Behave S. Sivakumar
Internet-Draft R. Penno
Intended status: Standards Track Cisco Systems
Expires: June 02, 2014 November 29, 2013

IPFIX Information Elements for logging NAT Events
draft-ietf-behave-ipfix-nat-logging-02

Abstract

NAT devices are required to log events like creation and deletion of translations and information about the resources it is managing. The logs are required 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 behave differently and hence it is difficult to expect a consistent behavior. The lack of a consistent way makes it difficult to write the collector applications that would receive this data and process it to present useful information. This document describes the information that is required to be logged by the NAT devices.

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 June 02, 2014.

Copyright Notice

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

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Table of Contents

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 [RFC5101bis].

2. Introduction

The IPFIX Protocol [RFC5101bis] 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 are required for logging by a NAT device. The document will specify the format of the IE's that are required to 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 [RFC5101bis] and SYSLOG [RFC5424]respectively.

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 devices including Carrier Grade NAT (CGN) events. This document focuses exclusively on the specification of IPFIX IE's. 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 contained in these elements is 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 are left to the implementation and are 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. 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.

5. Event based logging

An event in a NAT device can be viewed as a happening 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 should 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 are required to 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,

{sourceIPv4Adress, postNATSourceIPv4Address, destinationIpv4Address, postNATDestinationIPv4Address, sourceTransportPort, postNAPTSourceTransportPort, destinationTransportPort, postNAPTDestTransportPort, natOriginatingAddressRealm, 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 should support receiving multiple templates from the same source.


















































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.

Template format Table
Field Name Size (bits) IANA IPFIX ID Description
timeStamp 64 323 System Time when the event occured.
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
destinationIPv6Address 128 28 Destination IPv6 address
postNATSourceIPv6Address 128 281 Translated source IPv6 addresss
postNATDestinationIPv6Address 128 282 Translated Destination IPv6 address
natOriginatingAddressRealm 8 229 Address Realm
natEvent 8 230 Type of Event
portRangeStart 16 361 Allocated port block start
portRangeEnd 16 362 Allocated Port block end
portRangeStepSize 16 363 Step size of next port
portRangeNumPorts 16 364 Number of ports

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.

NAT Event ID table
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

5.4. Quota exceeded - natLimitEvent types

The following table shows the sub event types for the Quota exceeded event

Sub Event ID table
Quota Exceeded Event Name Values
Max Session entries 1
Max BIB entries 2
Max entries per user 3

5.5. Templates for NAT Events

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

5.5.1. 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.

NAT44 Session delete/create template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
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
natOriginatingAddressRealm 8 No
natEvent 8 Yes

5.5.2. 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
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
natOriginatingAddressRealm 8 No
natEvent 8 Yes

5.5.3. 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
vlanID/ingressVRFID 32 No
sourceIPv4Address 32 Yes
postNATSourceIPv4Address 32 Yes
protocolIdentifier 8 No
sourceTransportPort 16 No
postNAPTsourceTransportPort 16 No
natOriginatingAddressRealm 8 No
natEvent 8 Yes

5.5.4. 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
vlanID/ingressVRFID 32 No
sourceIPv6Address 128 Yes
postNATSourceIPv4Address 32 Yes
protocolIdentifier 8 No
sourceTransportPort 16 No
postNAPTsourceTransportPort 16 No
natOriginatingAddressRealm 8 No
natEvent 8 Yes

5.5.5. 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 wont 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.

NAT Address Exhausted event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natPoolName String Yes

5.5.6. 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.

NAT Ports Exhausted event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
postNATSourceIPv4Address 32 Yes
protocolIdentifier 8 Yes

5.5.7. Quota exceeded

This event will be generated when a NAT device cannot allocate resources as a result of an administratively defined policy. The examples of Quota exceeded are to allow only certain number of NAT sessions per device, certain number of NAT sessions per user etc. The following is a template of the event.

NAT Quota Exceeded event template
Field Name Size (bits) Mandatory
timeStamp 64 Yes
natEvent 8 Yes
natLimitEvent 32 Yes
sourceIPv4 address 32 Yes for NAT44
sourceIPv6 address 128 Yes for NAT64

5.5.8. 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.

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

5.5.9. 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.

portRangeNumPorts represents the number of ports that are allocated to the user.

portRangeStepSize represents the step size in case of non-contiguous port allocation.

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 must be specified. Along with portRangeStart, atleast one of portRangeEnd, portRangeStepSize or portRangeNumPorts MUST be specified. If portRangeEnd is specified, it MUST NOT be lesser than portRangeStart. The value of portRangeStepSize MUST be between 1 and 32K.

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
sourceIPv4 address 32 Yes for NAT44
sourceIPv6 address 128 Yes for NAT64
Translated Source IPv4 Address 32 Yes
portRangeStart 16 Yes
portRangeEnd 16 No
portRangeStepSize 16 No
portRangeNumPorts 16 No

6. Encoding

6.1. IPFIX

This document uses IPFIX as the encoding mechanism to describe the logging of NAT events. However, the information that should be 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 and Julia Renouard for their review and comments.

8. IANA Considerations

There are no IANA considerations for this document.

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.

9.1. Ability to collect events from multiple NAT devices

An IPFIX collector should 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.
[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

[RFC5470] Sadasivan, G., Brownlee, N., Claise, B. and J. Quittek, "Architecture for IP Flow Information Export", RFC 5470, March 2009.
[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-05, October 2013.
[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.
[IPFIX-IANA] IANA, "IPFIX Information Elements registry", .

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