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IPFIX Information Elements for logging NAT Events
draft-ietf-behave-ipfix-nat-logging-04

The information below is for an old version of the document.
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This is an older version of an Internet-Draft that was ultimately published as RFC 8158.
Authors Senthil Sivakumar , Reinaldo Penno
Last updated 2015-10-14 (Latest revision 2014-07-02)
Replaces draft-sivakumar-behave-nat-logging
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draft-ietf-behave-ipfix-nat-logging-04
Behave                                                      S. Sivakumar
Internet-Draft                                                  R. Penno
Intended status: Standards Track                           Cisco Systems
Expires: January 3, 2015                                    July 2, 2014

           IPFIX Information Elements for logging NAT Events
                 draft-ietf-behave-ipfix-nat-logging-04

Abstract

   Network operators expect NAT devices to log events like creation and
   deletion of translations and information about the resources it is
   managing.  The logs are essential in many cases to identify an
   attacker or a host that was used to launch malicious attacks and/or
   for various other purposes of accounting.  Since there is no standard
   way of logging this information, different NAT devices log the
   information using proprietary formats and hence it is difficult to
   expect a consistent behavior.  The lack of a consistent way to log
   the data makes it difficult to write the collector applications that
   would receive this data and process it to present useful information.
   This document describes the formats for logging of NAT events.

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 January 3, 2015.

Copyright Notice

   Copyright (c) 2014 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

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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Event based logging . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Logging of destination information  . . . . . . . . . . .   5
     5.2.  Information Elements  . . . . . . . . . . . . . . . . . .   5
     5.3.  Definition of NAT Events  . . . . . . . . . . . . . . . .   8
     5.4.  Quota exceeded Event types  . . . . . . . . . . . . . . .   9
     5.5.  Threshold reached Event types . . . . . . . . . . . . . .   9
     5.6.  Templates for NAT Events  . . . . . . . . . . . . . . . .  10
       5.6.1.  NAT44 create and delete session events  . . . . . . .  10
       5.6.2.  NAT64 create and delete session events  . . . . . . .  11
       5.6.3.  NAT44 BIB create and delete events  . . . . . . . . .  12
       5.6.4.  NAT64 BIB create and delete events  . . . . . . . . .  12
       5.6.5.  Addresses Exhausted event . . . . . . . . . . . . . .  13
       5.6.6.  Ports Exhausted event . . . . . . . . . . . . . . . .  13
       5.6.7.  Quota exceeded events . . . . . . . . . . . . . . . .  14
         5.6.7.1.  Maximum session entries exceeded  . . . . . . . .  14
         5.6.7.2.  Maximum BIB entries exceeded  . . . . . . . . . .  14
         5.6.7.3.  Maximum entries per user exceeded . . . . . . . .  14
         5.6.7.4.  Maximum active host or subscribers exceeded . . .  15
         5.6.7.5.  Maximum fragments pending reassembly exceeded . .  15
       5.6.8.  Threshold reached events  . . . . . . . . . . . . . .  16
         5.6.8.1.  Address pool high or low threshold reached  . . .  16
         5.6.8.2.  Address and port high threshold reached . . . . .  16
         5.6.8.3.  Per-user Address and port high threshold reached   17
         5.6.8.4.  Global Address mapping high threshold reached . .  17
       5.6.9.  Address binding create and delete events  . . . . . .  18
       5.6.10. Port block allocation and de-allocation . . . . . . .  18
   6.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  IPFIX . . . . . . . . . . . . . . . . . . . . . . . . . .  19
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   9.  Management Considerations . . . . . . . . . . . . . . . . . .  21
     9.1.  Ability to collect events from multiple NAT devices . . .  22
     9.2.  Ability to suppress events  . . . . . . . . . . . . . . .  22
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  22

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   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     11.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Terminology

   The usage of the term "NAT device" in this document refer to any
   NAT44 and NAT64 devices.  The usage of the term "collector" refers to
   any device that receives the binary data from a NAT device and
   converts that into meaningful information.  This document uses the
   term "Session" as it is defined in [RFC2663] and the term BIB as it
   is defined in [RFC6146].  The usage of the term Information Element
   (IE) is defined in [RFC7011].

   The IPFIX Information elements that are NAT specific are created with
   NAT terminology.  In order to avoid creating duplicate IE's, IE's
   that are reused if they convey the same meaning.  However, that
   causes confusion in terminology used in NAT specific terms and IPFIX
   IE's.  Any non-IPFIX terminology used to convey NAT events are
   described in this section.

   The document uses the term timestamp for the Information element
   which defines the time when an event is logged, this is the same as
   IPFIX term observationTimeMilliseconds as described in [IPFIX-IANA].
   Since observationTimeMilliseconds is not self explanatory for NAT
   implementors, this document uses the term timeStamp.

2.  Introduction

   The IPFIX Protocol [RFC7011] defines a generic push mechanism for
   exporting information and events.  The IPFIX Information Model
   [IPFIX-IANA] defines a set of standard Information Elements (IEs)
   which can be carried by the IPFIX protocol.  This document details
   the IPFIX Information Elements(IEs) that MUST be logged by a NAT
   device that supports NAT logging using IPFIX.  The document will
   specify the format of the IE's that SHOULD be logged by the NAT
   device and all the optional fields.  The fields specified in this
   document are gleaned from [RFC4787] and [RFC5382].

   Test [3GPP]

   This document and [I-D.behave-syslog-nat-logging] are provided in
   order to standardize the events and parameters to be recorded, using
   IPFIX [RFC7011] and SYSLOG [RFC5424]respectively.

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2.1.  Requirements Language

   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 [RFC2119].

3.  Scope

   This document provides the information model to be used for logging
   the NAT events including Carrier Grade NAT (CGN) events.  This
   document focuses exclusively on the specification of IPFIX IE's.
   [RFC7011] provides guidance on the choices of the transport protocols
   used and their effects.  This document does not provide guidance on
   the transport protocol like TCP, UDP or SCTP that is to be used to
   log NAT events.  The log events SHOULD NOT be lost but the choice of
   the actual transport protocol is beyond the scope of this document.

   The existing IANA IPFIX IEs registry [IPFIX-IANA] already has
   assignments for many NAT logging events.  For convenience, this
   document uses those same IEs.  However, as stated earlier, this
   document is not defining IPFIX or NetFlow v9 as the framework for
   logging.  Rather, the information elements as defined in the IPFIX-
   IANA registry are within the scope of this document.

   This document assumes that the NAT device will use the existing IPFIX
   framework to send the log events to the collector.  This would mean
   that the NAT device will specify the template that it is going to use
   for each of the events.  The templates can be of varying length and
   there could be multiple templates that a NAT device could use to log
   the events.

   The implementation details of the collector application is beyond the
   scope of this document.

   The optimization of logging the NAT events is left to the
   implementation and is beyond the scope of this document.

4.  Applicability

   NAT logging based on IPFIX uses binary encoding and hence is very
   efficient.  IPFIX based logging is recommended for environments where
   a high volume of logging is required, for example, where per-flow
   logging is needed or in case of Carrier Grade NAT.  However, IPFIX
   based logging requires a collector that processes the binary data and
   requires a network management application that converts this binary
   data to a human readable format.

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5.  Event based logging

   An event in a NAT device can be viewed as a state transition as it
   relates to the management of NAT resources.  The creation and
   deletion of NAT sessions and bindings are examples of events as it
   results in the resources (addresses and ports) being allocated or
   freed.  The events can happen either through the processing of data
   packets flowing through the NAT device or through an external entity
   installing policies on the NAT router or as a result of an
   asynchronous event like a timer.  The list of events are provided in
   Section 4.1.  Each of these events SHOULD be logged, unless they are
   administratively prohibited.  A NAT device MAY log these events to
   multiple collectors if redundancy is required.  The network
   administrator will specify the collectors to which the log records
   are to be sent.

   A collector may receive NAT events from multiple CGN devices and MUST
   be able to distinguish between the devices.  Each CGN device should
   have a unique source ID to identify themselves.  The source ID is
   part of the IPFIX template and data exchange.

   Prior to logging any events, the NAT device MUST send the template of
   the record to the collector to advertise the format of the data
   record that it is using to send the events.  The templates can be
   exchanged as frequently as required given the reliability of the
   connection.  There SHOULD be a configurable timer for controlling the
   template refresh.  NAT device SHOULD combine as many events as
   possible in a single packet to effectively utilize the network
   bandwidth.

5.1.  Logging of destination information

   Logging of destination information in a NAT event has been discussed
   in [RFC6302] and [RFC6888].  Logging of destination information
   increases the size of each record and increases the need for storage
   considerably.  It increases the number of log events generated
   because when the same user connects to a different destination, it
   results in a log record per destination address.  Logging of
   destination information also results in the loss of privacy and hence
   should be done with caution.  However, this draft provides the
   necessary fields to log the destination information in cases where
   they should be logged.

5.2.  Information Elements

   The templates could contain a subset of the Information Elements(IEs)
   shown in Table 1 depending upon the event being logged.  For example
   a NAT44 session creation template record will contain,

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   {sourceIPv4Adress, postNATSourceIPv4Address, destinationIpv4Address,
   postNATDestinationIPv4Address, sourceTransportPort,
   postNAPTSourceTransportPort, destinationTransportPort,
   postNAPTDestTransportPort, internalAddressRealm, natEvent, timeStamp}

   An example of the actual event data record is shown below - in a
   readable form

   {192.168.16.1, 201.1.1.100, 207.85.231.104, 207.85.231.104, 14800,
   1024, 80, 80, 0, 1, 09:20:10:789}

   A single NAT device could be exporting multiple templates and the
   collector MUST support receiving multiple templates from the same
   source.

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   The following is the table of all the IE's that a CGN device would
   need to export the events.  The formats of the IE's and the IPFIX IDs
   are listed below.  Some of the IPFIX IE's are not assigned yet, and
   hence the detailed description of these fields are requested in the
   IANA considerations section.

   +----------------------------------+--------+-------+---------------+
   |            Field Name            |   Size |  IANA |  Description  |
   |                                  | (bits) | IPFIX |               |
   |                                  |        |    ID |               |
   +----------------------------------+--------+-------+---------------+
   |            timeStamp             |     64 |   323 |  System Time  |
   |                                  |        |       |    when the   |
   |                                  |        |       |     event     |
   |                                  |        |       |    occured.   |
   |          natInstanceId           |     32 |   TBD |  NAT Instance |
   |                                  |        |       |   Identifier  |
   |              vlanID              |     16 |    58 |   VLAN ID in  |
   |                                  |        |       |    case of    |
   |                                  |        |       |  overlapping  |
   |                                  |        |       |    networks   |
   |           ingressVRFID           |     32 |   234 |   VRF ID in   |
   |                                  |        |       |    case of    |
   |                                  |        |       |  overlapping  |
   |                                  |        |       |    networks   |
   |        sourceIPv4Address         |     32 |     8 |  Source IPv4  |
   |                                  |        |       |    Address    |
   |     postNATSourceIPv4Address     |     32 |   225 |   Translated  |
   |                                  |        |       |  Source IPv4  |
   |                                  |        |       |    Address    |
   |        protocolIdentifier        |      8 |     4 |   Transport   |
   |                                  |        |       |    protocol   |
   |       sourceTransportPort        |     16 |     7 |  Source Port  |
   |   postNAPTsourceTransportPort    |     16 |   227 |   Translated  |
   |                                  |        |       |  Source port  |
   |      destinationIPv4Address      |     32 |    12 |  Destination  |
   |                                  |        |       |  IPv4 Address |
   |  postNATDestinationIPv4Address   |     32 |   226 |   Translated  |
   |                                  |        |       |      IPv4     |
   |                                  |        |       |  destination  |
   |                                  |        |       |    address    |
   |     destinationTransportPort     |     16 |    11 |  Destination  |
   |                                  |        |       |      port     |
   | postNAPTdestinationTransportPort |     16 |   228 |   Translated  |
   |                                  |        |       |  Destination  |
   |                                  |        |       |      port     |
   |        sourceIPv6Address         |     27 |   128 |  Source IPv6  |
   |                                  |        |       |    address    |

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   |      destinationIPv6Address      |    128 |    28 |  Destination  |
   |                                  |        |       |  IPv6 address |
   |     postNATSourceIPv6Address     |    128 |   281 |   Translated  |
   |                                  |        |       |  source IPv6  |
   |                                  |        |       |    addresss   |
   |  postNATDestinationIPv6Address   |    128 |   282 |   Translated  |
   |                                  |        |       |  Destination  |
   |                                  |        |       |  IPv6 address |
   |       internalAddressRealm       |      8 |   TBD |     Source    |
   |                                  |        |       | Address Realm |
   |       externalAddressRealm       |      8 |   TBD |  Destination  |
   |                                  |        |       | Address Realm |
   |             natEvent             |      8 |   230 | Type of Event |
   |          portRangeStart          |     16 |   361 |   Allocated   |
   |                                  |        |       |   port block  |
   |                                  |        |       |     start     |
   |           portRangeEnd           |     16 |   362 |   Allocated   |
   |                                  |        |       |   Port block  |
   |                                  |        |       |      end      |
   |            natPoolID             |     32 |   283 |    NAT pool   |
   |                                  |        |       |   Identifier  |
   |          natLimitEvent           |     32 |   TBD |  Limit event  |
   |                                  |        |       |   identifier  |
   |        natThresholdEvent         |     32 |   TBD |   Threshold   |
   |                                  |        |       |     event     |
   |                                  |        |       |   identifier  |
   +----------------------------------+--------+-------+---------------+

                      Table 1: Template format Table

5.3.  Definition of NAT Events

   The following are the list of NAT events and the proposed event
   values.  The list can be expanded in the future as necessary.  The
   data record will have the corresponding natEvent value to identify
   the event that is being logged.

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                   +--------------------------+--------+
                   |        Event Name        | Values |
                   +--------------------------+--------+
                   |   NAT44 Session create   |      1 |
                   |   NAT44 Session delete   |      2 |
                   | NAT Addresses exhausted  |      3 |
                   |   NAT64 Session create   |      4 |
                   |   NAT64 Session delete   |      5 |
                   |     NAT44 BIB create     |      6 |
                   |     NAT44 BIB delete     |      7 |
                   |     NAT64 BIB create     |      8 |
                   |     NAT64 BIB delete     |      9 |
                   |   NAT ports exhausted    |     10 |
                   |      Quota exceeded      |     11 |
                   |  Address binding create  |     12 |
                   |  Address binding delete  |     13 |
                   |  Port block allocation   |     14 |
                   | Port block de-allocation |     15 |
                   |    Threshold reached     |     16 |
                   +--------------------------+--------+

                        Table 2: NAT Event ID table

5.4.  Quota exceeded Event types

   The following table shows the sub event types for the Quota exceeded
   or limits reached event.  The events that can be reported are the
   Maximum session entries limit reached, Maximum BIB entries limit
   reached, Maximum session/BIB entries per user limit reached and
   maximum subscribers or hosts limit reached.

            +---------------------------------------+--------+
            |       Quota Exceeded Event Name       | Values |
            +---------------------------------------+--------+
            |        Maximum Session entries        |      1 |
            |          Maximum BIB entries          |      2 |
            |        Maximum entries per user       |      3 |
            |  Maximum active hosts or subscribers  |      4 |
            |  Maximum fragments pending reassembly |      5 |
            +---------------------------------------+--------+

                    Table 3: Quota Exceeded event table

5.5.  Threshold reached Event types

   The following table shows the sub event types for the threshold
   reached event.  The administrator can configure the thresholds and

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   whenever the threshold is reached or exceeded, the corresponding
   events are generated.

   The address pool high threshold event will be reported when the
   address pool reaches a high water mark as defined by the operator.
   This will sever as an indication that the operator might have to add
   more addresses to the pool or an indication that the subsequent users
   may be denied NAT translation mappings.

   The address and port mapping high threshold event is generated, when
   the number of ports in the configured address pool has reached a
   configured threshold.

   The per-user address and port mapping high threshold is generated
   when a single user uses more address and port mapping than a
   configured threshold.

   +---------------------------------------------------------+--------+
   |              Threshold Exceeded Event Name              | Values |
   +---------------------------------------------------------+--------+
   |            Address pool high threshold event            |      1 |
   |             Address pool low threshold event            |      2 |
   |      Address and port mapping high threshold event      |      3 |
   |  Address and port mapping per user high threshold event |      4 |
   |       Global Address mapping high threshold event       |      5 |
   +---------------------------------------------------------+--------+

                      Table 4: Threshold event table

5.6.  Templates for NAT Events

   The following is the template of events that will be logged.  The
   events below are identified at the time of this writing but the set
   of events is extensible.  Depending on the implementation and
   configuration various IE's specified can be included or ignored.

5.6.1.  NAT44 create and delete session events

   These events will be generated when a NAT44 session is created or
   deleted.  The template will be the same, the natEvent will indicate
   whether it is a create or a delete event.  The following is a
   template of the event.

   The destination address and port information is optional as required
   by [RFC6888].  However, when the destination information is
   suppressed, the session log event contains the same information as
   the BIB event.  In such cases, the NAT device SHOULD NOT send both
   BIB and session events.

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      +----------------------------------+-------------+-----------+
      |            Field Name            | Size (bits) | Mandatory |
      +----------------------------------+-------------+-----------+
      |            timeStamp             |          64 |    Yes    |
      |          natInstanceID           |          32 |     No    |
      |       vlanID/ingressVRFID        |          32 |     No    |
      |        sourceIPv4Address         |          32 |    Yes    |
      |     postNATSourceIPv4Address     |          32 |    Yes    |
      |        protocolIdentifier        |           8 |    Yes    |
      |       sourceTransportPort        |          16 |    Yes    |
      |   postNAPTsourceTransportPort    |          16 |    Yes    |
      |      destinationIPv4Address      |          32 |     No    |
      |  postNATDestinationIPv4Address   |          32 |     No    |
      |     destinationTransportPort     |          16 |     No    |
      | postNAPTdestinationTransportPort |          16 |     No    |
      |       internalAddressRealm       |           8 |     No    |
      |       externalAddressRealm       |           8 |     No    |
      |             natEvent             |           8 |    Yes    |
      +----------------------------------+-------------+-----------+

               Table 5: NAT44 Session delete/create template

5.6.2.  NAT64 create and delete session events

   These events will be generated when a NAT64 session is created or
   deleted.  The following is a template of the event.

      +----------------------------------+-------------+-----------+
      |            Field Name            | Size (bits) | Mandatory |
      +----------------------------------+-------------+-----------+
      |            timeStamp             |          64 |    Yes    |
      |          natInstanceID           |          32 |     No    |
      |       vlanID/ingressVRFID        |          32 |     No    |
      |        sourceIPv6Address         |         128 |    Yes    |
      |     postNATSourceIPv4Address     |          32 |    Yes    |
      |        protocolIdentifier        |           8 |    Yes    |
      |       sourceTransportPort        |          16 |    Yes    |
      |   postNAPTsourceTransportPort    |          16 |    Yes    |
      |      destinationIPv6Address      |         128 |     No    |
      |  postNATDestinationIPv4Address   |          32 |     No    |
      |     destinationTransportPort     |          16 |     No    |
      | postNAPTdestinationTransportPort |          16 |     No    |
      |       internalAddressRealm       |           8 |     No    |
      |       externalAddressRealm       |           8 |     No    |
      |             natEvent             |           8 |    Yes    |
      +----------------------------------+-------------+-----------+

            Table 6: NAT64 session create/delete event template

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5.6.3.  NAT44 BIB create and delete events

   These events will be generated when a NAT44 Bind entry is created or
   deleted.  The following is a template of the event.

         +-----------------------------+-------------+-----------+
         |          Field Name         | Size (bits) | Mandatory |
         +-----------------------------+-------------+-----------+
         |          timeStamp          |          64 |    Yes    |
         |        natInstanceID        |          32 |     No    |
         |     vlanID/ingressVRFID     |          32 |     No    |
         |      sourceIPv4Address      |          32 |    Yes    |
         |   postNATSourceIPv4Address  |          32 |    Yes    |
         |      protocolIdentifier     |           8 |     No    |
         |     sourceTransportPort     |          16 |     No    |
         | postNAPTsourceTransportPort |          16 |     No    |
         |     internalAddressRealm    |           8 |     No    |
         |     externalAddressRealm    |           8 |     No    |
         |           natEvent          |           8 |    Yes    |
         +-----------------------------+-------------+-----------+

              Table 7: NAT44 BIB create/delete event template

5.6.4.  NAT64 BIB create and delete events

   These events will be generated when a NAT64 Bind entry is created or
   deleted.  The following is a template of the event.

         +-----------------------------+-------------+-----------+
         |          Field Name         | Size (bits) | Mandatory |
         +-----------------------------+-------------+-----------+
         |          timeStamp          |          64 |    Yes    |
         |        natInstanceID        |          32 |     No    |
         |     vlanID/ingressVRFID     |          32 |     No    |
         |      sourceIPv6Address      |         128 |    Yes    |
         |   postNATSourceIPv4Address  |          32 |    Yes    |
         |      protocolIdentifier     |           8 |     No    |
         |     sourceTransportPort     |          16 |     No    |
         | postNAPTsourceTransportPort |          16 |     No    |
         |     internalAddressRealm    |           8 |     No    |
         |     externalAddressRealm    |           8 |     No    |
         |           natEvent          |           8 |    Yes    |
         +-----------------------------+-------------+-----------+

              Table 8: NAT64 BIB create/delete event template

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5.6.5.  Addresses Exhausted event

   This event will be generated when a NAT device runs out of global
   IPv4 addresses in a given pool of addresses.  Typically, this event
   would mean that the NAT device won't be able to create any new
   translations until some addresses/ports are freed.  This event SHOULD
   be rate limited as many packets hitting the device at the same time
   will trigger a burst of addresses exhausted events.

   The following is a template of the event.  Note that either the NAT
   pool name or the nat pool identifier SHOULD be logged, but not both.

                +---------------+-------------+-----------+
                |   Field Name  | Size (bits) | Mandatory |
                +---------------+-------------+-----------+
                |   timeStamp   |          64 |    Yes    |
                | natInstanceID |          32 |     No    |
                |    natEvent   |           8 |    Yes    |
                |   natPoolID   |          32 |    Yes    |
                +---------------+-------------+-----------+

                 Table 9: Address Exhausted event template

5.6.6.  Ports Exhausted event

   This event will be generated when a NAT device runs out of ports for
   a global IPv4 address.  Port exhaustion shall be reported per
   protocol (UDP, TCP etc).  This event SHOULD be rate limited as many
   packets hitting the device at the same time will trigger a burst of
   port exhausted events.

   The following is a template of the event.

          +--------------------------+-------------+-----------+
          |        Field Name        | Size (bits) | Mandatory |
          +--------------------------+-------------+-----------+
          |        timeStamp         |          64 |    Yes    |
          |      natInstanceID       |          32 |     No    |
          |         natEvent         |           8 |    Yes    |
          | postNATSourceIPv4Address |          32 |    Yes    |
          |    protocolIdentifier    |           8 |    Yes    |
          +--------------------------+-------------+-----------+

                 Table 10: Ports Exhausted event template

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5.6.7.  Quota exceeded events

   This event will be generated when a NAT device cannot allocate
   resources as a result of an administratively defined policy.  The
   quota exceeded event templates are described below.

5.6.7.1.  Maximum session entries exceeded

   The maximum session entries exceeded is generated when the
   administratively configured limit is reached.  The following is the
   template of the event.

               +-----------------+-------------+-----------+
               |    Field Name   | Size (bits) | Mandatory |
               +-----------------+-------------+-----------+
               |    timeStamp    |          64 |    Yes    |
               |  natInstanceID  |          32 |     No    |
               |     natEvent    |           8 |    Yes    |
               |  natLimitEvent  |          32 |    Yes    |
               | configuredLimit |          32 |    Yes    |
               +-----------------+-------------+-----------+

             Table 11: Session Entries Exceeded event template

5.6.7.2.  Maximum BIB entries exceeded

   The maximum BIB entries exceeded is generated when the
   administratively configured limit is reached.  The following is the
   template of the event.

               +-----------------+-------------+-----------+
               |    Field Name   | Size (bits) | Mandatory |
               +-----------------+-------------+-----------+
               |    timeStamp    |          64 |    Yes    |
               |  natInstanceID  |          32 |     No    |
               |     natEvent    |           8 |    Yes    |
               |  natLimitEvent  |          32 |    Yes    |
               | configuredLimit |          32 |    Yes    |
               +-----------------+-------------+-----------+

               Table 12: BIB Entries Exceeded event template

5.6.7.3.  Maximum entries per user exceeded

   This event is generated when a single user reaches the
   administratively configured limit.  The following is the template of
   the event.

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           +---------------------+-------------+---------------+
           |      Field Name     | Size (bits) |   Mandatory   |
           +---------------------+-------------+---------------+
           |      timeStamp      |          64 |      Yes      |
           |    natInstanceID    |          32 |       No      |
           |       natEvent      |           8 |      Yes      |
           |    natLimitEvent    |          32 |      Yes      |
           |   configuredLimit   |          32 |      Yes      |
           | vlanID/ingressVRFID |          32 |       No      |
           |  sourceIPv4 address |          32 | Yes for NAT44 |
           |  sourceIPv6 address |         128 | Yes for NAT64 |
           +---------------------+-------------+---------------+

            Table 13: Per-user Entries Exceeded event template

5.6.7.4.  Maximum active host or subscribers exceeded

   This event is generated when the number of allowed hosts or
   subscribers reaches the administratively configured limit.  The
   following is the template of the event.

               +-----------------+-------------+-----------+
               |    Field Name   | Size (bits) | Mandatory |
               +-----------------+-------------+-----------+
               |    timeStamp    |          64 |    Yes    |
               |  natInstanceID  |          32 |     No    |
               |     natEvent    |           8 |    Yes    |
               |  natLimitEvent  |          32 |    Yes    |
               | configuredLimit |          32 |    Yes    |
               +-----------------+-------------+-----------+

        Table 14: Maximum hosts/subscribers Exceeded event template

5.6.7.5.  Maximum fragments pending reassembly exceeded

   This event is generated when the number of fragments pending
   reassembly reaches the administratively configured limit.  The
   following is the template of the event.

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          +----------------------+-------------+---------------+
          |      Field Name      | Size (bits) |   Mandatory   |
          +----------------------+-------------+---------------+
          |      timeStamp       |          64 |      Yes      |
          |    natInstanceID     |          32 |       No      |
          |       natEvent       |           8 |      Yes      |
          |    natLimitEvent     |          32 |      Yes      |
          |   configuredLimit    |          32 |      Yes      |
          | internalAddressRealm |           8 |      Yes      |
          | vlanID/ingressVRFID  |          32 |       No      |
          |  sourceIPv4 address  |          32 | Yes for NAT44 |
          |  sourceIPv6 address  |         128 | Yes for NAT64 |
          +----------------------+-------------+---------------+

       Table 15: Maximum fragments pending reassembly Exceeded event
                                 template

5.6.8.  Threshold reached events

   This event will be generated when a NAT device reaches a operator
   configured threshold when allocating resources.  The threshold
   reached events are described in the section above.  The following is
   a template of the individual events.

5.6.8.1.  Address pool high or low threshold reached

   This event is generated when the high or low threshold is reached for
   the address pool.  The template is the same for both high and low
   threshold events

              +-------------------+-------------+-----------+
              |     Field Name    | Size (bits) | Mandatory |
              +-------------------+-------------+-----------+
              |     timeStamp     |          64 |    Yes    |
              |   natInstanceID   |          32 |     No    |
              |      natEvent     |           8 |    Yes    |
              | natThresholdEvent |          32 |    Yes    |
              |     natPoolID     |          32 |    Yes    |
              |  configuredLimit  |          32 |    Yes    |
              +-------------------+-------------+-----------+

     Table 16: Address pool high/low threshold reached event template

5.6.8.2.  Address and port high threshold reached

   This event is generated when the high threshold is reached for the
   address pool and ports.

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              +-------------------+-------------+-----------+
              |     Field Name    | Size (bits) | Mandatory |
              +-------------------+-------------+-----------+
              |     timeStamp     |          64 |    Yes    |
              |   natInstanceID   |          32 |     No    |
              |      natEvent     |           8 |    Yes    |
              | natThresholdEvent |          32 |    Yes    |
              |  configuredLimit  |          32 |    Yes    |
              +-------------------+-------------+-----------+

       Table 17: Address port high threshold reached event template

5.6.8.3.  Per-user Address and port high threshold reached

   This event is generated when the high threshold is reached for the
   per-user address pool and ports.

           +---------------------+-------------+---------------+
           |      Field Name     | Size (bits) |   Mandatory   |
           +---------------------+-------------+---------------+
           |      timeStamp      |          64 |      Yes      |
           |    natInstanceID    |          32 |       No      |
           |       natEvent      |           8 |      Yes      |
           |  natThresholdEvent  |          32 |      Yes      |
           |   configuredLimit   |          32 |      Yes      |
           | vlanID/ingressVRFID |          32 |       No      |
           |  sourceIPv4 address |          32 | Yes for NAT44 |
           |  sourceIPv6 address |         128 | Yes for NAT64 |
           +---------------------+-------------+---------------+

   Table 18: Per-user Address port high threshold reached event template

5.6.8.4.  Global Address mapping high threshold reached

   This event is generated when the high is reached for the per-user
   address pool and ports.  This is generated only by NAT devices that
   use a address pooling behavior of paired.

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             +---------------------+-------------+-----------+
             |      Field Name     | Size (bits) | Mandatory |
             +---------------------+-------------+-----------+
             |      timeStamp      |          64 |    Yes    |
             |    natInstanceID    |          32 |     No    |
             |       natEvent      |           8 |    Yes    |
             |  natThresholdEvent  |          32 |    Yes    |
             |   configuredLimit   |          32 |    Yes    |
             | vlanID/ingressVRFID |          32 |     No    |
             +---------------------+-------------+-----------+

       Table 19: Global Address mapping high threshold reached event
                                 template

5.6.9.  Address binding create and delete events

   These events will be generated when a NAT device binds a local
   address with a global address and when the global address is freed.
   This binding event happens when the first packet of the first flow
   from a host in the private realm.

     +--------------------------------+-------------+---------------+
     |           Field Name           | Size (bits) |   Mandatory   |
     +--------------------------------+-------------+---------------+
     |           timeStamp            |          64 |      Yes      |
     |         natInstanceID          |          32 |       No      |
     |            natEvent            |           8 |      Yes      |
     |       sourceIPv4 address       |          32 | Yes for NAT44 |
     |       sourceIPv6 address       |         128 | Yes for NAT64 |
     | Translated Source IPv4 Address |          32 |      Yes      |
     +--------------------------------+-------------+---------------+

                  Table 20: NAT Address Binding template

5.6.10.  Port block allocation and de-allocation

   This event will be generated when a NAT device allocates/de-allocates
   ports in a bulk fashion, as opposed to allocating a port on a per
   flow basis.

   portRangeStart represents the starting value of the range.

   portRangeEnd represents the ending value of the range.

   NAT devices would do this in order to reduce logs and potentially to
   limit the number of connections a subscriber is allowed to use.  In
   the following Port Block allocation template, the portRangeStart and
   portRangeEnd MUST be specified.

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   It is up to the implementation to choose to consolidate log records
   in case two consecutive port ranges for the same user are allocated
   or freed.

     +--------------------------------+-------------+---------------+
     |           Field Name           | Size (bits) |   Mandatory   |
     +--------------------------------+-------------+---------------+
     |           timeStamp            |          64 |      Yes      |
     |         natInstanceID          |          32 |       No      |
     |            natEvent            |           8 |      Yes      |
     |       sourceIPv4 address       |          32 | Yes for NAT44 |
     |       sourceIPv6 address       |         128 | Yes for NAT64 |
     | Translated Source IPv4 Address |          32 |      Yes      |
     |         portRangeStart         |          16 |      Yes      |
     |          portRangeEnd          |          16 |       No      |
     +--------------------------------+-------------+---------------+

            Table 21: NAT Port Block Allocation event template

6.  Encoding

6.1.  IPFIX

   This document uses IPFIX as the encoding mechanism to describe the
   logging of NAT events.  However, the information that is logged
   SHOULD be the same irrespective of what kind of encoding scheme is
   used.  IPFIX is chosen because is it an IETF standard that meets all
   the needs for a reliable logging mechanism.  IPFIX provides the
   flexibility to the logging device to define the data sets that it is
   logging.  The IEs specified for logging MUST be the same irrespective
   of the encoding mechanism used.

7.  Acknowledgements

   Thanks to Dan Wing, Selvi Shanmugam, Mohamed Boucadir, Jacni Qin
   Ramji Vaithianathan, Simon Perreault, Jean-Francois Tremblay, Paul
   Aitken, Julia Renouard, Spencer Dawkins and Brian Trammel for their
   review and comments.

8.  IANA Considerations

   The following information elements are requested from IANA IPFIX
   registry.

   Name : natInstanceId

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   Description: This Information Element identifies an Instance of the
   NAT that runs on a NAT middlebox function after the packet passed the
   Observation Point.

   Abstract Data Type: unsigned32

   Data Type Semantics: identifier

   Reference:

   See RFC 791 [RFC791] for the definition of the IPv4 source address
   field.  See RFC 3022 [RFC3022] for the definition of NAT.  See RFC
   3234 [RFC3234] for the definition of middleboxes.

   Name: internalAddressRealm

   Description: This Information Element represents the internal address
   realm where the packet is originated from or destined to.  By
   definition, a NAT mapping can be created from two address realms, one
   from internal and one from external.  Realms are implementation
   dependent and can represent a VRF ID or a VLAN ID or some unique
   identifier.  Realms are optional and when left unspecified would mean
   that the external and internal realms are the same.

   Abstract Data Type: unsigned8

   Data Type Semantics: identifier

   Reference:

   See RFC 791 [RFC791] for the definition of the IPv4 source address
   field.  See RFC 3022 [RFC3022] for the definition of NAT.  See RFC
   3234 [RFC3234] for the definition of middleboxes.

   Name: externalAddressRealm

   Description: This Information Element represents the external address
   realm where the packet is originated from or destined to.  The
   detailed definition is in the internal address realm as specified
   above.

   Abstract Data Type: unsigned8

   Data Type Semantics: identifier

   Reference:

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   See RFC 791 [RFC791] for the definition of the IPv4 source address
   field.  See RFC 3022 [RFC3022] for the definition of NAT.  See RFC
   3234 [RFC3234] for the definition of middleboxes.

   Name : natLimitEvent

   Description: This Information Element identifies the limit type that
   is reported by the event.  There are different types of limits as
   describer in Table 3.

   Abstract Data Type: unsigned32

   Data Type Semantics: identifier

   Reference:

   See RFC 791 [RFC791] for the definition of the IPv4 source address
   field.  See RFC 3022 [RFC3022] for the definition of NAT.  See RFC
   3234 [RFC3234] for the definition of middleboxes.

   Name: natThresholdEvent

   Description: This Information Element identifies the threshold type
   that is reported by the event.  There are different types of
   thresholds as describer in Table 4.

   Abstract Data Type: unsigned32

   Data Type Semantics: identifier

   Reference:

   See RFC 791 [RFC791] for the definition of the IPv4 source address
   field.  See RFC 3022 [RFC3022] for the definition of NAT.  See RFC
   3234 [RFC3234] for the definition of middleboxes.

9.  Management Considerations

   This section considers requirements for management of the log system
   to support logging of the events described above.  It first covers
   requirements applicable to log management in general.  Any additional
   standardization required to fullfil these requirements is out of
   scope of the present document.  Some management considerations is
   covered in [I-D.behave-syslog-nat-logging].  This document covers the
   additional considerations.

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9.1.  Ability to collect events from multiple NAT devices

   An IPFIX collector MUST be able to collect events from multiple NAT
   devices and be able to decipher events based on the sourceID in the
   IPFIX header.

9.2.  Ability to suppress events

   The exhaustion events can be overwhelming during traffic bursts and
   hence SHOULD be handled by the NAT devices to rate limit them before
   sending them to the collectors.  For eg. when the port exhaustion
   happens during bursty conditions, instead of sending a port
   exhaustion event for every packet, the exhaustion events SHOULD be
   rate limited by the NAT device.

10.  Security Considerations

   None.

11.  References

11.1.  Normative References

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

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations", RFC
              2663, August 1999.

   [RFC4787]  Audet, F. and C. Jennings, "Network Address Translation
              (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
              RFC 4787, January 2007.

   [RFC5382]  Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
              Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
              RFC 5382, October 2008.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6302]  Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
              "Logging Recommendations for Internet-Facing Servers", BCP
              162, RFC 6302, June 2011.

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   [RFC6888]  Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common Requirements for Carrier-Grade NATs
              (CGNs)", BCP 127, RFC 6888, April 2013.

11.2.  Informative References

   [I-D.ietf-behave-syslog-nat-logging]
              Chen, Z., Zhou, C., Tsou, T., and T. Taylor, "Syslog
              Format for NAT Logging", draft-ietf-behave-syslog-nat-
              logging-06 (work in progress), January 2014.

   [IPFIX-IANA]
              IANA, "IPFIX Information Elements registry",
              <http://www.iana.org/assignments/ipfix>.

   [RFC5101bis]
              Claise, B. and B. Trammel, "Specification of the IP Flow
              Information eXport (IPFIX) Protocol for the Exchange of
              Flow Information", July 2013.

   [RFC5102bis]
              Claise, B. and B. Trammel, "Information Model for IP Flow
              Information eXport (IPFIX)", February 2013.

   [RFC5470]  Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
              "Architecture for IP Flow Information Export", RFC 5470,
              March 2009.

   [RFC7011]  Claise, B., Trammell, B., and P. Aitken, "Specification of
              the IP Flow Information Export (IPFIX) Protocol for the
              Exchange of Flow Information", STD 77, RFC 7011, September
              2013.

Authors' Addresses

   Senthil Sivakumar
   Cisco Systems
   7100-8 Kit Creek Road
   Research Triangle Park, North Carolina  27709
   USA

   Phone: +1 919 392 5158
   Email: ssenthil@cisco.com

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   Renaldo Penno
   Cisco Systems
   170 W Tasman Drive
   San Jose, California  95035
   USA

   Email: repenno@cisco.com

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