SIPPING V. Gurbani, Ed.
Internet-Draft Bell Laboratories, Alcatel-Lucent
Intended status: Informational E. Burger, Ed.
Expires: December 10, 2010 This space for sale
T. Anjali
Illinois Institute of Technology
H. Abdelnur
O. Festor
INRIA
June 8, 2010
The Common Log Format (CLF) for the Session Initiation Protocol (SIP)
draft-ietf-sipclf-problem-statement-02
Abstract
Well-known web servers such as Apache and web proxies like Squid
support event logging using a common log format. The logs produced
using these de-facto standard formats are invaluable to system
administrators for trouble-shooting a server and tool writers to
craft tools that mine the log files and produce reports and trends.
Furthermore, these log files can also be used to train anomaly
detection systems and feed events into a security event management
system. The Session Initiation Protocol does not have a common log
format, and as a result, each server supports a distinct log format
that makes it unnecessarily complex to produce tools to do trend
analysis and security detection. We propose a common log file format
for SIP servers that can be used uniformly by proxies, registrars,
redirect servers as well as back-to-back user agents.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
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The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on December 10, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem statement . . . . . . . . . . . . . . . . . . . . . . 4
4. What SIP CLF is and what it is not . . . . . . . . . . . . . . 4
5. Alternative approaches to SIP CLF . . . . . . . . . . . . . . 5
5.1. SIP CLF and CDRs . . . . . . . . . . . . . . . . . . . . . 5
5.2. SIP CLF and Wireshark packet capture . . . . . . . . . . . 6
6. Motivation and use cases . . . . . . . . . . . . . . . . . . . 6
7. Challenges in establishing a SIP CLF . . . . . . . . . . . . . 8
8. Data model . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. SIP CLF data model elements for an UAC . . . . . . . . . . 11
8.2. SIP CLF data model elements for an UAS . . . . . . . . . . 11
8.3. SIP CLF data model elements for a proxy . . . . . . . . . 11
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. UAC registering with a proxy . . . . . . . . . . . . . . . 13
9.2. Direct call between Alice and Bob . . . . . . . . . . . . 14
9.3. Single downstream branch call . . . . . . . . . . . . . . 14
9.4. Forked call . . . . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 19
11. Operational guidance . . . . . . . . . . . . . . . . . . . . . 21
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
14.1. Normative References . . . . . . . . . . . . . . . . . . . 22
14.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
RFC 3261 [RFC3261] defines additional terms used in this document
that are specific to the SIP domain such as "proxy"; "registrar";
"redirect server"; "user agent server" or "UAS"; "user agent client"
or "UAC"; "back-to-back user agent" or "B2BUA"; "dialog";
"transaction"; "server transaction".
2. Introduction
Servers executing on Internet hosts produce log records as part of
their normal operations. A log record is, in essence, a summary of
an application layer protocol data unit (PDU), that captures in
precise terms an event that was processed by the server. These log
records serve many purposes, including analysis and troubleshooting.
Well-known web servers such as Apache and Squid support event logging
using a Common Log Format (CLF), the common structure for logging
requests and responses serviced by the web server. It can be argued
that a good part of the success of Apache has been its CLF because it
allowed third parties to produce tools that analyzed the data and
generated traffic reports and trends. The Apache CLF has been so
successful that not only did it become the de-facto standard in
producing logging data for web servers, but also many commercial web
servers can be configured to produce logs in this format. An example
of Apache CLF is depicted next:
%h %l %u %t \"%r\" %s %b
remotehost rfc931 authuser [date] request status bytes
remotehost: Remote hostname (or IP number if DNS hostname is not
available, or if DNSLookup is Off.
rfc931: The remote logname of the user.
authuser: The username by which the user has authenticated himself.
[date]: Date and time of the request.
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request: The request line exactly as it came from the client.
status: The HTTP status code returned to the client.
bytes: The content-length of the document transferred.
The inspiration for the SIP CLF is the Apache CLF. However, the
state machinery for a HTTP transaction is much simpler than that of
the SIP transaction (as evidenced in Section 7). The SIP CLF needs
to do considerably more.
3. Problem statement
The Session Initiation Protocol [RFC3261](SIP) is an Internet
multimedia session signaling protocol that is increasingly used for
other services besides session establishment. A typical deployment
of SIP in an enterprise will consist of SIP entities from multiple
vendors. Currently, if these entities are capable of producing a log
file of the transactions being handled by them, the log files are
produced in a proprietary format. The result of multiplicity of the
log file formats is the inability of the support staff to easily
trace a call from one entity to another, or even to craft common
tools that will perform trend analysis, debugging and troubleshooting
problems uniformly across the SIP entities of multiple vendors.
SIP does not currently have a CLF format and this document serves to
provide the rationale to establish a SIP CLF and identifies the
required minimal information that must appear in any SIP CLF record.
4. What SIP CLF is and what it is not
The SIP CLF is a standardized manner of producing a log file. This
format can be used by SIP clients, SIP Servers, proxies, and B2BUAs.
The SIP CLF is simply an easily digestible log of currently occurring
events and past transactions. It contains enough information to
allow humans and automata to derive relationships between discrete
transactions handled at a SIP entity. For example, a SIP
administrator should be able to issue a concise command to discover
relationships between transactions or to search a certain dialog or
transaction.
Note: The exact form of the "concise command" is left unspecified
until the working group agrees to one or more formats for encoding
the fields.
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The SIP CLF is amenable to quick parsing (i.e., well-delimited
fields) and it is platform and operating system neutral.
The SIP CLF is amenable to easy parsing and lends itself well to
creating other innovative tools.
The SIP CLF is not a billing tool. It is not expected that
enterprises will bill customers based on SIP CLF. The SIP CLF
records events at the signaling layer only and does not attempt to
correlate the veracity of these events with the media layer. Thus,
it cannot be used to trigger customer billing.
The SIP CLF is not a quality of service (QoS) measurement tool. If
QoS is defined as measuring the mean opinion score (MOS) of the
received media, then SIP CLF does not aid in this task since it does
not summarize events at the media layer.
5. Alternative approaches to SIP CLF
It is perhaps tempting to consider other approaches --- which though
not standardized, are in wide enough use in networks today --- to
determine whether or not a SIP CLF would benefit a SIP network
consisting of multi-vendor products. The two existing approaches
that approximate what SIP CLF does are Call Detail Records (CDRs) and
Wireshark packet sniffing.
5.1. SIP CLF and CDRs
CDRs are used in operator networks widely and with the adoption of
SIP, standardization bodies such as 3GPP have subsequently defined
SIP-related CDRs as well. Today, CDRs are used to implement the
functionality approximated by SIP CLF, however, there are important
differences.
One, SIP CLF operates natively at the transaction layer and maintains
enough information in the information elements being logged that
dialog-related data can be subsequently derived from the transaction
logs. Thus, esoteric SIP fields and parameters like the To header,
including tags; the From header, including tags, the CSeq number,
etc. are logged in SIP CLF. By contrast, a CDR is used mostly for
charging and thus saves information to facilitate that very aspect.
A CDR will most certainly log the public user identification of a
party requesting a service (which may not correspond to the From
header) and the public user identification of the party called party
(which may not correspond to the To header.) Furthermore, the
sequence numbers maintained by the CDR may not correspond to the SIP
CSeq header. Thus it will be hard to piece together the state of a
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dialog through a sequence of CDR records.
Two, a CDR record will, in all probability, be generated at a SIP
entity performing some form of proxy-like functionality of a B2BUA
providing some service. By contrast, SIP CLF is light- weight enough
that it can be generated by a canonical SIP user agent server and
user agent client as well, including those that execute on resource
constrained devices (mobile phones).
Finally, SIP is also being deployed outside of operator- managed VoIP
networks. Universities, research laboratories, and small-to-medium
size companies are deploying SIP-based VoIP solutions on networks
owned and managed by them. Much of the latter constituencies will
not have an interest in generating CDRs, but they will like to have a
concise representation of the messages being handled by the SIP
entities in a common format.
5.2. SIP CLF and Wireshark packet capture
Wireshark is a popular raw packet capture tool. It contains filters
that can understand SIP at the protocol level and break down a
captured message into its individual header components. While
Wireshark is appropriate to capture and view discrete SIP messages,
it does not suffice to serve in the same capacity as SIP CLF for two
reasons.
First, while the Wireshark format saves bulk of the information
needed to create transaction and dialog state, the Wireshark format
is a binary format that does not lend itself very well to being
manipulated by text-based tools. Second and more importantly, if the
SIP messages are exchanged over a TLS-oriented transport, Wireshark
will be unable to decrypt them and render them as individual SIP
headers.
6. Motivation and use cases
As SIP becomes pervasive in multiple business domains and ubiquitous
in academic and research environments, it is beneficial to establish
a CLF for the following reasons:
Common reference for interpreting events: In a laboratory
environment or an enterprise service offering there will typically
be SIP entities from multiple vendors participating in routing
requests. Absent a CLF format, each entity will produce output
records in a native format making it hard to establish commonality
for tools that operate on the log file.
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Writing common tools: A CLF format allows independent tool providers
to craft tools and applications that interpret the CLF data to
produce insightful trend analysis and detailed traffic reports.
The format should be such that it retains the ability to be read
by humans and processed using traditional Unix text processing
tools.
Session correlation across diverse processing elements: In
operational SIP networks, a request will typically be processed by
more than one SIP server. A SIP CLF will allow the network
operator to trace the progression of the request (or a set of
requests) as they traverse through the different servers to
establish a concise diagnostic trail of a SIP session.
Note that tracing the request through a set of servers is
considerably less challenging if all the servers belong to the
same administrative domain.
Message correlation across transactions: A SIP CLF can enable a
quick lookup of all messages that comprise a transaction (e.g.,
"Find all messages corresponding to server transaction X,
including all forked branches.")
Message correlation across dialogs: A SIP CLF can correlate
transactions that comprise a dialog (e.g., "Find all messages for
dialog created by Call-ID C, From tag F and To tag T.")
Trend analysis: A SIP CLF allows an administrator to collect data
and spot patterns or trends in the information (e.g., "What is the
domain where the most sessions are routed to between 9:00 AM and
12:00 PM?")
Train anomaly detection systems: A SIP CLF will allow for the
training of anomaly detection systems that once trained can
monitor the CLF file to trigger an alarm on the subsequent
deviations from accepted patterns in the data set. Currently,
anomaly detection systems monitor the network and parse raw
packets that comprise a SIP message -- a process that is
unsuitable for anomaly detection systems [rieck2008]. With all
the necessary event data at their disposal, network operations
managers and information technology operation managers are in a
much better position to correlate, aggregate, and prioritize log
data to maintain situational awareness.
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Testing: A SIP CLF allows for automatic testing of SIP equipment by
writing tools that can parse a SIP CLF file to ensure behavior of
a device under test.
Troubleshooting: A SIP CLF can enable cursory trouble shooting of a
SIP entity (e.g., "How long did it take to generate a final
response for the INVITE associated with Call-ID X?")
Offline analysis: A SIP CLF allows for offline analysis of the data
gathered. Once a SIP CLF file has been generated, it can be
transported (subject to the security considerations in Section 10)
to a host with appropriate computing resources to perform
subsequent analysis.
Real-time monitoring: A SIP CLF allows administrators to visually
notice the events occurring at a SIP entity in real-time providing
accurate situational awareness.
7. Challenges in establishing a SIP CLF
Establishing a CLF for SIP is a challenging task. The behavior of a
SIP entity is more complex when compared to the equivalent HTTP
entity.
Base protocol services such as parallel or serial forking elicit
multiple final responses. Ensuing delays between sending a request
and receiving a final response all add complexity when considering
what fields should comprise a CLF and in what manner. Furthermore,
unlike HTTP, SIP groups multiple discrete transactions into a dialog,
and these transactions may arrive at a varying inter-arrival rate at
a proxy. For example, the BYE transaction usually arrives much after
the corresponding INVITE transaction was received, serviced and
expunged from the transaction list. Nonetheless, it is advantageous
to relate these transactions such that automata or a human monitoring
the log file can construct a set consisting of related transactions.
ACK requests in SIP need careful consideration as well. In SIP, an
ACK is a special method that is associated with an INVITE only. It
does not require a response, and furthermore, if it is acknowledging
a non-2xx response, then the ACK is considered part of the original
INVITE transaction. If it is acknowledging a 2xx-class response,
then the ACK is a separate transaction consisting of a request only
(i.e., there is not a response for an ACK request.) CANCEL is
another method that is tied to an INVITE transaction, but unlike ACK,
the CANCEL request elicits a final response.
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While most requests elicit a response immediately, the INVITE request
in SIP can pend at a proxy as it forks branches downstream or at a
user agent server while it alerts the user. RFC 3261 [RFC3261]
instructs the server transaction to send a 1xx-class provisional
response if a final response is delayed for more than 200 ms. A SIP
CLF log file needs to include such provisional responses because they
help train automata associated with anomaly detection systems and
provide some positive feedback for a human observer monitoring the
log file.
Finally, beyond supporting native SIP actors such as proxies,
registrars, redirect servers, and user agent servers (UAS), it is
beneficial to derive a CLF format that supports back-to-back user
agent (B2BUA) behavior, which may vary considerably depending on the
specific nature of the B2BUA.
8. Data model
The following SIP CLF fields are defined as minimal information that
must appear in any SIP CLF record:
Timestamp: Date and time of the request or response represented as
the number of seconds and milliseconds since the Unix epoch.
Source:port: The DNS name or IP address of the upstream client,
including the port number. The port number must be separated from
the DNS name or IP address by a single ':'.
Destination:port: The DNS name or IP address of the downstream
server, including the port number. The port number must be
separated from the DNS name or IP address by a single ':'.
From: The From URI, including the tag. Whilst one may question the
value of the From URI in light of RFC4744 [RFC4474], the From URI,
nonetheless, imparts some information. For one, the From tag is
important and, in the case of a REGISTER request, the From URI can
provide information on whether this was a third-party registration
or a first-party one.
To: The To URI, including tag.
Callid: The Call-ID.
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CSeq: The CSeq header.
R-URI: The Request-URI, including any URI parameters.
Status: The SIP response status code.
SIP Proxies may fork, creating several client transactions that
correlate to a single server transaction. Responses arriving on
these client transactions, or new requests (CANCEL, ACK) sent on the
client transaction need log file entries that correlate with a server
transaction. Similarly, a B2BUA may create one or more client
transactions in response to an incoming request. These transactions
will require correlation as well. The last two data model elements
provide this correlation.
Server-Txn: Server transaction identification code - the transaction
identifier associated with the server transaction.
Implementations can reuse the server transaction identifier (the
topmost branch-id of the incoming request, with or without the
magic cookie), or they could generate a unique identification
string for a server transaction (this identifier needs to be
locally unique to the server only.) This identifier is used to
correlate ACKs and CANCELs to an INVITE transaction; it is also
used to aid in forking as explained later in this section. (See
Section 9 for usage.)
Client-Txn: Client transaction identification code - this field is
used to associate client transactions with a server transaction
for forking proxies or B2BUAs. Upon forking, implementations can
reuse the value they inserted into the topmost Via header's branch
parameter, or they can generate a unique identification string for
the client transaction. (See Section 9 for usage.)
Finally, the SIP CLF should be extensible such that future SIP
methods, headers and bodies can be represented as well. Besides the
mandatory fields listed above, all other SIP headers will appear as
an ordered pairs of header field names and values.
This data model applies to all SIP entities --- a UAC, UAS, Proxy, a
B2BUA, registrar and redirect server. Note that a B2BUA is a
degenerate case of a proxy and as such the SIP CLF field layout
format prescribed for a proxy is equally applicable to the B2BUA.
Similarly, registrars and redirect servers are a degenerate case of a
UAS, and as such the SIP CLF field layout prescribed for a UAS is
equally applicable to registrars and redirect servers.
The following sections specify the individual SIP CLF data model
elements that form a log record for specific instance of a SIP
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entity. We limit our specification to using the minimum data model
elements. It is understood that a SIP CLF record is extensible using
extension mechanisms appropriate to the specific representation used
to generate the SIP CLF record. This document, however, does not
prescribe a specific representation format and it limits the
discussion to the mandatory data elements described above.
8.1. SIP CLF data model elements for an UAC
When an UAC generates a request, the following data model elements
--- in the order specified below --- are used to create a SIP CLF
record that is subsequently logged:
Timestamp CSeq R-URI Destination-IP:port Client-Txn
To From Call-ID
Similarly, when an UAC receives a response, the following data model
elements --- in the order specified below --- are used to create a
SIP CLF record that is subsequently logged:
Timestamp CSeq Source-IP:port Status Client-Txn To
8.2. SIP CLF data model elements for an UAS
When an UAS receives a request, the following data model elements ---
in the order specified below --- are used to create a SIP CLF record
that is subsequently logged:
Timestamp CSeq R-URI Source-IP:port Server-Txn To From
Call-ID
Similarly, when an UAS generates a response, the following data model
elements --- in the order specified below --- are used to create a
SIP CLF record that is subsequently logged:
Timestamp CSeq Destination-IP:port Status Server-Txn
8.3. SIP CLF data model elements for a proxy
When the UAS half of a SIP proxy receives a request, the following
data model elements --- in the order specified below --- are used to
create a SIP CLF record that is subsequently logged:
Timestamp CSeq R-URI Source:port Server-Txn To From
Call-ID
Similarly, when a UAS half of a SIP proxy generates a response, the
following data model elements --- in the order specified below ---
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are used to create a SIP CLF record that is subsequently logged:
Timestamp CSeq Destination:port Status Server-Txn Client-Txn
To
The Client-Txn may be empty (or null) since a downstream branch may
not have been created when the response log record is generated.
Imagine a proxy receiving an INVITE request and generating a "100
Trying" response. At the time the provisional response is generated,
the proxy may not have progressed the INVITE transaction to the point
of creating a client transaction or a downstream destination. Thus,
it is acceptable for these fields to be empty (or null.)
When an UAC-half of a SIP proxy generates a request, the following
data model elements --- in the order specified below --- are used to
create a SIP CLF record that is subsequently logged:
Timestamp CSeq R-URI Destination:port Server-Txn
Client-Txn To From Call-ID
Similarly, when an UAC-half receives a response, the following data
model elements --- in the order specified below --- are used to
create a SIP CLF record that is subsequently logged:
Timestamp CSeq Source:port Status Server-Txn Client-Txn To
9. Examples
In the examples below, we use the horizontal dash ("-") to denote
empty (or null) elements. Similarly, the CSeq header field is
represented by Method-Number (e.g., INVITE-32). It is important to
note that the syntax for the examples in this section is for
illustration purposes only, and is not a specific representation of a
logging format. It is expected that one or more documents will
outline specific formats for logging.
The examples use only the mandatory data elements defined in
Section 8. Extension elements are not considered.
There are five principals in the examples below. They are Alice, the
initiator of requests. Alice's user agent uses IPv4 address
198.51.100.1, port 5060. P1 is a proxy that Alice's request traverse
on their way to Bob, the recipient of the requests. P1 also acts as
a registrar to Alice. P1 uses an IPv4 address of 198.51.100.10, port
5060. Bob has two instances of his user agent running on different
hosts. The first instance uses an IPv4 address of 203.0.113.1, port
5060 and the second instance uses an IPv6 address of 2001:db8::9,
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port 5060. P2 is a proxy responsible for Bob's domain. Table 1
summarizes these addresses.
+-------------------+--------------------+-------------------+
| Principal | IP:port | Host/Domain name |
+-------------------+--------------------+-------------------+
| Alice | 198.51.100.1:5060 | alice.example.com |
| P1 | 198.51.100.10:5060 | p1.example.com |
| P2 | 203.0.113.200:5060 | p2.example.net |
| Bob UA instance 1 | 203.0.113.1:5060 | bob1.example.net |
| Bob UA instance 2 | [2001:db8::9]:5060 | bob2.example.net |
+-------------------+--------------------+-------------------+
Principal to IP address asignment
Table 1
Illustrative examples of SIP CLF follow. These examples use the
<allOneLine> tag defined in [RFC4475] to logically denote a single
line.
9.1. UAC registering with a proxy
Alice sends a registration registrar P1 and receives a 2xx-class
response. The register requests causes Alice's UAC to produce a log
record shown below. The mandatory data model elements correspond to
those listed in Section 8.1.
<allOneLine>
1275930743.699 REGISTER-1 sip:example.com 198.51.100.10:5060
ty7u7 sip:example.com sip:alice@example.com;tag=76yhh
f81-d4-f6@example.com
</allOneLine>
After some time, Alice's UAC will receive a response from the
registrar. The response causes Alice's agent to produce a log record
shown below. The mandatory data elements correspond to those listed
in Section 8.1.
<allOneLine>
1275930744.100 REGISTER-1 198.51.100.10:5060 200 ty7u7
sip:example.com;tag=reg-98j
<allOneLine>
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9.2. Direct call between Alice and Bob
In this example, Alice sends a session initiation request directly to
Bob's agent (instance 1.) Bob's agent accepts the session
invitation. We first present the SIP CLF logging from Alice's UAC
point of view. In line 1, Alice's user agent sends out the INVITE.
Shortly, it receives a "180 Ringing" (line 2), followed by a "200 OK"
response (line 3). Upon the receipt of the 2xx-class response,
Alice's user agent sends out an ACK request (line 4).
<allOneLine>
1275930743.699 INVITE-32 sip:bob@bob1.example.net
203.0.113.1:5060 c-1-xt6 sip:bob@example.net
sip:alice@example.com;tag=76yhh f82-d4-f7@example.com
</allOneLine>
<allOneLine>
1275930745.002 INVITE-32 203.0.113.1:5060 180 c-1-xt6
sip:bob@example.net;tag=b-in6-iu
<allOneLine>
<allOneLine>
1275930746.100 INVITE-32 203.0.113.1:5060 200 c-1-xt6
sip:bob@example.net;tag=b-in6-iu
<allOneLine>
<allOneLine>
1275930746.120 ACK-32 sip:bob@bob1.example.net
203.0.113.1:5060 c-1-xt6 sip:bob@example.net;tag=b-in6-iu
sip:alice@example.com;tag=76yhh f82-d4-f7@example.com
<allOneLine>
9.3. Single downstream branch call
In this example, Alice sends a session invitation request to Bob
through proxy P1, which inserts a Record-Route header causing
subsequent requests between Alice and Bob to traverse the proxy. The
SIP CLF log records correspond to the viewpoint of P1. The log
records are presented one per logical line and the line numbers refer
to Figure 1
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Alice P1 Bob
+---INV--------->| | Line 1
| | |
|<---------100---+ | Line 2
| | |
| +---INV-------->| Line 3
| | |
| |<--------100---+ Line 4
| | |
| |<--------180---+ Line 5
| | |
|<---------180---+ | Line 6
| | |
| |<--------200---+ Line 7
| | |
|<---------200---+ | Line 8
| | |
+---ACK--------->| | Line 9
| | |
| |---ACK-------->| Line 10
Figure 1: Simple proxy-aided call flow
<allOneLine>
1 1275930743.699 INVITE-43 sip:bob@example.net
198.51.100.1:5060 s-1-tr sip:bob@example.net
sip:alice@example.com;tag=al-1 tr-87h@example.com
</allOneLine>
<allOneLine>
2 1275930744.001 INVITE-43 198.51.100.1:5060 100 s-1-tr -
sip:bob@example.net
</allOneLine>
<allOneLine>
3 1275930744.998 INVITE-43 sip:bob@bob1.example.net
203.0.113.1:5060 s-1-tr c-1-tr sip:bob@example.net
sip:alice@example.com;tag=a1-1 tr-87h@example.com
</allOneLine>
<allOneLine>
4 1275930745.200 INVITE-43 203.0.113.1:5060 100 s-1-tr c-1-tr
sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
5 1275930745.800 INVITE-43 203.0.113.1:5060 180 s-1-tr c-1-tr
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sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
6 1275930746.009 INVITE-43 198.51.100.1:5060 180 s-1-tr c-1-tr
sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
7 1275930747.120 INVITE-43 203.0.113.1:5060 200 s-1-tr c-1-tr
sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
8 1275930747.300 INVITE-43 198.51.100.1:5060 200 s-1-tr c-1-tr
sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
9 1275930748.201 ACK-43 sip:bob@bob1.example.net
198.51.100.1:5060 s-1-tr sip:bob@example.net;tag=b1-1
sip:alice@example.com;tag=al-1 tr-87h@example.com
</allOneLine>
<allOneLine>
10 1275930749.100 ACK-43 sip:bob@bob1.example.net
203.0.113.1:5060 s-1-tr c-1-tr sip:bob@example.net;tag=b1-1
sip:alice@example.com;tag=al-1 tr-87h@example.com
</allOneLine>
9.4. Forked call
In this example, Alice sends a session invitation to Bob's proxy, P2.
P2 forks the session invitation request to two registered endpoints
corresponding to Bob's address-of-record. Both endpoints respond
with provisional responses. Shortly thereafter, one of Bob's user
agent instances accepts the call, causing P2 to send a CANCEL request
to the second user agent. P2 does not Record-Route, therefore the
subsequent ACK request from Alice to Bob's user agent does not
traverse through P2 (and is not shown below.)
Figure 2 depicts the call flow. The SIP CLF log records correspond
to the viewpoint of P2. The log records are presented one per
logical line and the line numbers refer to Figure 2.
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Bob Bob
Alice P2 (Instance 1) (Instance 2)
+---INV--->| | | Line 1
| | | |
|<---100---+ | | Line 2
| | | |
| +---INV--->| | Line 3
| | | |
| +---INV----+-------->| Line 4
| | | |
| |<---100---+ | Line 5
| | | |
| |<---------+---100---+ Line 6
| | | |
| |<---180---+---------+ Line 7
| | | |
|<---180---+ | | Line 8
| | | |
| |<---180---+ | Line 9
| | | |
|<---180---+ | | Line 10
| | | |
| |<---200---+ | Line 11
| | | |
|<---200---+ | | Line 12
| | | |
| +---CANCEL-+-------->| Line 13
| | | |
| |<---------+---487---+ Line 14
| | | |
| +---ACK----+-------->| Line 15
| | | |
| |<---------+---200---+ Line 16
Figure 2: Forked call flow
<allOneLine>
1 1275930743.699 INVITE-43 sip:bob@example.net
198.51.100.1:5060 s-1-tr sip:bob@example.net
sip:alice@example.com;tag=al-1 tr-87h@example.com
</allOneLine>
<allOneLine>
2 1275930744.001 INVITE-43 198.51.100.1:5060 100 s-1-tr -
sip:bob@example.net
</allOneLine>
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<allOneLine>
3 1275930744.998 INVITE-43 sip:bob@bob1.example.net
203.0.113.1:5060 s-1-tr c-1-tr sip:bob@example.net
sip:alice@example.com;tag=a1-1 tr-87h@example.com
</allOneLine>
<allOneLine>
4 1275930745.500 INVITE-43 sip:bob@bob2.example.net
[2001:db8::9]:5060 s-1-tr c-2-tr sip:bob@example.net
sip:alice@example.com;tag=a1-1 tr-87h@example.com
</allOneLine>
<allOneLine>
5 1275930745.800 INVITE-43 203.0.113.1:5060 100 s-1-tr
c-1-tr sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
6 1275930746.100 INVITE-43 [2001:db8::9]:5060 100 s-1-tr
c-2-tr sip:bob@example.net;tag=b1-2
</allOneLine>
<allOneLine>
7 1275930746.700 INVITE-43 [2001:db8::9]:5060 180 s-1-tr
c-2-tr sip:bob@example.net;tag=b1-2
</allOneLine>
<allOneLine>
8 1275930746.990 INVITE-43 198.51.100.1:5060 180 s-1-tr
c-2-tr sip:bob@example.net;tag=b1-2
<allOneLine>
<allOneLine>
9 1275930747.100 INVITE-43 203.0.113.1:5060 180 s-1-tr
c-1-tr sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
10 1275930747.300 INVITE-43 198.51.100.1:5060 180 s-1-tr
c-1-tr sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
11 1275930747.800 INVITE-43 203.0.113.1:5060 200 s-1-tr
c-1-tr sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
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12 1275930748.000 INVITE-43 198.51.100.1:5060 200 s-1-tr
c-1-tr sip:bob@example.net;tag=b1-1
</allOneLine>
<allOneLine>
13 1275930748.201 CANCEL-43 sip:bob@bob2.example.net
[2001:db8::9]:5060 s-1-tr c-2-tr sip:bob@example.net
sip:alice@example.com;tag=a1-1 tr-87h@example.com
</allOneLine>
<allOneLine>
14 1275930748.991 INVITE-43 [2001:db8::9]:5060 487 s-1-tr c-2-tr
sip:bob@example.net;tag=b1-2
</allOneLine>
<allOneLine>
15 1275930749.455 ACK-43 sip:bob@bob2.example.net [2001:db8::9]:5060
s-1-tr c-2-tr sip:bob@example.net;tag=b1-2
sip:alice@example.com;tag=a1-1 tr-87h@example.com
</allOneLine>
<allOneLine>
16 1275930750.001 CANCEL-43 [2001:db8::9]:5060 200 s-1-tr c-2-tr
sip:bob@example.net;tag=b1-2
</allOneLine>
The above SIP CLF log makes it easy to search for specific
transactions or a state of the session. On a Linux/Unix system, a
command of "grep c-1-tr" on the above log will readily yield the
information that an INVITE was sent to sip:bob@bob1.example.com, it
elicited a 100 followed by a 180 and then a 200. The absence of the
ACK request signifies that the ACK was exchanged end-to-end.
A command of "grep c-2-tr" yields a more complex scenario of sending
an INVITE to sip:bob@bob2.example.net, receiving 100 and 180.
However, the log makes it apparent that the request to
sip:bob@bob2.example.net was subsequently CANCEL'ed before a final
response was generated, and that the pending INVITE returned a 487.
The ACK to the final non-2xx response and a 200 to the CANCEL request
complete the exchange on that branch.
10. Security Considerations
A log file by its nature reveals both the state of the entity
producing it and the nature of the information being logged. To the
extent that this state should not be publicly accessible and that the
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information is to be considered private, appropriate file and
directory permissions attached to the log file should be used. The
following threats may be considered for the log file while it is
stored:
o An attacker may gain access to view the log file, or may
surreptitiously make a copy of the log file for later vieweing;
o An attacker may mount a replay attack by modifying existing
records in the log file or inserting new records;
o An attacker may delete parts of --- or indeed, the whole --- file.
It is outside the scope of this document to specify how to protect
the log file while it is stored on disk. However, operators may
consider using common administrative features such as disk encryption
and securing log files [schneier-1]. Operators may also consider
hardening the machine on which the log files are stored by
restricting physical access to the host as well as restricting access
to the files themselves.
In the worst case, public access to the SIP log file provides the
same information that an adversary can gain using network sniffing
tools (assuming that the SIP traffic is in clear text.) If all SIP
traffic on a network segment is encrypted, then as noted above,
special attention must be directed to the file and directory
permissions associated with the log file to preserve privacy such
that only a privileged user can access the contents of the log file.
Transporting SIP CLF files across the network pose special challenges
as well. The following threats may be considered for transferring
log files or while transferring individual log records:
o An attacker may view the records;
o An attacker may modify the records in transit or insert previously
captured records into the stream;
o An attacker may remove records in transit, or may stage a man- in-
the-middle attack to deliver a partially or entirely falsified log
file.
It is also outside the scope of this document to specify protection
methods for log files or log records that are being transferred
between hosts. However, operators may consider using common security
protocols described in [RFC3552] to transfer log files or individual
records. Alternatively, the log file may be transferred through bulk
methods that also guarantees integrity, or at least detects and
alerts to modification attempts.
The SIP CLF represents the minimum fields that lend themselves to
trend analysis and serve as information that may be deemed useful.
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Other formats can be defined that include more headers (and the body)
from Section 8. However, where to draw a judicial line regarding the
inclusion of non-mandatory headers can be challenging. Clearly, the
more information a SIP entity logs, the longer time the logging
process will take, the more disk space the log entry will consume,
and the more potentially sensitive information could be breached.
Therefore, adequate tradeoffs should be taken in account when logging
more fields than the ones recommended in Section 8.
Implementers need to pay particular attention to buffer handling when
reading or writing log files. SIP CLF entries can be unbounded in
length. It would be reasonable for a full dump of a SIP message to
be thousands of octets long. This is of particular importance to CLF
log parsers, as a SIP CLF log writers may add one or more extension
fields to the message to be logged.
11. Operational guidance
SIP CLF log files will take up substantive amount of disk space
depending on traffic volume at a processing entity and the amount of
information being logged. As such, any enterprise using SIP CLF
should establish operational procedures for file rollovers as
appropriate to the needs of the organization.
Listing such operational guidelines in this document is out of scope
for this work.
NOTE: Preliminary volume analysis was presented to the working group
mailing list during the Anaheim IETF (please see
http://www.ietf.org/mail-archive/web/sip-clf/current/msg00123.html
for the analysis.) An open question is whether the working group
thinks that this analysis should be put in this document.
12. IANA Considerations
This document does not require any considerations from IANA.
13. Acknowledgments
Members of the sipping, dispatch, ipfix and syslog working groups
provided invaluable input to the formulation of the draft. These
include Benoit Claise, Spencer Dawkins, John Elwell, David
Harrington, Christer Holmberg, Hadriel Kaplan, Atsushi Kobayashi,
Jiri Kuthan, Scott Lawrence, Chris Lonvick, Simon Perreault, Adam
Roach, Dan Romascanu, Robert Sparks, Brian Trammell, Dale Worley,
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Theo Zourzouvillys and others that we have undoubtedly, but
inadvertently, missed.
Rainer Gerhards, David Harrington, Cullen Jennings and Gonzalo
Salgueiro helped tremendously in discussions related to arriving at
the beginnings of a data model.
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
14.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC4475] Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J.,
and H. Schulzrinne, "Session Initiation Protocol (SIP)
Torture Test Messages", RFC 4475, May 2006.
[rieck2008]
Rieck, K., Wahl, S., Laskov, P., Domschitz, P., and K-R.
Muller, "A Self-learning System for Detection of Anomalous
SIP Messages", Principles, Systems and Applications of IP
Telecommunications Services and Security for Next
Generation Networks (IPTComm), LNCS 5310, pp. 90-106,
2008.
[schneier-1]
Schneier, B. and J. Kelsey, "Secure audit logs to support
computer forensics", ACM Transactions on Information and
System Security (TISSEC), 2(2), pp. 159,176, May 1999.
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Authors' Addresses
Vijay K. Gurbani (editor)
Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane
Naperville, IL 60566
USA
Email: vkg@bell-labs.com
Eric W. Burger (editor)
This space for sale
USA
Email: eburger@standardstrack.com
URI: http://www.standardstrack.com
Tricha Anjali
Illinois Institute of Technology
316 Siegel Hall
Chicago, IL 60616
USA
Email: tricha@ece.iit.edu
Humberto Abdelnur
INRIA
INRIA - Nancy Grant Est
Campus Scientifique
54506, Vandoeuvre-les-Nancy Cedex
France
Email: Humberto.Abdelnur@loria.fr
Olivier Festor
INRIA
INRIA - Nancy Grant Est
Campus Scientifique
54506, Vandoeuvre-les-Nancy Cedex
France
Email: Olivier.Festor@loria.fr
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