://www.iana.org/assignments/enterprise-numbers>.
By specifying an enterpriseId, the vendor allows more specific
parsing of the message.
7.2.3. software
The "software" parameter uniquely identifies the software that
generated the message. If it is used, "enterpriseId" SHOULD also be
specified, so that a specific vendor's software can be identified.
The "software" parameter is not the same as the APP-NAME header
field. It MUST always contain the name of the generating software,
whereas APP-NAME can contain anything else, including an operator-
configured value.
The "software" parameter is a string. It MUST NOT be longer than 48
characters.
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7.2.4. swVersion
The "swVersion" parameter uniquely identifies the version of the
software that generated the message. If it is used, the "software"
and "enterpriseId" parameters SHOULD be provided, too.
The "swVersion" parameter is a string. It MUST NOT be longer than 32
characters.
7.2.5. Example
The following is an example with multiple IP addresses:
[origin ip="192.0.2.1" ip="192.0.2.129"]
In this example, the sender indicates that it has two ip addresses,
one being 192.0.2.1 and the other one being 192.0.2.129.
7.3. meta
The SD-ID "meta" MAY be used to provide meta-information about the
message. The following parameters can be used. All parameters are
OPTIONAL. If the "meta" SD-ID is used, at least one parameter SHOULD
be specified.
7.3.1. sequenceId
The "sequenceId" parameter tracks the sequence in which the sender
sent the messages. It is an integer that MUST be set to 1 when the
syslog function is started and MUST be increased with every message
up to a maximum value of 2147483647. If that value is reached, the
next message MUST be sent with a sequenceId of 1.
7.3.2. sysUpTime
The "sysUpTime" parameter MAY be used to include the SNMP "sysUpTime"
parameter in the message. Its syntax and semantics are as defined in
RFC 3418 [11].
As syslog does not support the SNMP "INTEGER" syntax directly, the
value MUST be represented as a decimal integer (no decimal point)
using only the characters "0", "1", "2", "3", "4", "5", "6", "7",
"8", and "9".
Note that the semantics in RFC3418 are "The time (in hundredths of a
second) since the network management portion of the system was last
re-initialized." This of course relates to the SNMP-related
management portion of the system, which MAY be different than the
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syslog-related management portion of the system.
7.3.3. language
The "language" parameter MAY be specified if the sender intends to
convey information about the natural language used inside MSG. If it
is specified, it MUST contain a two letter language identifier as
defined in ISO 639 [13].
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8. Security Considerations
8.1. UNICODE
This document uses UTF-8 encoding for the PARAM-VALUE and MSG fields.
There are a number of security issues with UNICODE. Any implementer
and operator is advised to review UNICODE TR36 [12] (UTR36) to learn
about these issues. This document guards against the technical
issues outlined in UTR36 by REQUIRING "shortest form" encoding both
for senders and receivers. However, the visual spoofing due to
character confusability still persists. This document tries to
minimize the effects of visual spoofing by allowing UNICODE only
where local script is expected and needed. In all other fields, US-
ASCII is REQUIRED. Also, the PARAM-VALUE and MSG fields should not
be the primary source for identifying information, further reducing
the risks associated with visual spoofing.
8.2. Control Characters
This document does not impose any mandatory restrictions on the MSG
or PARAM-VALUE content. As such, they MAY contain control
characters, including the NUL character.
In some programming languages (most notably C and C++), the NUL
character (ABNF %d00) traditionally has a special significance as
string terminator. Most, if not all, implementations of these
languages assume that a string will not extend beyond the first NUL
character. This is primarily a restriction of the supporting run-
time libraries. Please note that this restriction is often carried
over to programs and script languages written in those languages. As
such, NUL characters must be considered with great care and be
properly handled. An attacker may deliberately include NUL
characters to hide information after them. Incorrect handling of the
NUL character may also invalidate cryptographic checksums that are
transmitted inside the message.
Many popular text editors are also written in languages with this
restriction. Encoding NUL characters when writing to text files is
advisable. If they are stored without encoding, the file can
potentially become unreadable.
The same is true for other control characters. For example, an
attacker may deliberately include backspace characters to render
parts of the log message unreadable. Similar issues exist for almost
all control characters.
Finally, invalid UTF-8 sequences may be used by an attacker to inject
ASCII control characters.
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This specification permits a receiver to reformat control characters
received. Among others, the security risks associated with control
characters were an important driving force behind this restriction.
Senders are advised to not send control characters so that the
message text is not altered by any process on the receiver.
8.3. Message Truncation
Message truncation can be misused by an attacker to hide vital log
information. Messages over the minimum supported size may be
discarded or truncated by the receiver or interim systems. As such,
vital log information may be lost.
In order to prevent information loss, messages should not be longer
than the minimum maximum size required by Section 6.1. For best
performance and reliability, messages should be as small as possible.
Important information should be placed as early in the message as
possible because information at the beginning of the message is less
likely to be discarded by a size-limited receiver.
A sender should limit the size of any user-supplied data within a
syslog message. If it does not, an attacker may provide large data
in hopes of exploiting a potential weakness.
8.4. Replaying
There is no mechanism in the syslog protocol to detect message reply.
An attacker may record a set of messages that indicate normal
activity of a machine. At a later time, that attacker may remove
that machine from the network and replay the syslog messages to the
receiver. Even with the TIMESTAMP field in the HEADER part, an
attacker may record the packets and could simply modify them to
reflect the current time before retransmitting them. The
administrators may find nothing unusual in the received messages, and
their receipt would falsely indicate normal activity of the machine.
Cryptographically signing messages could prevent the alteration of
TIMESTAMPs and thus the replay attack.
8.5. Reliable Delivery
Because there is no mechanism described within this document to
ensure delivery, and the underlying transport may be unreliable
(e.g., UDP), and some messages may be lost. They may either be
dropped through network congestion, or they may be maliciously
intercepted and discarded. The consequences of dropping one or more
syslog messages cannot be determined. If the messages are simple
status updates, then their non-receipt may either not be noticed, or
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it may cause an annoyance for the system operators. On the other
hand, if the messages are more critical, then the administrators may
not become aware of a developing and potentially serious problem.
Messages may also be intercepted and discarded by an attacker as a
way to hide unauthorized activities.
It may be desirable to use a transport with guaranteed delivery to
mitigate congestion.
It may also be desirable to include rate-limiting features in syslog
senders. This can reduce potential congestion problems when message
bursts happen.
8.6. Message Integrity
Besides being discarded, syslog messages may be damaged in transit,
or an attacker may maliciously modify them. In such cases, the
original contents of the message will not be delivered to the
collector. Additionally, if an attacker is positioned between the
sender and collector of syslog messages, they may be able to
intercept and modify those messages while in-transit to hide
unauthorized activities.
8.7. Message Observation
While there are no strict guidelines pertaining to the MSG format,
most syslog messages are generated in human readable form with the
assumption that capable administrators should be able to read them
and understand their meaning. The syslog protocol does not have
mechanisms to provide confidentiality for the messages in transit.
In most cases passing clear-text messages is a benefit to the
operations staff if they are sniffing the packets off of the wire.
The operations staff may be able to read the messages and associate
them with other events seen from other packets crossing the wire to
track down and correct problems. Unfortunately, an attacker may also
be able to observe the human-readable contents of syslog messages.
The attacker may then use the knowledge gained from those messages to
compromise a machine or do other damage.
Operators are advised to use a secure transport mapping to avoid this
problem.
8.8. Inappropriate Configuration
Because there is no control information distributed about any
messages or configurations, it is wholly the responsibility of the
network administrator to ensure that the messages are actually going
to the intended recipients. Cases have been noted where senders were
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inadvertently configured to send syslog messages to the wrong
receivers. In many cases, the inadvertent receivers may not be
configured to receive syslog messages and it will probably discard
them. In certain other cases, the receipt of syslog messages has
been known to cause problems for the unintended recipient. If
messages are not going to the intended recipient, then they cannot be
reviewed or processed.
Using a reliable transport mapping can help identify some of these
problems. For example, it can identify a problem where a message
shall be sent to a system that is not configured to receive messages.
It can not identify sending messages to a wrong machine that is
accepting messages.
8.9. Forwarding Loop
As shown in Diagram 1, machines may be configured to relay syslog
messages to subsequent relays before reaching a collector. In one
particular case, an administrator found that he had mistakenly
configured two relays to forward messages with certain SEVERITY
values to each other. When either of these machines either received
or generated that type of message, it would forward it to the other
relay. That relay would, in turn, forward it back. This cycle did
cause degradation to the intervening network as well as to the
processing availability on the two devices. Network administrators
must take care not to cause such a death spiral.
8.10. Load Considerations
Network administrators must take the time to estimate the appropriate
capacity of the syslog receivers. An attacker may perform a Denial
of Service attack by filling the disk of the collector with false
messages. Placing the records in a circular file may alleviate this
but that has the consequence of not ensuring that an administrator
will be able to review the records in the future. Along this line, a
receiver or collector must have a network interface capable of
receiving all messages sent to it.
Administrators and network planners must also critically review the
network paths between the devices, the relays, and the collectors.
Generated syslog messages should not overwhelm any of the network
links.
In order to reduce the impact of this issue, using transports with
guaranteed delivery is recommended.
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8.11. Denial of Service
As with any system, an attacker may just overwhelm a receiver by
sending more messages to it than can be handled by the infrastructure
or the device itself. implementers should attempt to provide features
that minimize this threat, such as only accepting syslog messages
from known IP addresses.
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9. IANA Considerations
9.1. VERSION
IANA is requested to create a registry entitled "syslog version
values" of VERSION values as described in Section 6.2.2. Version
numbers MUST be incremented for any new syslog protocol specification
that changes any part of the HEADER. Changes include addition or
removal of fields or a change of syntax or semantics of existing
fields.
VERSION numbers must be registered via the Standards Action method as
described in RFC 2434 [8]. IANA is requested to register the
VERSIONs shown in table 4 below.
VERSION FORMAT
1 Defined in RFCYYYY
Table 4. IANA-registered VERSIONs.
9.2. SD-IDs
IANA is requested to create a registry entitled "syslog structured
data id values" of Structured Data ID (SD-ID) values together with
their associated PARAM-NAME values as described in Section 7.
New SD-ID and new PARAM-NAME values must be registered through the
IETF CONSENSUS method as described in RFC 2434 [8].
Once SD-IDs and SD-PARAMs are defined, syntax and semantics of these
objects MUST NOT be altered. Should a change to an existing object
be desired, a new SD-ID or SD-PARAM MUST be created and the old one
remain unchanged.
A provision is made here for locally extensible names. The IANA will
not register, and will not control names with the at-sign (ABNF %d64)
in them.
IANA is requested to register the SD-IDs and PARAM-NAMEs shown in
table 5 below.
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SD-ID PARAM-NAME
timeQuality OPTIONAL
tzKnown OPTIONAL
isSynced OPTIONAL
syncAccuracy OPTIONAL
origin OPTIONAL
ip OPTIONAL
enterpriseId OPTIONAL
software OPTIONAL
swVersion OPTIONAL
meta OPTIONAL
sequenceId OPTIONAL
sysUpTime OPTIONAL
language OPTIONAL
Table 5. IANA-registered SD-IDs and their PARAM-NAMEs.
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10. Working Group
The working group can be contacted via the mailing list:
syslog@ietf.org
The current Chairs of the Working Group may be contacted at:
Chris Lonvick
Cisco Systems
Email: clonvick@cisco.com
David Harrington
Huawei Technologies USA
Email: dbharrington@comcast.net
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11. Acknowledgments
The authors wish to thank Chris Lonvick, Jon Callas, Andrew Ross,
Albert Mietus, Anton Okmianski, Tina Bird, Devin Kowatch, David
Harrington, Sharon Chisholm, Richard Graveman, Tom Petch, Dado
Colussi, Clement Mathieu, Didier Dalmasso, and all other people who
commented on various versions of this proposal.
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12. Notes to the RFC Editor
This is a note to the RFC editor. This ID is submitted along with
draft-ietf-syslog-transport-udp and draft-ietf-syslog-transport-tls.
These documents cross-reference each other. When RFC numbers are
determined for each of these IDs, replace XXXX with the proper RFC
number for draft-ietf-syslog-transport-udp and replace ZZZZ with the
proper RFC number for draft-ietf-syslog-transport-tls and remove this
note.
This document uses the term "RFCYYYY" for self-references. When a
RFC number is assigned to it, replace YYYY with the proper RFC number
and remove this note.
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13. References
13.1. Normative
[1] American National Standards Institute, "USA Code for
Information Interchange", ANSI X3.4, 1968.
[2] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[3] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003.
[6] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
[7] Klyne, G., Ed. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[8] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[9] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[10] Chisholm, S. and D. Romascanu, "Alarm Management Information
Base (MIB)", RFC 3877, September 2004.
[11] Presuhn, R., "Management Information Base (MIB) for the Simple
Network Management Protocol (SNMP)", STD 62, RFC 3418,
December 2002.
[12] Davis, M. and M. Suignard, "UNICODE Security Considerations",
July 2005, <http://www.unicode.org/reports/tr36/tr36-3.html>.
[13] International Organization for Standardization, "Code for the
representation of names of languages", ISO Standard 639-1:2002,
July 2002.
[14] Okmianski, A., "Transmission of syslog messages over UDP",
RFC XXXX, November 2006.
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[15] Miao, F. and M. Yuzhi, "TLS Transport Mapping for SYSLOG",
RFC ZZZZ, August 2006.
13.2. Informative
[16] Lonvick, C., "The BSD Syslog Protocol", RFC 3164, August 2001.
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Appendix A. implementer Guidelines
Information in this section is given as an aid to implementers.
While this information is considered to be helpful, it is not
normative. As such, an implementation is NOT REQUIRED to follow it
in order to claim compliance to this specification.
A.1. Relationship with BSD Syslog
While BSD syslog is in widespread use, its format has never been
formally standardized. RFC 3164 [16] describes observed formats. It
is an INFORMATIONAL RFC, and practice shows that there are many
different implementations. Research during creation of this document
showed that there is very little in common between different syslog
implementations on different platforms. The only thing that all of
them agree upon is that messages start with "<" PRIVAL ">". Other
than that, legacy syslog messages are not formatted in a consistent
way. Consequently, RFC 3164 describes no specific elements inside a
syslog message. It states that any message destined to the syslog
UDP port must be treated as a syslog message, no matter what its
format or content is.
This document retains the PRI value syntax and semantics. This will
allow legacy syslog implementation to put messages generated by
senders compliant to this specification into the right bins.
Most existing implementations support UDP as the transport protocol
for syslog. This specification REQUIRES UDP support in compliant
implementations, and allows additional transport protocols to be
used.
RFC 3164 describes relay behavior. This document does not specify
relay behavior. This might be done in a separate document.
The TIMESTAMP described in RFC 3164 offers less precision than the
timestamp specified in this document. It also lacks the year and
time zone information. If a message formatted according to this
document needs to be reformatted to be in RFC 3164 format, it is
suggested that the sender's local time zone be used, and the time
zone information and the year be dropped. If a RFC 3164 formatted
message is received and must be transformed to be compliant to this
document, the current year should be added and the receiver's time
zone be assumed.
The HOSTNAME in RFC 3164 is less specific, but this format is still
supported in this document as one of the alternate HOSTNAME
representations.
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The MSG part of the message is described as TAG and CONTENT in RFC
3164. In this document, MSG is what was called CONTENT in RFC 3164.
The TAG is now part of the header, but not as a single field. The
TAG has been split into APP-NAME, PROCID, and MSGID. This does not
totally resemble the usage of TAG, but provides the same
functionality for most of the cases.
In RFC 3164, STRUCTURED-DATA was not described. If a message
compliant with this document contains STRUCTURED-DATA and must be
reformatted according to RFC 3164, the STRUCTURED-DATA simply becomes
part of the RFC 3164 CONTENT free-form text.
In general, this document tries to provide an easily parseable header
with clear field separations whereas traditional BSD syslog suffers
from some historically developed, hard to parse field separation
rules.
A.2. Message Length
Implementers should note the message size limitations outlined in
Section 6.1 and try to keep the most important parts early in the
message (within the minimum guaranteed length). This ensures they
will be seen by the receiver even if it (or a relay on the message
path) truncates the message.
The reason syslog receivers must only support receiving up to and
including 480 octets has, among other things, to do with difficult
delivery problems in a broken network. Syslog messages may use a UDP
transport mapping with this 480 octet restriction to avoid session
overhead and message fragmentation. In a network with problems, the
likelihood of getting one single-packet message delivered
successfully is higher than getting two message fragments delivered
successfully. Therefore using a larger size may prevent the operator
from getting some critical information about the problem, whereas
using small messages might get that information to the operator. As
such, messages intended for troubleshooting purposes should not be
larger than 480 octets. To further strengthen this point, it has
also been observed that some UDP implementations generally do not
support message sizes of more then 480 octets. This behaviour is
very rare and may no longer be an issue.
There are other use cases where syslog messages are used to transmit
inherently lengthy information, e.g. audit data. By not enforcing
any upper limit on the message size, syslog senders and receivers can
be implemented with any size needed and still be compliant with this
document. In such cases, it is the operator's responsibility to
ensure that all components in a syslog infrastructure support the
required message sizes. Transport mappings may recommend specific
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message size limits that must be enforced.
Implementers are reminded that the message length is specified in
octets. There is a potentially large difference between the length
in characters and the length in octets for UTF-8 strings.
It must be noted that the IPv6 MTU is about 2.5 times 480. An
implementation targeted towards an IPv6-only environment might thus
assume this as a larger minimum size.
A.3. Severity Values
This section describes guidelines for using Severity as outlined in
Section 6.2.1.
All implementations should try to assign the most appropriate
severity to their message. Most importantly, messages designed to
enable debugging or testing of software should be assigned severity
7. Severity 0 should be reserved for messages of very high
importance (like serious hardware failures or imminent power
failure). An implementation may use severities 0 and 7 for other
purposes if this is configured by the administrator.
Because severities are very subjective, a receiver should not assume
that all senders have the same definition of severity.
A.4. TIME-SECFRAC Precision
The TIMESTAMP described in Section 6.2.3 supports fractional seconds.
This provides grounds for a very common coding error, where leading
zeros are removed from the fractional seconds. For example, the
TIMESTAMP "2003-10-11T22:13:14.003" may be erroneously written as
"2003-10-11T22:13:14.3". This would indicate 300 milliseconds
instead of the 3 milliseconds actually meant.
A.5. Case Convention for Names
Names are used at various places in this document, for example for
SD-IDs and PARAM-NAMEs. This document uses "lower camel case"
consistently. With that, each name begins with a lower case letter
and each new word starts with an upper case letter, but no hyphen or
other delimiter. An example of this is "timeQuality".
While an implementation is free to use any other case convention for
experimental names, it is suggested that the case convention outlined
above is followed.
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A.6. Syslog Senders Without Knowledge of Time
In Section 6.2.3, the NILVALUE has been allowed for usage by senders
without knowledge of time. This is done to support a special case
when a sender is not aware of time at all. It can be argued whether
such a sender can actually be found in today's IT infrastructure.
However, discussion has indicated that those things may exist in
practice and as such there should be a guideline established for this
case.
However, an implementation SHOULD emit a valid TIMESTAMP if the
underlying operating system, programming system, and hardware
supports a clock function. A proper TIMESTAMP should be emitted even
if it is difficult, but doable, to obtain the system time. The
NILVALUE should only be used when it is actually impossible to obtain
time information. This rule should not be used as an excuse for lazy
implementations.
A.7. Notes on the timeQuality SD-ID
It is recommended that the value of "0" be the default for the
"tzKnown" (Section 7.1.1) parameter. It should only be changed to
"1" after the administrator has specifically configured the time
zone. The value "1" may be used as the default if the underlying
operating system provides accurate time zone information. It is
still advised that the administrator explicitly acknowledge the
correctness of the time zone information.
It is important not to create a false impression of accuracy with the
timeQuality SD-ID (Section 7.1). A sender should only indicate a
given accuracy if it actually knows it is within these bounds. It is
generally assumed that the sender gains this in-depth knowledge
through operator configuration. As such, by default, an accuracy
should not be provided.
A.8. Additional Information on PROCID
The objective behind PROCID (Section 6.2.6) is to provide a quick way
to detect a new instance of the sender's syslog process. It must be
noted that this is not a reliable identification as a second sender
process may actually be assigned the same process ID as a previous
one. Properly used, PROCID can be helpful for analysis purposes.
While PROCID is defined to contain the sender's process ID, it is up
to the sender to decide what this ID is. For example, on a general
purpose OS, it might actually be the operating system process ID of
the syslog sender's process. Other syslog senders might decide that
it is more appropriate to put an internal identification into PROCID.
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For example, a SMTP MTA might not put the operating system process ID
into PROCID but might prefer to put its SMTP transaction ID into
PROCID. This might be very useful, because it allows the receiver to
group messages based on the SMTP transaction, which could also be
called the SMTP "process" in this case. On an embedded system
without any operating system process ID, PROCID might actually be a
reboot ID, which might be the closest thing to a process ID on this
hypothetical embedded system.
A.9. UTF-8 encoding and the BOM
This document specifies that SD-PARAMS must always be encoded in
UTF-8. Other encodings of the message in the MSG portion, including
ASCIIPRINT, are not permitted by a device conforming to this
specification. There are two cases that need to be addressed here.
First, a syslog process conforming to this specification may not be
able to ascertain that the information given to it from a process is
encoded in UTF-8. If it cannot determine that with certainty, the
syslog process may choose to not incorporate the BOM in the MSG. If
the syslog process has a good indication that the content of the
message is encoded in UTF-8 then it should include the BOM. In the
second case, a syslog process may be relaying a message from a device
that does not comform to this specification. In that case, the
device would likely not include the BOM unless it has ascertained
that the received message was encoded in UTF-8.
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Author's Address
Rainer Gerhards
Adiscon GmbH
Mozartstrasse 21
Grossrinderfeld, BW 97950
Germany
Email: rgerhards@adiscon.com
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Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
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