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Versions: (draft-zhou-behave-syslog-nat-logging) 00 01 02 03 04 05 06

Internet Engineering Task Force                                  Z. Chen
Internet-Draft                                             China Telecom
Intended status: Standards Track                                 C. Zhou
Expires: August 22, 2013                             Huawei Technologies
                                                                 T. Tsou
                                               Huawei Technologies (USA)
                                                               T. Taylor
                                                     Huawei Technologies
                                                       February 18, 2013


                     Syslog Format for NAT Logging
                draft-ietf-behave-syslog-nat-logging-00

Abstract

   Under some circumstances operators will need to maintain a dynamic
   record of external address and port assignments made by a NAT device
   (e.g.,Carrier Grade NAT (CGN)), and will find it feasible and
   convenient to create such records using SYSLOG (RFC 5424).  The
   present document standardizes a SYSLOG format to meet that recording
   requirement.  It specifies a number of fields that could be a part of
   the log report, leaving it up to operators to select the fields
   needed for their specific circumstances.

   [*** Subject to discussion*** The log format presented here may also
   be used by PCP server implementations to log the mappings they
   implement.]

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 22, 2013.

Copyright Notice




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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  SYSLOG Record Format For NAT Logging  . . . . . . . . . . . . . 4
     2.1.  SYSLOG HEADER Fields  . . . . . . . . . . . . . . . . . . . 4
     2.2.  STRUCTURED-DATA Fields  . . . . . . . . . . . . . . . . . . 5
       2.2.1.  Incoming IP Source Address Parameter  . . . . . . . . . 5
       2.2.2.  Outgoing IP Source Address Parameter  . . . . . . . . . 5
       2.2.3.  Incoming Source Port Parameter  . . . . . . . . . . . . 5
       2.2.4.  Outgoing Source Port Parameter  . . . . . . . . . . . . 5
       2.2.5.  Number of Port Numbers Parameter  . . . . . . . . . . . 5
       2.2.6.  Highest Outgoing Port Number Parameter  . . . . . . . . 5
       2.2.7.  Protocol Parameter  . . . . . . . . . . . . . . . . . . 6
       2.2.8.  Subscriber Identifier Parameter . . . . . . . . . . . . 6
       2.2.9.  NAT Identifier Parameter  . . . . . . . . . . . . . . . 6
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   5.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

















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1.  Introduction

   Operators already need to record the addresses assigned to
   subscribers at any point in time, for operational and regulatory
   reasons.  When operators introduce NAT devices which support address
   sharing (e.g.,Carrier Grade NATs (CGNs)) into their network, both
   addresses and ports on the external side of the NAT devices are
   shared amongst subscribers.  To trace back from an external address
   and port observed at a given point in time to a specific subscriber
   requires additional information: a record of which subscriber was
   assigned that address and port by the NAT.

   Address-port assignment strategies present a tradeoff between the
   efficiency with which available external addresses are used, the cost
   of maintaining a trace back capability, and the need to make port
   assignments unpredictable to counter the threat of session hijacking.
   At one extreme, the operator could make a one-time assignment of an
   external address and a set of ports to each subscriber.  Traceback
   would then be a matter of retrieving configuration information from
   the NAT.  Even in this situation, it is possible that a request for
   legal interception is placed against a specific subscriber, such that
   each session involving that subscriber is recorded.

   At the opposite extreme, a carrier could assign external addresses
   and ports to subscribers on demand, in totally random fashion.  Such
   a strategy is not really practical, both because of the volume of
   records that would be required to support a traceback capability, and
   because the apparent gain in efficiency with which address-port
   combinations would be utilized would be attenuated by the need to
   leave address-port assignments idle for some minimum amount of time
   after last observed use to make sure they weren't still being used.

   Between these extremes, operators may choose to assign specific
   addresses and specific blocks of ports to subscribers when they log
   on to the network, releasing the assignments when they drop off.
   Such a strategy could be desirable in networks with mobile
   subscribers, in particular.  Compared with the fully dynamic
   strategy, this strategy reduces the number of times that assignments
   have to be recorded by orders of magnitude.

   The point just made is that under some circumstances operators need
   to record allocations of external address-port combinations in the
   NAT dynamically, and the volume of information contained in those
   records is manageable.  Various means are available to create such
   records.  This document assumes that for some operators, the most
   convenient mechanism to do so will be event logging using SYSLOG
   [RFC5424], where the SYSLOG records are generated either by the NAT
   itself or by an off-line device.



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   The next section specifies a SYSLOG record format for logging of NAT
   address and port assignments and the format of fields that could be
   used within such a record.  It is up to individual operators to
   choose the fields that match their specific operating procedures.

1.1.  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 "Key words for use in
   RFCs to Indicate Requirement Levels" [RFC2119].


2.  SYSLOG Record Format For NAT Logging

   This section describes the SYSLOG record format for NAT logging in
   terms of the field names used in [RFC5424] and specified in Section 6
   of that document.  In particular, this section specifies values for
   the APP-NAME and MSGID fields in the record header, the SD-ID
   identifying the STRUCTURED-DATA section, and the PARAM-NAMEs and
   PARAM-VALUE types for the individual possible parameters within that
   section.

2.1.  SYSLOG HEADER Fields

   Within the HEADER portion of the SYSLOG record, the priority (PRI)
   level is subject to local policy, but a default value of 86 is
   suggested, representing a Facility value of 10 (security/
   authorization) and a Severity level of 6 (informational).  Depending
   on where the SYSLOG record is generated, the HOSTNAME field may
   identify the NAT or an offline logging device.  In the latter case,
   it may be desirable to identify the NAT using the NID field in the
   STRUCTURED-DATA section (see below).  The value of the HOSTNAME field
   is subject to the preferences given in Section 6.2.4 of [RFC5424].

   The values of the APP-NAME and MSGID fields in the record header
   determine the semantics of the record.  The RECOMMENDED APP-NAME
   value "NAT" indicates that the record relates to an assignment made
   autonomously by the NAT itself. [*** Subject to discussion*** The
   RECOMMENDED APP-NAME "PCP" indicates that the assignment to which the
   record refers was the result of a Port Control Protocol (PCP)
   [I-D.PCP-Base] command.]  The RECOMMENDED MSGID value "ADD" indicates
   that the assignment took effect at the time indicated by the record
   timestamp.  The RECOMMENDED MSGID value "DEL" indicates that the
   assignment was deleted at the time indicated by the record timestamp.






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2.2.  STRUCTURED-DATA Fields

   This document specifies a value of "asgn" (short for "assignment")
   for the SD-ID field identifying the STRUCTURED-DATA section of the
   record.  In addition it specifies the following parameters for use
   within that section.  All of these parameters are OPTIONAL.  All
   values that are IP addresses are written as a text string in dotted-
   decimal form (IPv4) or as recommended by [RFC5952] (IPv6).

2.2.1.  Incoming IP Source Address Parameter

   PARAM-NAME: iSA.  PARAM-VALUE: the incoming IP source address of the
   packet(s) to which the assignment described by this record applies.

2.2.2.  Outgoing IP Source Address Parameter

   PARAM-NAME: oSA.  PARAM-VALUE: the outgoing IP source address of the
   packet(s) to the assignment described by which this record applies.

2.2.3.  Incoming Source Port Parameter

   PARAM-NAME: iSP.  PARAM-VALUE: the incoming IP source port of the
   packet(s) to the assignment described by which this record applies.

2.2.4.  Outgoing Source Port Parameter

   PARAM-NAME: oSP.  PARAM-VALUE: the outgoing IP source port of the
   packet(s) to which the assignment described by this record applies.
   If the record pertains to the assignment of a range of ports, this
   parameter gives the lowest port number in the range.  In the case of
   a range, either parameter oSPct or parameter oSPmx SHOULD also be
   present in the log record.

2.2.5.  Number of Port Numbers Parameter

   PARAM-NAME: oSPct.  PARAM-VALUE: used when the record pertains to the
   assignment of a range of ports (either consecutive or generated by a
   known algorithm).  This parameter gives the number of port numbers in
   the range.

2.2.6.  Highest Outgoing Port Number Parameter

   PARAM-NAME: oSPmx.  PARAM-VALUE: used when the record pertains to the
   assignment of a range of ports (either consecutive or generated by a
   known algorithm).  This parameter gives the highest port number in
   the range.





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2.2.7.  Protocol Parameter

   PARAM-NAME: Pr.  PARAM-VALUE: an integer indicating the value of the
   Protocol header field (IPv4) or Next Header field (IPv6) in the
   incoming packet(s) to which the assignment described by this record
   applies.

2.2.8.  Subscriber Identifier Parameter

   PARAM-NAME: SID.  PARAM-VALUE: an arbitrary UTF-8 string identifying
   the subscriber to which this assignment applies.  This is intended to
   provide flexibility when the incoming source address will not be
   unique.  The value could be a tunnel identifier, layer 2 address, or
   any other value that is convenient to the operator and associated
   with incoming packets.

2.2.9.  NAT Identifier Parameter

   PARAM-NAME: NID.  PARAM-VALUE: an arbitrary UTF-8 string identifying
   the NAT making the assignment to which this record applies.  Needed
   only if the necessary identification is not provided by the HOSTNAME
   parameter in the log record header.


3.  IANA Considerations

   This document requests IANA to make the following assignments to the
   SYSLOG Structured Data ID Values registry.  RFCxxxx refers to the
   present document when approved.

   +----------------+--------------------+-----------------+-----------+
   | Structured     | Structured Data    | Required or     | Reference |
   | Data ID        | Parameter          | Optional        |           |
   +----------------+--------------------+-----------------+-----------+
   | asgn           |                    | OPTIONAL        | RFCxxxx   |
   |                | iSA                | OPTIONAL        | RFCxxxx   |
   |                | oSA                | OPTIONAL        | RFCxxxx   |
   |                | iSP                | OPTIONAL        | RFCxxxx   |
   |                | oSP                | OPTIONAL        | RFCxxxx   |
   |                | oSPct              | OPTIONAL        | RFCxxxx   |
   |                | oSPmx              | OPTIONAL        | RFCxxxx   |
   |                | Pr                 | OPTIONAL        | RFCxxxx   |
   |                | SID                | OPTIONAL        | RFCxxxx   |
   |                | NID                | OPTIONAL        | RFCxxxx   |
   +----------------+--------------------+-----------------+-----------+

                                  Table 1




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4.  Security Considerations

   When logs are being recorded for regulatory reasons, preservation of
   their integrity and authentication of their origin is essential.  To
   achieve this result, it is RECOMMENDED that the operator deploy
   [RFC5848].

   Access to the logs defined here while the reported assignments are in
   force could improve an attacker's chance of hijacking a session
   through port-guessing.  Even after an assignment has expired, the
   information in the logs SHOULD be treated as confidential, since, if
   revealed, it could help an attacker trace sessions back to a
   particular subscriber or subscriber location.  It is therefore
   RECOMMENDED that these logs be transported securely, using [RFC5425],
   for example, and that they be stored securely at the collector.


5.  Normative References

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

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.

   [RFC5425]  Miao, F., Ma, Y., and J. Salowey, "Transport Layer
              Security (TLS) Transport Mapping for Syslog", RFC 5425,
              March 2009.

   [RFC5848]  Kelsey, J., Callas, J., and A. Clemm, "Signed Syslog
              Messages", RFC 5848, May 2010.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 2010.


Authors' Addresses

   Zhonghua Chen
   China Telecom
   P.R. China

   Phone:
   Email: 18918588897@189.cn








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   Cathy Zhou
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Phone:
   Email: cathy.zhou@huawei.com


   Tina Tsou
   Huawei Technologies (USA)
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

   Phone: +1 408 330 4424
   Email: tina.tsou.zouting@huawei.com


   T. Taylor
   Huawei Technologies
   Ottawa,
   Canada

   Phone:
   Email: tom.taylor.stds@gmail.com
























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