Behave S. Sivakumar
Internet-Draft R. Penno
Intended status: Standards Track Cisco Systems
Expires: July 13, 2017 January 9, 2017

IPFIX Information Elements for logging NAT Events
draft-ietf-behave-ipfix-nat-logging-13

Abstract

Network operators require NAT devices to log events like creation and deletion of translations and information about the resources that the NAT device is managing. The logs are essential in many cases to identify an attacker or a host that was used to launch malicious attacks and 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 July 13, 2017.

Copyright Notice

Copyright (c) 2017 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

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 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, and all the optional fields. The fields specified in this document are gleaned from [RFC4787] and [RFC5382].

This document and [I-D.ietf-behave-syslog-nat-logging] are written in order to standardize the events and parameters to be recorded, using IPFIX [RFC7011] and SYSLOG [RFC5424]respectively. The intent is to provide a consistent way to log information irrespective of the mechanism that is used.

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.

1.1. 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 Binding Information Base (BIB) as it is defined in [RFC6146]. The usage of the term Information Element (IE) is defined in [RFC7011]. The term Carrier Grade NAT refers to a large scale NAT device as described in [RFC6888]

The IPFIX Information Elements that are NAT specific are created with NAT terminology. In order to avoid creating duplicate IEs, IEs are reused if they convey the same meaning. This 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. This document refers to event templates, that refers to IPFIX template records. This document refers to log events that refers to IPFIX Flow records.

1.2. 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].

2. Scope

This document provides the information model to be used for logging the NAT events including Carrier Grade NAT (CGN) events. [RFC7011] provides guidance on the choices of the transport protocols used for IPFIX 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 logs SHOULD be reliably sent to the collector to ensure that the log events are not lost. 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 most of the NAT logging events. This document uses the allocated IPFIX IEs and will request IANA for the ones that are defined in this document but not yet allocated.

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.

3. Deployment

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.

A collector may receive NAT events from multiple CGN devices. The collector distinguishes between the devices using the source IP address, source port, and Observation Domain ID in the IPFIX header. The collector can decide to store the information based on the administrative policies that are inline with the operator and the local juridiction. The retention policy is not dictated by the exporter and is left to the policies that are defined at the collector.

A collector may have scale issues if it is overloaded by a large number of simultaneous events. An appropriate throttling mechanism may be used to handle the oversubscription.

The logs that are exported can be used for a variety of reasons. An example use case is to do accounting based on when the users logged on and off. The translation will be installed when the user logs on and removed when the user logs off. These events create log records. Another use case is to identify an attacker or a host in a provider network. The network administrators can use these logs to identify the usage patterns, need for additional IP addresses etc. The deployment of NAT logging is not limited to just these cases.

4. 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 they result in resources (addresses and ports) being allocated or freed. The events can happen 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 Table 2. 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. It is necessary to preserve the list of collectors and its associated information like the IPv4/IPv6 address, port and protocol across reboots so that the configuration information is not lost when the device is restarted. The NAT device implementing the IPFIX logging MUST follow the IPFIX specs as specified in RFC 7011.

4.1. 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 the source and destination addresses result in loss of privacy. Logging of destination addresses and ports, pre or post NAT, SHOULD NOT be done [RFC6888]. However, this draft provides the necessary fields to log the destination information in cases where they must be logged.

4.2. Information Elements

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

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

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

{192.0.2.1, 203.0.113.100, 192.0.2.104, 192.0.2.104, 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.


















































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

Template format Table
Field Name Size (bits) IANA IPFIX ID Description
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 128 27 Source IPv6 address
destinationIPv6Address 128 28 Destination IPv6 address
postNATSourceIPv6Address 128 281 Translated source IPv6 addresss
postNATDestinationIPv6Address 128 282 Translated Destination IPv6 address
internalAddressRealm OctetArray TBD Source Address Realm
externalAddressRealm OctetArray 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
natQuotaExceededEvent 32 TBD Limit event identifier
natThresholdEvent 32 TBD Threshold event identifier

4.3. Definition of NAT Events

The following is the complete list of NAT events and the proposed event type values. The natEvent IE is defined in the IPFIX IANA registry in http://www.iana.org/assignments/ipfix/ipfix.xml. The list can be expanded in the future as necessary. The data record will have the corresponding natEvent value to indicate the event that is being logged.

Note that the first two events are marked historic. These values were defined prior to the existence of this draft and outside the IETF working group. These events are not standalone and require more information need to be conveyed to qualify the event. For example, the NAT Translation create event does not specify if it is a NAT44 or NAT64. As a result the Behave WG decided to have explicit definition for each one of the unique events. The historic events are listed here for the purpose of completeness and are already defined in the IPFIX IANA registry. Any compliant implementation SHOULD NOT implement the events that are marked historic.

NAT Event ID table
Event Name Values
NAT Translation create (Historic) 1
NAT Translation Delete (Historic) 2
NAT Addresses exhausted 3
NAT44 Session create 4
NAT44 Session delete 5
NAT64 Session create 6
NAT64 Session delete 7
NAT44 BIB create 8
NAT44 BIB delete 9
NAT64 BIB create 10
NAT64 BIB delete 11
NAT ports exhausted 12
Quota exceeded 13
Address binding create 14
Address binding delete 15
Port block allocation 16
Port block de-allocation 17
Threshold reached 18

4.4. Quota exceeded Event types

The Quota Exceeded event is a natEvent IE described in Table 2. The Quota exceeded events are generated when the hard limits set by the administrator has been reached or exceeded. 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, Maximum active hosts limit reached or maximum subscribers limit reached and Maximum Fragments pending reassembly limit reached.

Quota Exceeded event table
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

4.5. Threshold reached Event types

The following table shows the sub event types for the threshold reached event. The administrator can configure the thresholds and whenever the threshold is reached or exceeded, the corresponding events are generated. The main difference between Quota Exceeded and the Threshold reached events is that, once the Quota exceeded events are hit, the packets are dropped or mappings wont be created etc, whereas, the threshold reached events will provide the operator a chance to take action before the traffic disruptions can happen. A NAT device can choose to implement one or the other or both.

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 serve 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 pool low threshold event will be reported when the address pool reaches a low water mark as defined by the operator. This will serve as an indication that the operator can reclaim some of the global IPv4 addresses in the pool.

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. We don't track the low threshold for per-user address and port mappings, because as the ports are freed, the address will become available. The address pool low threhold event will then be triggered so that the IPv4 global address can be reclaimed.

The Global address mapping high threshold event is generated when the maximum mappings per-user is reached for a NAT device doing paired address pooling.

Threshold event table
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

4.6. 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. A NAT device that implements a given NAT event MUST support the mandatory IE's in the templates. Depending on the implementation and configuration various IEs that are not mandatory can be included or ignored.

4.6.1. 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.

NAT44 Session delete/create template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
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
natInstanceID 32 No
vlanID/ingressVRFID 32 No
internalAddressRealm OctetArray No
externalAddressRealm OctetArray No

4.6.2. 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.

NAT64 session create/delete event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
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
natInstanceID 32 No
vlanID/ingressVRFID 32 No
internalAddressRealm OctetArray No
externalAddressRealm OctetArray No

4.6.3. 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.

NAT44 BIB create/delete event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
sourceIPv4Address 32 Yes
postNATSourceIPv4Address 32 Yes
protocolIdentifier 8 No
sourceTransportPort 16 No
postNAPTsourceTransportPort 16 No
natInstanceID 32 No
vlanID/ingressVRFID 32 No
internalAddressRealm OctetArray No
externalAddressRealm OctetArray No

4.6.4. 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.

NAT64 BIB create/delete event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
sourceIPv6Address 128 Yes
postNATSourceIPv4Address 32 Yes
protocolIdentifier 8 No
sourceTransportPort 16 No
postNAPTsourceTransportPort 16 No
natInstanceID 32 No
vlanID/ingressVRFID 32 No
internalAddressRealm OctetArray No
externalAddressRealm OctetArray No

4.6.5. 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.

Address Exhausted event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natPoolID 32 Yes
natInstanceID 32 No

4.6.6. 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.

Ports Exhausted event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
postNATSourceIPv4Address 32 Yes
protocolIdentifier 8 Yes
natInstanceID 32 No

4.6.7. 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.

4.6.7.1. Maximum session entries exceeded

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

Session Entries Exceeded event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natQuotaExceededEvent 32 Yes
configuredLimit 32 Yes
natInstanceID 32 No

4.6.7.2. Maximum BIB entries exceeded

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

BIB Entries Exceeded event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natQuotaExceededEvent 32 Yes
configuredLimit 32 Yes
natInstanceID 32 No

4.6.7.3. Maximum entries per user exceeded

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

Per-user Entries Exceeded event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natQuotaExceededEvent 32 Yes
configuredLimit 32 Yes
sourceIPv4 address 32 Yes for NAT44
sourceIPv6 address 128 Yes for NAT64
natInstanceID 32 No
vlanID/ingressVRFID 32 No

4.6.7.4. 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.

Maximum hosts/subscribers Exceeded event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natQuotaExceededEvent 32 Yes
configuredLimit 32 Yes
natInstanceID 32 No

4.6.7.5. Maximum fragments pending reassembly exceeded

This event is generated when the number of fragments pending reassembly reaches the administratively configured limit. Note that in case of NAT64, when this condition is detected in the IPv6 to IPv4 direction, the IPv6 source address is mandatory in the template. Similarly, when this condition is detected in IPv4 to IPv6 direction, the source IPv4 address is mandatory in the template below. The following is the template of the event.

Maximum fragments pending reassembly Exceeded event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natQuotaExceededEvent 32 Yes
configuredLimit 32 Yes
sourceIPv4 address 32 Yes for NAT44
sourceIPv6 address 128 Yes for NAT64
natInstanceID 32 No
vlanID/ingressVRFID 32 No
internalAddressRealm OctetArray No

4.6.8. 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.

4.6.8.1. 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

Address pool high/low threshold reached event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natThresholdEvent 32 Yes
natPoolID 32 Yes
configuredLimit 32 Yes
natInstanceID 32 No

4.6.8.2. Address and port high threshold reached

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

Address port high threshold reached event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natThresholdEvent 32 Yes
configuredLimit 32 Yes
natInstanceID 32 No

4.6.8.3. 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.

Per-user Address port high threshold reached event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natThresholdEvent 32 Yes
configuredLimit 32 Yes
sourceIPv4 address 32 Yes for NAT44
sourceIPv6 address 128 Yes for NAT64
natInstanceID 32 No
vlanID/ingressVRFID 32 No

4.6.8.4. Global Address mapping high threshold reached

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

Global Address mapping high threshold reached event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natThresholdEvent 32 Yes
configuredLimit 32 Yes
natInstanceID 32 No
vlanID/ingressVRFID 32 No

4.6.9. 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. A NAT device will generate the binding events when it receives the first packet of the first flow from a host in the private realm.

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

4.6.10. 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.

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.

NAT Port Block Allocation event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
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
natInstanceID 32 No

5. 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 are covered in [I-D.ietf-behave-syslog-nat-logging]. This document covers the additional considerations.

5.1. 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 Observation Domain ID in the IPFIX header.

5.2. 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.

6. 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 Trammell for their review and comments.

7. IANA Considerations

7.1. Information Elements

IANA will register the following IEs in the IPFIX Information Elements registry at http://www.iana.org/assignments/ipfix/ipfix.xml

7.1.1. natInstanceID

Name : natInstanceID

Description: This Information Element uniquely identifies an Instance of the NAT that runs on a NAT middlebox function after the packet passed the Observation Point. natInstanceID is defined in RFC 7659 [RFC7659]

Abstract Data Type: unsigned32

Data Type Semantics: identifier

Reference:

See RFC 791 [RFC0791] 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.

7.1.2. internalAddressRealm

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: octetArray

Data Type Semantics: identifier

Reference:

See RFC 791 [RFC0791] 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.

7.1.3. externalAddressRealm

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: octetArray

Data Type Semantics: identifier

Reference:

See RFC 791 [RFC0791] 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.

7.1.4. natQuotaExceededEvent

Values of this Information Element are defined in a registry maintained by IANA at <http://www.iana.org/assignments/ipfix/ipfix.xml#TBD-by-IANA>. New assignments of values will be administered by IANA, subject to Expert Review [RFC5226]. Experts need to check definitions of new values for completeness, accuracy, and redundancy.

Name : natQuotaExceededEvent

Description: This Information Element identifies the type of a NAT quota exceeded event. Values for this Information Element are listed in the NAT quota exceed event type registry, see [http://www.iana.org/assignments/ipfix/ipfix.xml#TBD-by-IANA] Initial values in the registry are defined by the table below.

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

Abstract Data Type: unsigned32

Data Type Semantics: identifier

Reference:

See RFC 791 [RFC0791] 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.

7.1.5. natThresholdEvent

Values of this Information Element are defined in a registry maintained by IANA at http://www.iana.org/assignments/ipfix/ipfix.xml#TBD-by-IANA. New assignments of values will be administered by IANA, subject to Expert Review [RFC5226]. Experts need to check definitions of new values for completeness, accuracy, and redundancy.

Name: natThresholdEvent

Description: This Information Element identifies a type of a NAT threshold event. Values for this Information Element are listed in the NAT threshhold event type registry, see <http://www.iana.org/assignments/ipfix/ipfix.xml#TBD-by-IANA>. Initial values in the registry are defined by the table below.

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

Abstract Data Type: unsigned32

Data Type Semantics: identifier

Reference:

See RFC 791 [RFC0791] 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.

7.1.6. natEvent

The original definition of this Information Element specified only three values 1, 2, and 3. This definition is replaced by a registry, to which new values can be added. The semantics of the three originally defined values remains unchanged. IANA maintains the registry for values of this Information Element at <http://www.iana.org/assignments/ipfix/ipfix.xml#TBD-by-IANA>. New assignments of values will be administered by IANA, subject to Expert Review [RFC5226]. Experts need to check definitions of new values for completeness, accuracy, and redundancy.

Name : natEvent

Description: Description: This Information Element identifies a NAT event. This IE identifies the type of a NAT event. Examples of NAT events include but not limited to, creation or deletion of a NAT translation entry, a threshold reached or exceeded etc. Values for this Information Element are listed in the NAT event type registry, see [http://www.iana.org/assignments/ipfix/ipfix.xml#TBD-by-IANA] The NAT Event values in the registry are defined by the Table 2 in Section 5.3.

Abstract Data Type: unsigned8

Data Type Semantics: identifier

Element ID : 230

Reference:

See RFC 3022 [RFC3022] for the definition of NAT. See RFC 3234 [RFC3234] for the definition of middleboxes. See [thisRFC] for the definitions of values 4-16.

8. Security Considerations

The security considerations listed in detail for IPFIX in [RFC7011] applies to this draft as well. As described in [RFC7011] the messages exchanged between the NAT device and the collector MUST be protected to provide confidentiality, integrity and authenticity. Without those characteristics, the messages are subject to various kinds of attacks. These attacks are described in great detail in [RFC7011].

This document re-emphasizes the use of TLS or DTLS for exchanging the log messages between the NAT device and the collector. The log events sent in clear text can result in confidential data being exposed to attackers, who could then spoof log events based on the information in clear text messages. Hence, the log events SHOULD NOT be sent in clear text.

The logging of NAT events can result in privacy concerns as result of exporting information such as source address and port information. The logging of destinaion information can also cause privacy concerns but it has been well documented in [RFC6888]. A NAT device can choose to operate in various logging modes if it wants to avoid logging of private information. The collector that receives the information can also choose to mask the private information but generate reports based on abstract data. It is outside the scope of this document to address the implementation of logging modes for privacy considerations.

9. References

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 2007.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S. and P. Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, RFC 5382, DOI 10.17487/RFC5382, 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, DOI 10.17487/RFC6146, April 2011.
[RFC6302] Durand, A., Gashinsky, I., Lee, D. and S. Sheppard, "Logging Recommendations for Internet-Facing Servers", BCP 162, RFC 6302, DOI 10.17487/RFC6302, June 2011.
[RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A. and H. Ashida, "Common Requirements for Carrier-Grade NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888, April 2013.
[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, DOI 10.17487/RFC7011, September 2013.
[RFC7659] Perreault, S., Tsou, T., Sivakumar, S. and T. Taylor, "Definitions of Managed Objects for Network Address Translators (NATs)", RFC 7659, DOI 10.17487/RFC7659, October 2015.

9.2. Informative References

[I-D.ietf-behave-syslog-nat-logging] Chen, Z., Zhou, C., Tsou, T. and T. Taylor, "Syslog Format for NAT Logging", Internet-Draft draft-ietf-behave-syslog-nat-logging-06, January 2014.
[IPFIX-IANA] IANA, "IPFIX Information Elements registry"
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address Translator (NAT) Terminology and Considerations", RFC 2663, DOI 10.17487/RFC2663, August 1999.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, DOI 10.17487/RFC3022, January 2001.
[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008.
[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, DOI 10.17487/RFC5424, March 2009.

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
Renaldo Penno Cisco Systems 170 W Tasman Drive San Jose, California 95035 USA EMail: repenno@cisco.com