Request for Comments: 8158
Category: Standards Track
ISSN: 2070-1721
R. Penno
Cisco Systems
December 2017
IP Flow Information Export (IPFIX) Information Elements
for Logging NAT Events
Abstract
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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. In many cases, the logs are essential 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 use proprietary formats; hence, it is difficult to expect consistent behavior. This lack of standardization 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 NAT events.
Status of This Memo
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This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8158.
Copyright Notice
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Copyright © 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 (https://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
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 5 2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Deployment . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Event-Based Logging . . . . . . . . . . . . . . . . . . . . . 6 4.1. Logging Destination Information . . . . . . . . . . . . . 6 4.2. Information Elements . . . . . . . . . . . . . . . . . . 7 4.3. Definition of NAT Events . . . . . . . . . . . . . . . . 11 4.4. Quota Exceeded Event Types . . . . . . . . . . . . . . . 12 4.5. Threshold Reached Event Types . . . . . . . . . . . . . . 13 4.6. Templates for NAT Events . . . . . . . . . . . . . . . . 14 4.6.1. NAT44 Session Create and Delete Events . . . . . . . 14 4.6.2. NAT64 Session Create and Delete Events . . . . . . . 15 4.6.3. NAT44 BIB Create and Delete Events . . . . . . . . . 16 4.6.4. NAT64 BIB Create and Delete Events . . . . . . . . . 16 4.6.5. Addresses Exhausted Event . . . . . . . . . . . . . . 17 4.6.6. Ports Exhausted Event . . . . . . . . . . . . . . . . 17 4.6.7. Quota Exceeded Events . . . . . . . . . . . . . . . . 18 4.6.7.1. Maximum Session Entries Exceeded . . . . . . . . 18 4.6.7.2. Maximum BIB Entries Exceeded . . . . . . . . . . 18 4.6.7.3. Maximum Entries per User Exceeded . . . . . . . . 19 4.6.7.4. Maximum Active Hosts or Subscribers Exceeded . . 19 4.6.7.5. Maximum Fragments Pending Reassembly Exceeded . . 19 4.6.8. Threshold Reached Events . . . . . . . . . . . . . . 20 4.6.8.1. Address Pool High or Low Threshold Reached . . . 20 4.6.8.2. Address and Port Mapping High Threshold Reached . 21 4.6.8.3. Address and Port Mapping per User High Threshold Reached . . . . . . . . . . . . . . . . . . . . . 21 4.6.8.4. Global Address Mapping High Threshold Reached . . 22 4.6.9. Address Binding Create and Delete Events . . . . . . 22 4.6.10. Port Block Allocation and De-allocation . . . . . . . 22 5. Management Considerations . . . . . . . . . . . . . . . . . . 23 5.1. Ability to Collect Events from Multiple NAT Devices . . . 23 5.2. Ability to Suppress Events . . . . . . . . . . . . . . . 24 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 6.1. Information Elements . . . . . . . . . . . . . . . . . . 24 6.1.1. natInstanceID . . . . . . . . . . . . . . . . . . . . 24 6.1.2. internalAddressRealm . . . . . . . . . . . . . . . . 24 6.1.3. externalAddressRealm . . . . . . . . . . . . . . . . 25 6.1.4. natQuotaExceededEvent . . . . . . . . . . . . . . . . 25 6.1.5. natThresholdEvent . . . . . . . . . . . . . . . . . . 26 6.1.6. natEvent . . . . . . . . . . . . . . . . . . . . . . 27 6.1.7. maxSessionEntries . . . . . . . . . . . . . . . . . . 27 6.1.8. maxBIBEntries . . . . . . . . . . . . . . . . . . . . 28 6.1.9. maxEntriesPerUser . . . . . . . . . . . . . . . . . . 28 6.1.10. maxSubscribers . . . . . . . . . . . . . . . . . . . 28 6.1.11. maxFragmentsPendingReassembly . . . . . . . . . . . . 29 6.1.12. addressPoolHighThreshold . . . . . . . . . . . . . . 29 6.1.13. addressPoolLowThreshold . . . . . . . . . . . . . . . 29 6.1.14. addressPortMappingHighThreshold . . . . . . . . . . . 30 6.1.15. addressPortMappingLowThreshold . . . . . . . . . . . 30 6.1.16. addressPortMappingPerUserHighThreshold . . . . . . . 30 6.1.17. globalAddressMappingHighThreshold . . . . . . . . . . 31 7. Security Considerations . . . . . . . . . . . . . . . . . . . 31 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 8.1. Normative References . . . . . . . . . . . . . . . . . . 32 8.2. Informative References . . . . . . . . . . . . . . . . . 33 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
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The IP Flow Information Export (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) that can be carried by the IPFIX protocol. This document details the IPFIX 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 [NAT-LOG] are written in order to standardize the events and parameters to be recorded using IPFIX [RFC7011] and SYSLOG [RFC5424], respectively. 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 it is an IETF standard that meets all the needs for a reliable logging mechanism. IPFIX provides the flexibility to the logging device to define the datasets that it is logging. The IEs specified for logging must be the same irrespective of the encoding mechanism used.
1.1. Terminology
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The term "NAT device" in this document refers to any NAT44 or NAT64 device. The term "Collector" refers to any device that receives binary data from a NAT device and converts it into meaningful information. This document uses the term "session" as defined in [RFC2663], and the term "Binding Information Base" (BIB) as defined in [RFC6146]. The term "Information Element" or "IE" is defined in [RFC7011]. The term "Carrier-Grade NAT" refers to a large-scale NAT device as described in [RFC6888]
The IPFIX IEs that are NAT specific are created with NAT terminology. In order to avoid creating duplicates, IEs are reused if they convey the same meaning. This document uses the term "timestamp" for the IE, which defines the time when an event is logged; this is the same as the IPFIX term "observationTimeMilliseconds" as described in [IPFIX-IANA]. Since observationTimeMilliseconds is not self- explanatory for NAT implementors, the term "timeStamp" is used. Event templates, which refer to IPFIX Template Records, as well as log events, which refer to IPFIX Flow Records, are also used in this document.
1.2. Requirements Language
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
2. Scope
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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 transport protocols like TCP, UDP, or Stream Control Transmission Protocol (SCTP), which are 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.
This document uses the allocated IPFIX IEs in the IANA "IPFIX Information Elements" registry [IPFIX-IANA] and registers some new ones.
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 are 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
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NAT logging based on IPFIX uses binary encoding; hence, it 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 in line with the operator and the local jurisdiction. 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, the need for additional IP addresses, and etc. The deployment of NAT logging is not limited to just these cases.
4. Event-Based Logging
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An event in a NAT device can be viewed as a state transition because 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, 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 is provided in Table 2. Each of these events SHOULD be logged, unless this is 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 specification in [RFC7011].
4.1. Logging Destination Information
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Logging destination information in a NAT event is discussed in [RFC6302] and [RFC6888]. Logging 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 the source and destination addresses results in loss of privacy. Logging of destination addresses and ports, pre- or post-NAT, SHOULD NOT be done [RFC6888]. However, this document provides the necessary fields to log the destination information in cases where they must be logged.
4.2. Information Elements
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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:
{sourceIPv4Address, postNATSourceIPv4Address, destinationIPv4Address, postNATDestinationIPv4Address, sourceTransportPort, postNAPTSourceTransportPort, destinationTransportPort, postNAPTDestinationTransportPort, 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 table includes all the IEs that a NAT device would need to export the events. The formats of the IEs and the IPFIX IDs are listed. Detailed descriptions of the fields natInstanceID, internalAddressRealm, externalAddressRealm, natQuotaExceededEvent, and natThresholdEvent are included in the IANA Considerations section.
+-----------------------------------+--------+-------+--------------+ | Field Name | Size | IANA | Description | | | (bits) | IPFIX | | | | | ID | | +-----------------------------------+--------+-------+--------------+ | timeStamp | 64 | 323 | System Time | | | | | when the | | | | | event | | | | | occurred | | | | | | | natInstanceID | 32 | 463 | 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 | | | | | address | | | | | | | postNATDestinationIPv6Address | 128 | 282 | Translated | | | | | Destination | | | | | IPv6 address | | | | | | | internalAddressRealm | (*) | 464 | Source | | | | | Address | | | | | Realm | | | | | | | externalAddressRealm | (*) | 465 | 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 | 466 | Limit event | | | | | identifier | | | | | | | natThresholdEvent | 32 | 467 | Threshold | | | | | event | | | | | identifier | | | | | | | maxSessionEntries | 32 | 471 | Maximum | | | | | session | | | | | entries | | | | | | | maxBIBEntries | 32 | 472 | Maximum bind | | | | | entries | | | | | | | maxEntriesPerUser | 32 | 473 | Maximum | | | | | entries per- | | | | | user | | | | | | | maxSubscribers | 32 | 474 | Maximum | | | | | subscribers | | | | | | | maxFragmentsPendingReassembly | 32 | 475 | Maximum | | | | | fragments | | | | | for | | | | | ressembly | | | | | | | addressPoolHighThreshold | 32 | 476 | High | | | | | threshold | | | | | for address | | | | | pool | | | | | | | addressPoolLowThreshold | 32 | 477 | Low | | | | | threshold | | | | | for address | | | | | pool | | | | | | | addressPortMappingHighThreshold | 32 | 478 | High | | | | | threshold | | | | | for | | | | | address/port | | | | | mapping | | | | | | | addressPortMappingLowThreshold | 32 | 479 | Low | | | | | threshold | | | | | for | | | | | address/port | | | | | mapping | | | | | | | addressPortMappingPerUserHighThre | 32 | 480 | High | | shold | | | threshold | | | | | for per-user | | | | | address/port | | | | | mapping | | | | | | | globalAddressMappingHighThreshold | 32 | 481 | High | | | | | threshold | | | | | for global | | | | | address | | | | | mapping | +-----------------------------------+--------+-------+--------------+
Note: (*) indicates octetArray
Table 1: NAT IE List
4.3. Definition of NAT Events
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The following is the complete list of NAT events and the proposed event type values. The natEvent IE is defined in the "IPFIX Information Elements" registry [IPFIX-IANA];. 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" and are listed here for the sole purpose of completeness. Any compliant implementation SHOULD NOT use the events that are marked "Historic". These values were defined prior to the existence of this document and outside the IETF. These events are not standalone and require more information to be conveyed to qualify the event. For example, the NAT translation create event does not specify if it is NAT44 or NAT64. As a result, the Behave working group decided to have an explicit definition for each one of the unique events.
+-------+------------------------------------+ | Value | Event Name | +-------+------------------------------------+ | 0 | Reserved | | 1 | NAT translation create (Historic) | | 2 | NAT translation delete (Historic) | | 3 | NAT Addresses exhausted | | 4 | NAT44 session create | | 5 | NAT44 session delete | | 6 | NAT64 session create | | 7 | NAT64 session delete | | 8 | NAT44 BIB create | | 9 | NAT44 BIB delete | | 10 | NAT64 BIB create | | 11 | NAT64 BIB delete | | 12 | NAT ports exhausted | | 13 | Quota Exceeded | | 14 | Address binding create | | 15 | Address binding delete | | 16 | Port block allocation | | 17 | Port block de-allocation | | 18 | Threshold Reached | +-------+------------------------------------+
Table 2: NAT Event ID
4.4. Quota Exceeded Event Types
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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 have been reached or exceeded. The following table shows the sub-event types for the Quota Exceeded 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 or subscribers limit reached, and maximum Fragments pending reassembly limit reached.
+-------+---------------------------------------+ | Value | Quota Exceeded Event Name | +-------+---------------------------------------+ | 0 | Reserved | | 1 | Maximum session entries | | 2 | Maximum BIB entries | | 3 | Maximum entries per user | | 4 | Maximum active hosts or subscribers | | 5 | Maximum fragments pending reassembly | +-------+---------------------------------------+
Table 3: Quota Exceeded Event
4.5. Threshold Reached Event Types
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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 the Quota Exceeded and Threshold Reached events is that, once the Quota Exceeded events are hit, the packets are dropped or mappings will not be created, 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 either the operator might have to add more addresses to the pool or 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 utilizes 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 threshold event will then be triggered so that the global IPv4 address can be reclaimed.
The global address mapping high threshold event is generated when the maximum number of mappings per user is reached for a NAT device doing paired-address pooling.
+-------+---------------------------------------------------------+ | Value | Threshold Exceeded Event Name | +-------+---------------------------------------------------------+ | 0 | Reserved | | 1 | Address pool high threshold event | | 2 | Address pool low threshold event | | 3 | Address and port mapping high threshold event | | 4 | Address and port mapping per user high threshold event | | 5 | Global address mapping high threshold event | +-------+---------------------------------------------------------+
Table 4: Threshold Event
4.6. Templates for NAT Events
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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 IEs in the templates. Depending on the implementation and configuration, various IEs that are not mandatory can be included or ignored.
4.6.1. NAT44 Session Create and Delete Events
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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.
+----------------------------------+-------------+-----------+ | 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 | 16/32 | No | | internalAddressRealm | octetArray | No | | externalAddressRealm | octetArray | No | +----------------------------------+-------------+-----------+
Table 5: NAT44 Session Delete/Create Template
4.6.2. NAT64 Session Create and Delete Events
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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 | | 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 | 16/32 | No | | internalAddressRealm | octetArray | No | | externalAddressRealm | octetArray | No | +----------------------------------+-------------+-----------+
Table 6: NAT64 Session Create/Delete Event Template
4.6.3. NAT44 BIB Create and Delete Events
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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 | | natEvent | 8 | Yes | | sourceIPv4Address | 32 | Yes | | postNATSourceIPv4Address | 32 | Yes | | protocolIdentifier | 8 | No | | sourceTransportPort | 16 | No | | postNAPTSourceTransportPort | 16 | No | | natInstanceID | 32 | No | | vlanID/ingressVRFID | 16/32 | No | | internalAddressRealm | octetArray | No | | externalAddressRealm | octetArray | No | +-----------------------------+-------------+-----------+
Table 7: NAT44 BIB Create/Delete Event Template
4.6.4. NAT64 BIB Create and Delete Events
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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 | | natEvent | 8 | Yes | | sourceIPv6Address | 128 | Yes | | postNATSourceIPv4Address | 32 | Yes | | protocolIdentifier | 8 | No | | sourceTransportPort | 16 | No | | postNAPTSourceTransportPort | 16 | No | | natInstanceID | 32 | No | | vlanID/ingressVRFID | 16/32 | No | | internalAddressRealm | octetArray | No | | externalAddressRealm | octetArray | No | +-----------------------------+-------------+-----------+
Table 8: NAT64 BIB Create/Delete Event Template
4.6.5. Addresses Exhausted Event
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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.
+---------------+-------------+-----------+ | Field Name | Size (bits) | Mandatory | +---------------+-------------+-----------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natPoolID | 32 | Yes | | natInstanceID | 32 | No | +---------------+-------------+-----------+
Table 9: Addresses Exhausted Event Template
4.6.6. Ports Exhausted Event
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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 | | natEvent | 8 | Yes | | postNATSourceIPv4Address | 32 | Yes | | protocolIdentifier | 8 | Yes | | natInstanceID | 32 | No | +--------------------------+-------------+-----------+
Table 10: Ports Exhausted Event Template
4.6.7. Quota Exceeded Events
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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
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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.
+-----------------------+-------------+-----------+ | Field Name | Size (bits) | Mandatory | +-----------------------+-------------+-----------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natQuotaExceededEvent | 32 | Yes | | maxSessionEntries | 32 | Yes | | natInstanceID | 32 | No | +-----------------------+-------------+-----------+
Table 11: Session Entries Exceeded Event Template
4.6.7.2. Maximum BIB Entries Exceeded
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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.
+-----------------------+-------------+-----------+ | Field Name | Size (bits) | Mandatory | +-----------------------+-------------+-----------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natQuotaExceededEvent | 32 | Yes | | maxBIBEntries | 32 | Yes | | natInstanceID | 32 | No | +-----------------------+-------------+-----------+
Table 12: BIB Entries Exceeded Event Template
4.6.7.3. Maximum Entries per User Exceeded
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This event is generated when a single user reaches the administratively configured NAT translation limit. The following is the template of the event.
+-----------------------+-------------+---------------+ | Field Name | Size (bits) | Mandatory | +-----------------------+-------------+---------------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natQuotaExceededEvent | 32 | Yes | | maxEntriesPerUser | 32 | Yes | | sourceIPv4Address | 32 | Yes for NAT44 | | sourceIPv6Address | 128 | Yes for NAT64 | | natInstanceID | 32 | No | | vlanID/ingressVRFID | 16/32 | No | +-----------------------+-------------+---------------+
Table 13: Per-User Entries Exceeded Event Template
4.6.7.4. Maximum Active Hosts 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 | | natEvent | 8 | Yes | | natQuotaExceededEvent | 32 | Yes | | maxSubscribers | 32 | Yes | | natInstanceID | 32 | No | +-----------------------+-------------+-----------+
Table 14: Maximum Hosts/Subscribers Exceeded Event Template
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 the 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.
+-------------------------------+-------------+----------------+ | Field Name | Size (bits) | Mandatory | +-------------------------------+-------------+----------------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natQuotaExceededEvent | 32 | Yes | | maxFragmentsPendingReassembly | 32 | Yes | | sourceIPv4Address | 32 | Yes for NAT44 | | sourceIPv6Address | 128 | Yes for NAT64 | | natInstanceID | 32 | No | | vlanID/ingressVRFID | 16/32 | No | | internalAddressRealm | octetArray | No | +-------------------------------+-------------+----------------+-
Table 15: Maximum Fragments Pending Reassembly Exceeded Event
-
Template
4.6.8. Threshold Reached Events
-
This event will be generated when a NAT device reaches an 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
+----------------------------------------------+--------+-----------+ | Field Name | Size | Mandatory | | | (bits) | | +----------------------------------------------+--------+-----------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natThresholdEvent | 32 | Yes | | natPoolID | 32 | Yes | | addressPoolHighThreshold/ | 32 | Yes | | addressPoolLowThreshold | | | | natInstanceID | 32 | No | +----------------------------------------------+--------+-----------+
-
Table 16: Address Pool High/Low Threshold Reached Event Template
-
4.6.8.2. Address and Port Mapping High Threshold Reached
-
This event is generated when the high threshold is reached for the address pool and ports.
+----------------------------------------------+--------+-----------+ | Field Name | Size | Mandatory | | | (bits) | | +----------------------------------------------+--------+-----------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natThresholdEvent | 32 | Yes | | addressPortMappingHighThreshold/ | 32 | Yes | | addressPortMappingLowThreshold | | | | natInstanceID | 32 | No | +----------------------------------------------+--------+-----------+
-
Table 17: Address Port High Threshold Reached Event Template
-
4.6.8.3. Address and Port Mapping per User High Threshold Reached
-
This event is generated when the high threshold is reached for the per-user address pool and ports.
+----------------------------------------------+--------+-----------+ | Field Name | Size | Mandatory | | | (bits) | | +----------------------------------------------+--------+-----------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natThresholdEvent | 32 | Yes | | addressPortMappingHighThreshold/ | 32 | Yes | | addressPortMappingLowThreshold | | | | sourceIPv4Address | 32 | Yes for | | | | NAT44 | | sourceIPv6Address | 128 | Yes for | | | | NAT64 | | natInstanceID | 32 | No | | vlanID/ingressVRFID | 16/32 | No | +----------------------------------------------+--------+-----------+
Table 18: Address and Port Mapping per User High Threshold Reached
Event Template
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.
+-----------------------------------+-------------+-----------+ | Field Name | Size (bits) | Mandatory | +-----------------------------------+-------------+-----------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | natThresholdEvent | 32 | Yes | | globalAddressMappingHighThreshold | 32 | Yes | | natInstanceID | 32 | No | | vlanID/ingressVRFID | 16/32 | No | +-----------------------------------+-------------+-----------+-
Table 19: Global Address Mapping High Threshold Reached Event
-
Template
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.
+--------------------------+-------------+---------------+ | Field Name | Size (bits) | Mandatory | +--------------------------+-------------+---------------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | sourceIPv4Address | 32 | Yes for NAT44 | | sourceIPv6Address | 128 | Yes for NAT64 | | postNATSourceIPv4Address | 32 | Yes | | natInstanceID | 32 | No | +--------------------------+-------------+---------------+
Table 20: NAT Address Binding Template
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 to potentially 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.
+--------------------------+-------------+---------------+ | Field Name | Size (bits) | Mandatory | +--------------------------+-------------+---------------+ | timeStamp | 64 | Yes | | natEvent | 8 | Yes | | sourceIPv4Address | 32 | Yes for NAT44 | | sourceIPv6Address | 128 | Yes for NAT64 | | postNATSourceIPv4Address | 32 | Yes | | portRangeStart | 16 | Yes | | portRangeEnd | 16 | No | | natInstanceID | 32 | No | +--------------------------+-------------+---------------+
Table 21: NAT Port Block Allocation Event Template
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 fulfill these requirements is out of scope of the present document. Some management considerations are covered in [NAT-LOG]. 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 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; hence, they SHOULD be handled by the NAT devices to rate-limit them before sending them to the Collectors. For example, 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. IANA Considerations
6.1. Information Elements
-
IANA has registered the following IEs in the "IPFIX Information Elements" registry at [IPFIX-IANA].
6.1.1. natInstanceID
-
ElementID:
-
-
Name:
natInstanceID
Description: This Information Element uniquely identifies an Instance of the NAT that runs on a NAT middlebox function after the packet passes the Observation Point. natInstanceID is defined in [RFC7659].
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC791] for the definition of the IPv4 source address field. See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.2. internalAddressRealm
-
ElementID:
-
-
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 Virtual Routing and Forwarding (VRF) ID, 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 [RFC791] for the definition of the IPv4 source address field. See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.3. externalAddressRealm
-
ElementID:
-
-
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 [RFC791] for the definition of the IPv4 source address field. See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.4. natQuotaExceededEvent
-
ElementID:
-
-
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 Exceeded Event Type" registry, see [IPFIX-IANA]. Initial values in the registry are defined by the table below. New assignments of values will be administered by IANA and are subject to Expert Review [RFC8126]. Experts need to check definitions of new values for completeness, accuracy, and redundancy.
+--------+---------------------------------------+ | Value | Quota Exceeded Event Name | +--------+---------------------------------------+ | 0 | Reserved | | 1 | Maximum session entries | | 2 | Maximum BIB entries | | 3 | Maximum entries per user | | 4 | Maximum active hosts or subscribers | | 5 | Maximum fragments pending reassembly | +--------+---------------------------------------+
Note: This is the same as Table 3.
-
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC791] for the definition of the IPv4 source address field. See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.5. natThresholdEvent
-
ElementID:
-
-
Name:
natThresholdEvent
Description: This Information Element identifies a type of a NAT Threshold event. Values for this Information Element are listed in the "NAT Threshold Event Type" registry, see [IPFIX-IANA]. Initial values in the registry are defined by the table below. New assignments of values will be administered by IANA and are subject to Expert Review [RFC8126]. Experts need to check definitions of new values for completeness, accuracy, and redundancy.
+--------+---------------------------------------------------------+ | Value | Threshold Exceeded Event Name | +--------+---------------------------------------------------------+ | 0 | Reserved | | 1 | Address pool high threshold event | | 2 | Address pool low threshold event | | 3 | Address and port mapping high threshold event | | 4 | Address and port mapping per user high threshold event | | 5 | Global address mapping high threshold event | +--------+---------------------------------------------------------+
Note: This is the same as Table 4.
-
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC791] for the definition of the IPv4 source address field. See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.6. natEvent
-
The original definition of this Information Element specified only three values: 1, 2, and 3. This definition has been replaced by a registry, to which new values can be added. The semantics of the three originally defined values remain unchanged. IANA maintains the "NAT Event Type (Value 230)" registry for values of this Information Element at [IPFIX-IANA].
ElementID:
-
-
Name:
natEvent
Description: This Information Element identifies a NAT event. This IE identifies the type of a NAT event. Examples of NAT events include, but are not limited to, NAT translation create, NAT translation delete, Threshold Reached, or Threshold Exceeded, etc. Values for this Information Element are listed in the "NAT Event Type" registry, see [IPFIX-IANA]. The NAT event values in the registry are defined by Table 2 in Section 4.3. New assignments of values will be administered by IANA and are subject to Expert Review [RFC8126]. Experts need to check definitions of new values for completeness, accuracy, and redundancy.
Abstract Data Type: unsigned8
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes. See RFC 8158 for the definitions of values 4-16.
6.1.7. maxSessionEntries
-
ElementID:
-
-
Name:
maxSessionEntries
Description: This element represents the maximum session entries that can be created by the NAT device.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.8. maxBIBEntries
-
ElementID:
-
-
Name:
maxBIBEntries
Description: This element represents the maximum BIB entries that can be created by the NAT device.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.9. maxEntriesPerUser
-
ElementID:
-
-
Name:
maxEntriesPerUser
Description: This element represents the maximum NAT entries that can be created per user by the NAT device.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.10. maxSubscribers
-
ElementID:
-
-
Name:
maxSubscribers
Description: This element represents the maximum subscribers or maximum hosts that are allowed by the NAT device.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.11. maxFragmentsPendingReassembly
-
ElementID:
-
-
Name:
maxFragmentsPendingReassembly
Description: This element represents the maximum fragments that the NAT device can store for reassembling the packet.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.12. addressPoolHighThreshold
-
ElementID:
-
-
Name:
addressPoolHighThreshold
Description: This element represents the high threshold value of the number of public IP addresses in the address pool.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.13. addressPoolLowThreshold
-
ElementID:
-
-
Name:
addressPoolLowThreshold
Description: This element represents the low threshold value of the number of public IP addresses in the address pool.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.14. addressPortMappingHighThreshold
-
ElementID:
-
-
Name:
addressPortMappingHighThreshold
Description: This element represents the high threshold value of the number of address and port mappings.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.15. addressPortMappingLowThreshold
-
ElementID:
-
-
Name:
addressPortMappingLowThreshold
Description: This element represents the low threshold value of the number of address and port mappings.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.16. addressPortMappingPerUserHighThreshold
-
ElementID:
-
-
Name:
addressPortMappingPerUserHighThreshold
Description: This element represents the high threshold value of the number of address and port mappings that a single user is allowed to create on a NAT device.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes.
6.1.17. globalAddressMappingHighThreshold
-
ElementID:
-
-
Name:
globalAddressMappingHighThreshold
Description: This element represents the high threshold value of the number of address and port mappings that a single user is allowed to create on a NAT device in a paired address pooling behavior.
Abstract Data Type: unsigned32
Data Type Semantics: identifier
Reference: See [RFC3022] for the definition of NAT. See [RFC3234] for the definition of middleboxes. See [RFC4787] for the definition of paired address pooling behavior.
7. Security Considerations
-
The security considerations listed in detail for IPFIX in [RFC7011] apply to this document 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 Transport Layer Security (TLS) or Datagram Transport Layer Security (DTLS) for exchanging the log messages between the NAT device and the Collector. The log events sent in cleartext can result in confidential data being exposed to attackers, who could then spoof log events based on the information in cleartext messages. Hence, the log events SHOULD NOT be sent in cleartext.
The logging of NAT events can result in privacy concerns as a result of exporting information such as the source address and port information. The logging of destination 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.
8. References
8.1. 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, <https://www.rfc-editor.org/info/rfc2119>. [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 2007, <https://www.rfc-editor.org/info/rfc4787>. [RFC5382] Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, RFC 5382, DOI 10.17487/RFC5382, October 2008, <https://www.rfc-editor.org/info/rfc5382>. [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, <https://www.rfc-editor.org/info/rfc6146>. [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, <https://www.rfc-editor.org/info/rfc6302>. [RFC6888] Perreault, S., Ed., 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, <https://www.rfc-editor.org/info/rfc6888>. [RFC7011] Claise, B., Ed., Trammell, B., Ed., 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, <https://www.rfc-editor.org/info/rfc7011>. [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, <https://www.rfc-editor.org/info/rfc7659>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
-
[IPFIX-IANA]
IANA, "IPFIX Information Elements", <http://www.iana.org/assignments/ipfix>. [NAT-LOG] Chen, Z., Zhou, C., Tsou, T., and T. Taylor, Ed., "Syslog Format for NAT Logging", Work in Progress, draft-ietf- behave-syslog-nat-logging-06, January 2014. [RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, <https://www.rfc-editor.org/info/rfc791>. [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address Translator (NAT) Terminology and Considerations", RFC 2663, DOI 10.17487/RFC2663, August 1999, <https://www.rfc-editor.org/info/rfc2663>. [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, DOI 10.17487/RFC3022, January 2001, <https://www.rfc-editor.org/info/rfc3022>. [RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002, <https://www.rfc-editor.org/info/rfc3234>. [RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, DOI 10.17487/RFC5424, March 2009, <https://www.rfc-editor.org/info/rfc5424>. [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.
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.
Authors' Addresses
-
Senthil Sivakumar Cisco Systems 7100-8 Kit Creek Road Research Triangle Park, NC 27709 United States of America Phone: +1 919 392 5158 Email: ssenthil@cisco.com Reinaldo Penno Cisco Systems 170 W Tasman Drive San Jose, CA 95035 United States of America
Email:
repenno@cisco.com