One document matched: draft-ietf-behave-syslog-nat-logging-02.txt
Differences from draft-ietf-behave-syslog-nat-logging-01.txt
Internet Engineering Task Force Z. Chen
Internet-Draft China Telecom
Intended status: Standards Track C. Zhou
Expires: January 15, 2014 Huawei Technologies
T. Tsou
Huawei Technologies (USA)
T. Taylor
Huawei Technologies
July 14, 2013
Syslog Format for NAT Logging
draft-ietf-behave-syslog-nat-logging-02
Abstract
With the wide deployment of Carrier Grade NAT (CGN) devices, the
logging of NAT-related events has become very important for various
operational purposes. The logs may be required for troubleshooting,
to identify a host that was used to launch malicious attacks, and/or
for accounting purposes. This document identifies the events that
need to be logged and the parameters that are required in the logs
depending on the context in which the NAT is being used. It goes on
to standardize formats for reporting these events and parameters
using SYSLOG (RFC 5424). A companion document specifies formats for
reporting the same events and parameters using IPFIX (RFC 5101).
Applicability statements are provided in this document and its
companion to guide operators and implementors in their choice of
which technology to use for logging.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 15, 2014.
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Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Deployment Considerations . . . . . . . . . . . . . . . . . . 4
2.1. Static and Dynamic NATs . . . . . . . . . . . . . . . . . 4
2.2. NAT Logging Requirements For Different Transition Methods 5
2.3. The Port Control Protocol (PCP) . . . . . . . . . . . . . 6
2.4. Logging At the Customer Edge . . . . . . . . . . . . . . 6
3. NAT-Related Events and Parameters . . . . . . . . . . . . . . 6
3.1. NAT Session Creation and Deletion . . . . . . . . . . . . 7
3.1.1. Destination Logging . . . . . . . . . . . . . . . . . 8
3.2. Address Binding Event . . . . . . . . . . . . . . . . . . 8
3.3. Port Allocation Change . . . . . . . . . . . . . . . . . 9
3.4. NAT Address Exhaustion Event . . . . . . . . . . . . . . 9
3.5. Port Exhaustion Event . . . . . . . . . . . . . . . . . . 10
3.6. Quota Exceeded Event . . . . . . . . . . . . . . . . . . 10
3.7. Invalid Port Detected . . . . . . . . . . . . . . . . . . 11
3.8. Static NAT Configuration Event . . . . . . . . . . . . . 11
4. SYSLOG Applicability . . . . . . . . . . . . . . . . . . . . 11
5. SYSLOG Record Format For NAT Logging . . . . . . . . . . . . 12
5.1. SYSLOG HEADER Fields . . . . . . . . . . . . . . . . . . 13
5.2. Parameter Encodings . . . . . . . . . . . . . . . . . . . 13
5.2.1. APoolId: Address Pool Identifier . . . . . . . . . . 14
5.2.2. DevID: Reporting Device Identifier . . . . . . . . . 14
5.2.3. DevTyp: Reporting Device Type . . . . . . . . . . . . 14
5.2.4. PostS4: Mapped External IPv4 Address . . . . . . . . 15
5.2.5. PostSPt: Mapped External Port or ICMP Identifier . 15
5.2.6. PreSPt: Internal Port or ICMP Identifier . . . . . . 15
5.2.7. Proto: Protocol Identifier . . . . . . . . . . . . . 15
5.2.8. PScop: Protocol Scope For Quota . . . . . . . . . . . 15
5.2.9. PSID: Port Set Identifier . . . . . . . . . . . . . . 15
5.2.10. PtRg: Allocated Port Range . . . . . . . . . . . . . 15
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5.2.11. SiteID: Subscriber Site Identifier . . . . . . . . . 15
5.2.12. SScop: Site Scope For Quota . . . . . . . . . . . . . 16
5.2.13. TrigR: Realm Triggering Session Creation . . . . . . 16
5.2.14. VLANid: VLAN Identifier . . . . . . . . . . . . . . . 16
5.2.15. VRFid: VPN Routing and Forwarding Identifier . . . . 16
5.3. Encoding Of Complete Log Report For Each Event Type . . . 16
5.3.1. NAT Session Creation and Deletion . . . . . . . . . . 16
5.3.1.1. Examples . . . . . . . . . . . . . . . . . . . . 17
5.3.2. Address Binding Event . . . . . . . . . . . . . . . . 17
5.3.3. Port Allocation Change . . . . . . . . . . . . . . . 18
5.3.4. Address Exhaustion Event . . . . . . . . . . . . . . 19
5.3.5. NAT Port Exhaustion . . . . . . . . . . . . . . . . . 19
5.3.6. Quota Exceeded . . . . . . . . . . . . . . . . . . . 20
5.3.7. Invalid Port Detected . . . . . . . . . . . . . . . . 21
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.1. Normative References . . . . . . . . . . . . . . . . . . 24
8.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction
Operators already need to record the addresses assigned to
subscribers at any point in time, for operational and regulatory
reasons. When operators introduce NAT devices which support address
sharing (e.g., Carrier Grade NATs (CGNs)) into their network,
additional information has to be logged. This document and
[I-D.behave-ipfix-nat-logging] are provided in order to standardize
the events and parameters to be recorded, using SYSLOG [RFC5424] and
IPFIX [RFC5101] respectively. The content proposed to be logged by
the two documents is exactly the same, but as will be seen, the
choice of which to use in a given scenario is an engineering issue.
Detailed logging requirements will vary depending on the context in
which they are used. For example, different methods for transition
from IPv4 to IPv6 require different events and different parameters
to be logged. Section 2 covers this topic.
Section 3 provides a more detailed description of the events that
need logging and the parameters that may be required in the logs.
The use of SYSLOG [RFC5424] has advantages and disadvantages compared
with the use of IPFIX [RFC5101]. Section 4 provides a statement of
applicability for the SYSLOG approach.
Section 5 specifies SYSLOG record formats for logging of the events
and parameters described in Section 3. The definitions provide the
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flexibility to vary actual log contents based on the requirements of
the particular deployment.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in "Key words for use in
RFCs to Indicate Requirement Levels" [RFC2119].
This document uses the term "Session" as it is defined in Section 2.3
of [RFC2663] and the term Binding Information Base (BIB) as it is
defined in Section 2 of [RFC6146].
Except where a clear distinction is necessary, this document uses the
abbreviation "NAT" to encompass both Network Address Translation (NAT
in the strict sense) and Network Address and Port Translation (NAPT).
2. Deployment Considerations
2.1. Static and Dynamic NATs
A NAT controls a set of resources in the form of one or more pools of
external addresses. If the NAT also does port translation (i.e., it
is a NAPT), it also controls the sets of UDP and TCP port numbers and
ICMP identifiers associated with each external address.
Logging requirements for a NAT depend heavily on its resource
allocation strategy. NATs can be classed as static or dynamic
depending on whether the resources provided to individual users are
pre-configured or allocated in real time as the NAT recognizes new
flows.
Static assignments can be logged at configuration time by the NAT or
by network infrastructure. The logging volume associated with static
assignments will be relatively low, of the order of the volume of
user logons. As discussed below, static assignments are typically
associated with IPv6 transition methods rather than traditional NAT.
The details of what to log will depend on the transition method
concerned.
Dynamic assignments typically require both more detail in the logs
and a higher volume of logs in total. A traditional Network Address
Port Translator (NAPT) as described in [RFC3022] and following the
recommendations of [RFC4787] and [RFC5382] will generate a new
mapping each time it encounters a new internal <address, port>
combination.
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For statistical reasons, static assignments support lower address
sharing ratios than fully dynamic assignments as exemplified by the
traditional NAPT. The sharing ratio can be increased while
restraining log volumes by assigning ports to users in multi-port
increments as required rather than assigning just one port at a time.
A subscriber may start with no initial allocation, or may start with
an initial permanent allocation to which temporary increments are
added when the initial set is all being used. See [RFC6264] and
[I-D.tsou-behave-natx4-log-reduction] for details. If this strategy
is followed, logging will be required only when an increment is
allocated or reclaimed rather than every time an internal <address,
port> combination is mapped to an external <address, port>.
2.2. NAT Logging Requirements For Different Transition Methods
A number of transition technologies have been or are being developed
to aid in the transition from IPv4 to IPv6. 6rd [RFC5969] and DS-Lite
[RFC6333] are at the deployment stage. Several 'stateless'
technologies: Public IPv4 over IPv6 [I-D.softwire-public-4over6],
MAP-E [I-D.softwire-map], and Lightweight 4over6
[I-D.softwire-lw4over6] have seen experimental deployment and are in
the process of being standardized at the time of writing of this
document.
Of the technologies just listed, 6rd and Public IPv4 over IPv6 do not
involve NATs and hence need not be considered further. The other
techniques involve NAT at the customer edge, at the border router, or
both, and hence are in scope.
A DS-Lite Address Family Transition Router (AFTR) includes a large-
scale session-stateful NAT44 processing potentially millions of
sessions per second. The special character of AFTR operation over
that of a traditional NAT44 is that the source IPv4 addresses of the
interior hosts may not be unique. As a consequence, the session
tables need to include an alternative identifier associated with the
subscriber host. For basic DS-Lite, this will be the IPv6 address
used to encapsulate the packets outgoing from the host. See
Section 6.6 of [RFC6333]. For gateway-initiated DS-Lite [RFC6674],
an identifier associated with the incoming tunnel from the host is
used instead.
The DS-Lite customer edge equipment (the 'B4') may also perform NAT44
functions, similar to the functions performed by traditional NAT44
devices. This document does not include any requirements specific to
the B4, since logs are not usually collected from customer equipment.
As a NAT44, the DS-Lite AFTR may be fully dynamic, or may allocate
ports in increments as described in the previous section.
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Lightweight 4over6 [I-D.softwire-lw4over6] and MAP-E
[I-D.softwire-map] both require NAT44 operation at the customer
equipment (unified CPE, [I-D.softwire-unified-cpe]). In both cases
the resource allocation strategy is static. Thus any logging of
resource allocation for these two transition techniques can be done
by the network at configuration time.
The border router (BR), for either Lightweight 4over6 or MAP-E, is
required to monitor port usage by outgoing IPv4 packets. If the
ports used by a host fall outside its configured port set, the border
router may return an ICMPv6 type 1, code 5 (source address failed
ingress/egress policy) error message to the unified CPE. It is also
possible for the same reason that the unified CPE receives incoming
IPv4 packets with destination port numbers outside of its assigned
range.
Out-of-range ports are a sign of misconfiguration or other problems,
so it is reasonable for the BR to log such events (subject to the
rate limiting). The log should capture the port set that the BR
believes is configured on the unified CPE. For both Lightweight
4over6 and MAP-E, this is associated with an identifier, the 16-bit
port set identifier (PSID).
2.3. The Port Control Protocol (PCP)
The Port Control Protocol (PCP) [RFC6887] and its port set extension
[I-D.pcp-port-set] can be viewed as a way to provision ports by other
means. However, PCP can be invoked on a per-flow basis, so the
volume of logs generated by a PCP server can be closer to the volume
associated with a fully dynamic NAT. The volume really depends on
how PCP is being used in a specific network.
2.4. Logging At the Customer Edge
Logging at the customer edge (or at the ISP edge for NATs protecting
the ISP's internal networks) may be done by the customer for purposes
of internal management, or by the ISP for its own administrative and
regulatory purposes. Given the likelihood of a high internal
community of interest, it is possible but unlikely that a NAT at the
edge of a large enterprise network processes a number of new packet
flows per second which is comparable to the volume handled by a
carrier grade NAT. Most customer edge NATs will handle a much
smaller volume of flows.
3. NAT-Related Events and Parameters
The events which follow were initially gleaned, in the words of the
authors of [I-D.behave-ipfix-nat-logging], from [RFC4787] and
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[RFC5382]. Some details were subsequently informed by the discussion
in Section 2. Since the present document deals with SYSLOG rather
than IPFIX, the timestamp and the event type will appear in the log
header rather than as an explicit part of the structured data portion
of the log. Hence they are omitted from the parameter tabulations
that follow.
The listed parameters include an optional reporting device identifier
and an optional reporting device type in each case. The reporting
device identifier is potentially useful only if the HOSTNAME field in
the log header identifies an off-board device rather than the NAT
itself. The reporting device type identifies which of the reporting
device types listed in Section 5.2.3 is reporting the event.
Reference will be made below to a subscriber site identifier. IOn
practice, NATs use various means to distinguish customer endpoints,
and this will be reflected in what they log. From a strictly
theoretical point of view:
o For traditional NATs, the source IPv4 address (for NAT44) or IPv6
address (for NAT64) is sufficient.
o For the DS-Lite, Lightweight 4over6 or MAP-E transition methods,
the subscriber site can be identified by the IPv6 tunnel endpoint
prefix or address provisioned to that site.
o Gateway-initiated DS-Lite uses the combination of a 32-bit context
identifier (CID) and a softwire identifier (SWID). Several
different realizations of these identifiers are described in
Section 6 of [RFC6674].
3.1. NAT Session Creation and Deletion
NAT session creation and deletion events may be logged in a fully
dynamic NAT when a binding from a subscriber site identifier and
source port to an external address and port is recorded in or deleted
from the session database. See Section 3 of [RFC3022] for more
details about session creation and deletion.
The following specific events are defined:
o NAT Session Creation
o NAT Session Deletion
These take the same parameters for all types of NAT, aside from the
variation in subscriber site identifier noted above:
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o reporting device type (OPTIONAL);
o reporting device identifier (OPTIONAL);
o Subscriber site identifier (MANDATORY);
o Mapped external IPv4 address (MANDATORY);
o Protocol identifier (MANDATORY for NAPT);
o Internal port or ICMP identifier (MANDATORY for NAPT);
o Mapped external port or ICMP identifier (MANDATORY for NAPT);
o Address realm (internal or external) of the source of the packet
triggering the creation of the session (OPTIONAL).
3.1.1. Destination Logging
The logging of destination address and port for outgoing packets is
considered out of scope of this document, for several reasons.
[RFC6888] recommends against destination logging because of the
privacy issues it creates. From an operator's point of view,
destination logging is costly not just because of the volume of logs
it will generate, but because the NAT now has carry additional
session state so that it only needs to log once per session between
two transport end points rather than logging every packet. Finally,
[RFC4787], etc. recommend the use of endpoint-independent mapping to
maximize the ability of applications to operate through the NAT.
In short, destination logging will be a rarely-used procedure for
which standardization seems unnecessary.
3.2. Address Binding Event
This event is recorded at a dynamic or hybrid NAT when a given
subscriber site identifier has been bound to an external source
address. An address binding occurs when the first packet in the
first flow from the host in the internal realm is received at the
NAT. It MAY occur under other circumstances (e.g., PCP request, or
NAT policy permits assignment of a new external address due to port
conflict). The event parameters are:
o reporting device type (OPTIONAL);
o reporting device identifier (OPTIONAL);
o Subscriber site identifier (MANDATORY);
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o Mapped external IPv4 address (MANDATORY).
3.3. Port Allocation Change
This event is recorded at a hybrid NAT whenever the set of ports
allocated to a given address binding changes. When ports are
allocated, the same ports are allocated for UDP and for TCP. The
parameters for this event are:
o reporting device type (OPTIONAL);
o reporting device identifier (OPTIONAL);
o Subscriber site identifier (MANDATORY);
o Mapped external IPv4 address (MANDATORY);
o One or more contiguous port ranges specified by starting and
ending port number (MANDATORY).
The log MUST indicate the cumulative set of ports allocated to the
address binding (taking account both of allocations and
deallocations) at the time the log was generated. An implementation
MAY show each individual allocation as a separate range, or MAY
consolidate adjacent ranges. For example, suppose the address
binding is initially allocated the range 1024-1535. The log at the
time of the initial allocation will contain that one range. Suppose
now that an additional allocation is granted, consisting of the range
1536-2047. The log generated may contain the two ranges 1024-1535
and 1536-2047, or may contain the one consolidated range 1024-2047.
Finally, suppose that ports 1536-1791 are deallocated. The resulting
log will show the ranges 1024-1535 and 1792-2047 as the current
allocation to the address binding.
3.4. NAT Address Exhaustion 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 will not be able to create any new
translations until some addresses or ports are freed. This event
takes the following parameters:
o reporting device type (OPTIONAL);
o reporting device identifier (OPTIONAL);
o address pool identifier (MANDATORY).
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Implementations MUST provide the ability to limit the rate at which
this log is generated, since the NAT may move back and forth between
exhausted and almost-exhausted state many times during a particular
busy episode.
3.5. Port Exhaustion 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) individually. The event parameters are:
o reporting device type (OPTIONAL);
o reporting device identifier (OPTIONAL);
o Mapped external IPv4 address (MANDATORY);
o Protocol identifier (MANDATORY).
Implementations MUST provide the ability to limit the rate at which
this log is generated, since the NAT may move back and forth between
exhausted and almost-exhausted state many times during a particular
busy episode.
3.6. Quota Exceeded Event
A "Quota Exceeded" event is reported when the NAT cannot allocate a
new session because of an administratively imposed limit on the
number of sessions allowed for a given subscriber or set of
subscribers, for a given protocol or totalled over all protocols.
The parameters of this event are:
o reporting device type (OPTIONAL);
o reporting device identifier (OPTIONAL);
o Site scope (MANDATORY);
o Protocol (MANDATORY);
o Subscriber site identifier (OPTIONAL);
o VLAN identifier or VPN Routing and Forwarding (VRF) identifier
(OPTIONAL).
Site scope is either single site, multiple sites served by the same
VLAN or VRF, or all sites served by the NAT. If the site scope is
single site, then the subscriber site identifier MUST be present and
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the VLAN or VRF identifier MUST be absent. If the site scope is
multiple sites, then the reverse MUST be true. If the site scope is
all sites, the subscriber site identifier, the VRF idenbtifier, and
the VLAN identifier MUST NOT be present. Protocol scope is either a
specific protocol (UDP, TCP, ICMP) or all protocols, meaning that the
quota concerned applies to the total number of sessions supported by
the NAT regardless of protocol.
Implementations MUST provide the ability to limit the rate at which
this log is generated, since the NAT may move back and forth between
over-quota and within-quota state many times during a particular busy
episode.
3.7. Invalid Port Detected
As discussed in Section 2.2, this event may be reported at MAP-E or
Lightweight 4over6 Border Router, either through receipt of ICMP
error messages or by direct observation of incoming IPv4 packets.
List discussion has pointed out that enabling ICMP on the customer
edge device opens up the potential for denial of service attacks
on the Border Router. Hence direct observation will be the more
likely trigger for this event.
The event report takes the following parameters:
o reporting device identifier (OPTIONAL);
o Subscriber site identifier (MANDATORY);
o port set identifier for the subscriber site, as provisioned at the
Border Router (MANDATORY).
3.8. Static NAT Configuration Event
*** Should we anticipate logging of the configuration (IPv6 prefix,
IPv4 prefix/address, PSID) assigned to the Lightweight 4over6 or
MAP-E CPE? ***
4. SYSLOG Applicability
The primary advantage of SYSLOG is the human readability and
searchability of its contents. In addition, it has built-in priority
and severity fields that allow for separate routing of reports
requiring management action. Finally, it has a well-developed
underpinning of transport and security protocol infrastructure.
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SYSLOG presents two obstacles to scalability: the fact that the
records will typically be larger than records based on a binary
protocol such as IPFIX, and, depending on the architectural context,
the reduced performance of a router that is forced to do text
manipulation in the data plane. One has to conclude that for larger
message volumes, IPFIX should be preferred as the reporting medium on
the NAT itself. It is possible that SYSLOG could be used as a back-
end format on an off-board device processing IPFIX records in real
time, but this would give a limited boost to scalability. One
concern expressed in list discussion is that when the SYSLOG
formatting process gets overloaded records will be lost.
As a result, the key question is what the practical cutoff point is
for the expected volume of SYSLOG records, on-board or off-board the
NAT. This obviously depends on the computing power of the formatting
platform, and also on the record lengths being generated.
Information has been provided to the BEHAVE list at the time of
writing to the effect that one production application is generating
an average of 150,000 call detail records per second, varying in
length from 500 to 1500 bytes. Capacities several times this level
have been reported involving shorter records, but this particular
application has chosen to limit the average in order to handle peaks.
As illustrated by the examples in Section 5.3, typical record sizes
for the high-volume logs are in the order of 150 to 200 bytes, so
throughput capacity should be higher than in the call detail case for
the same amount of computing power. In private communication, a
discussant has noted a practical limit of a few hundred thousand
SYSLOG records per second on a router.
5. SYSLOG Record Format For NAT Logging
This section describes the SYSLOG record format for NAT logging in
terms of the field names used in [RFC5424] and specified in Section 6
of that document. In particular, this section specifies values for
the APP-NAME and MSGID fields in the record header, the SD-ID
identifying the STRUCTURED-DATA section, and the PARAM-NAMEs and
PARAM-VALUE types for the individual possible parameters within that
section. The specification is in three parts, covering the header,
encoding of the individual parameters, and encoding of the complete
log record for each event type.
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5.1. SYSLOG HEADER Fields
Within the HEADER portion of the SYSLOG record, the priority (PRI)
level is subject to local policy, but a default value of 8x is
suggested, representing a Facility value of 10 (security/
authorization) and a Severity level varying with the event type. The
suggested value by event type is shown in Table 1. Depending on
where the SYSLOG record is generated, the HOSTNAME field may identify
the NAT or an offline logging device. In the latter case, it may be
desirable to identify the NAT using the DevID field in the
STRUCTURED-DATA section (see below). The value of the HOSTNAME field
is subject to the preferences given in Section 6.2.4 of [RFC5424].
The values of the APP-NAME and MSGID fields in the record header
determine the semantics of the record. The APP-NAME value "NAT"
indicates that the record relates to an event reported by a NAT
device. The MSGID values indicate the individual events. They are
listed in Table 1 for each of the events defined in Section 3. The
table also shows the SD-ID value used to label the event-specific
STRUCTURED-DATA element.
+------------------------+----------+-------------+-----------+
| Event | MSGID | PRI | SD-ID |
+------------------------+----------+-------------+-----------+
| NAT session creation | SessAdd | 86 info | NATsess |
| NAT session deletion | SessDel | 86 info | NATsess |
| Address binding event | AddrBind | 86 info | NATBind |
| Port allocation change | PtAlloc | 86 info | NATPBlk |
| NAT address exhaustion | AddrEx | 82 critical | NATAddrEx |
| NAT port exhaustion | PortEx | 84 warning | NATPEx |
| Quota exceeded | Quota | 85 notice | NATQEx |
| Invalid port detected | InvPort | 83 error | NATInvP |
+------------------------+----------+-------------+-----------+
Table 1: Recommended MSGID Encodings and Default PRI Values for the
Events Defined In Section 3
5.2. Parameter Encodings
This section describes how to encode the individual parameters that
can appear in NAT-related logs. The parameters are taken from the
event descriptions in Section 3, and are listed in Table 2.
Formally, as will be seen in Table 10, a parameter used with more
than one event is registered as multiple separate parameters, one for
each event report in which it is used. However, there is no reason
to change either the PARAM-NAME or the encoding of the PARAM-VALUE
between different instances of the same parameter.
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+------------+------------------------------------------------------+
| PARAM-NAME | Parameter |
+------------+------------------------------------------------------+
| APoolId | Address pool identifier |
| DevID | reporting device identifier |
| DevTyp | reporting device type |
| PostS4 | Mapped external IPv4 address |
| PostSPt | Mapped external port or ICMP identifier |
| PreSPt | Internal port or ICMP identifier |
| Proto | Protocol identifier |
| PScop | Protocol scope for quota |
| PSID | Port set identifier |
| PtRg | Range of consecutive port numbers |
| SiteID | Subscriber site identifier |
| SScop | Site scope for quota |
| TrigR | Address realm triggering the creation of the session |
| VLANid | VLAN identifier |
| VRFid | VPN routing and forwarding identifier |
+------------+------------------------------------------------------+
Table 2: Parameters Used In NAT-Related Log Reports, By PARAM-NAME
5.2.1. APoolId: Address Pool Identifier
PARAM-Value: decimal integer identifying a specific address pool at
the reporting NAT.
5.2.2. DevID: Reporting Device Identifier
PARAM-VALUE: a UTF-8 string identifying the NAT or BR observing the
event which this record reports. Needed only if the necessary
identification is not provided by the HOSTNAME parameter in the log
record header.
5.2.3. DevTyp: Reporting Device Type
PARAM-VALUE: one of the values provided in the IANA SYSLOG reporting
device type registry established by this document. The initial
values in that registry are:
44 NAT44 [RFC3022];
64 NAT64 [RFC6145] or [RFC6146];
AFTR DS-Lite AFTR [RFC6333];
BR Lightweight 4over6 or MAP-E border router.
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This parameter is primarily additional information for the human
reader of a log report, but could be used to provide a consistency
check on the contents of a log. Instances where parameter usage
depends on the reporting device type of the reporting NAT are noted
in Section 5.3.
5.2.4. PostS4: Mapped External IPv4 Address
PARAM-VALUE: IPv4 address, represented in dotted decimal form.
5.2.5. PostSPt: Mapped External Port or ICMP Identifier
PARAM-Value: decimal integer, port number or ICMP query identifier.
5.2.6. PreSPt: Internal Port or ICMP Identifier
PARAM-Value: decimal integer, port number or ICMP query identifier.
5.2.7. Proto: Protocol Identifier
PARAM-VALUE: an integer indicating the value of the Protocol header
field (IPv4) or Next Header field (IPv6) in the incoming packet(s)
(after decapsulation, for reporting device type "AFTR") to which the
event described by this record applies.
5.2.8. PScop: Protocol Scope For Quota
PARAM-VALUE: as for Proto for a specific protocol. "*" for sum over
all protocols.
5.2.9. PSID: Port Set Identifier
PARAM-VALUE: integer between 0 and 65535 designating a port set. In
practice the upper limit is likely to be two orders of magnitude
smaller.
5.2.10. PtRg: Allocated Port Range
PARAM-VALUE: a field consisting of two decimal integers separated by
a minus sign/hyphen. The first integer is the lowest port number,
the second, the highest port number, in a range of consecutive ports.
5.2.11. SiteID: Subscriber Site Identifier
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A human-readable UTF-8 string identifying a specific host or CPE
served by the reporting device. The type of identifier depends on
the configuration of the reporting device, and is implementation and
deployment-specific. See Section 3 for a discussion of the possible
identifier types.
5.2.12. SScop: Site Scope For Quota
PARAM-VALUE: "S" for single site, "M" for sum over multiple sites,
served by the same VLAN or VRF. "*" for sum over all sites served by
the NAT.
5.2.13. TrigR: Realm Triggering Session Creation
PARAM-VALUE: "I" for internal, "E" for external.
5.2.14. VLANid: VLAN Identifier
PARAM-VALUE: a decimal integer representing the VLAN identifier
associated with the subscriber site.
5.2.15. VRFid: VPN Routing and Forwarding Identifier
PARAM-VALUE: a hexadecimal number representing a VPN identifier
[RFC2685] associated with the subscriber site. It is RECOMMENDED
that implementations be configurable to include or not include the
OUI portion of the identifier.
5.3. Encoding Of Complete Log Report For Each Event Type
This section describes the complete NAT-related contents of the logs
used to report the events listed in Table 1.
5.3.1. NAT Session Creation and Deletion
As shown in Table 1, the NAT session creation event is indicated by
MSG-ID set to "SessAdd". Similarly, the NAT session deletion event
is indicated by MSG-ID set to "SessDel". For both events, the
associated SD-ELEMENT is tagged by SD-ID "NATsess". The contents of
the NATsess SD-ELEMENT are shown in Table 3. The requirements for
these contents are derived from the description in Section 3.1.
+------------+----------------+-------------+
| PARAM-NAME | Description | Requirement |
+------------+----------------+-------------+
| DevTyp | Section 5.2.3 | OPTIONAL |
| DevID | Section 5.2.2 | OPTIONAL |
| SiteID | Section 5.2.11 | MANDATORY |
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| PostS4 | Section 5.2.4 | MANDATORY |
| Proto | Section 5.2.7 | MANDATORY |
| PreSPt | Section 5.2.6 | MANDATORY |
| PostSPt | Section 5.2.5 | MANDATORY |
| TrigR | Section 5.2.13 | OPTIONAL |
+------------+----------------+-------------+
Table 3: Contents Of the SD-ELEMENT Section For Logging the Session
Creation and Deletion Events
5.3.1.1. Examples
The first example is deliberately chosen to show how long a complete
session log might be. For this first example, assume the log is
formatted at an off-board device, which collects the information from
an AFTR. Thus HOSTNAME and DevID are both present. IPv6 addresses
are reported omitting a common /16 prefix and the IID portion of the
address (not to be too unrealistic!). All the optional parameters
are present. Note that the log could also include other SD-ELEMENTs
(e.g., timeQuality), but enough is enough.
The log appears as a single record, but is wrapped between lines for
purposes of presentation.
<86>1 2013-05-07T22:14:15.03Z record.example.net NAT 5063 SessAdd
[NATsess DevTyp="AFTR" DevID="bgw211.example.net"
SiteID="A2E0:62" PostS4="198.51.100.127"
Proto="6" PreSPt="49156" PostSPt="6083" TrigR="I"]
Character count: about 205.
The next example is perhaps more typical in size. Assume an
enterprise NAT44 generating its own logs. The optional parameters
are omitted. This is a session deletion event.
<86>1 2013-05-07T15:27:49.603-04:00 cerberus.example.com
NAT 175 SessDel [NATsess SiteID="192.0.2.5" PostS4="198.51.100.14"
Proto="6" PreSPt="51387" PostSPt="17865"]
The character count: about 165.
5.3.2. Address Binding Event
As shown in Table 1, the NAT address binding event is indicated by
MSG-ID set to "AddrBind". The associated SD-ELEMENT is tagged by SD-
ID "NATBind". The contents of the NATBind SD-ELEMENT are shown in
Table 4. The requirements for these contents are derived from the
description in Section 3.2.
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+------------+-----------------+-------------+
| PARAM-NAME | Description | Requirement |
+------------+-----------------+-------------+
| DevTyp | Section 5.2.3 | OPTIONAL |
| DevID | Section 5.2.2 | OPTIONAL |
| SiteID | Section 5.2.11 | MANDATORY |
| PostS4 | Section 5.2.4 | MANDATORY |
+------------+-----------------+-------------+
Table 4: Contents Of the SD-ELEMENT Section For Logging the Address
Binding Event
As an example, consider a DS-Lite AFTR [RFC6333] incorporating a PCP
server, where PCP is used to obtain an external address binding and a
port range. See Section 11 of [RFC6887] for the address binding.
(The port allocation is shown in the next section's example.) As in
the session creation example, the first /16 prefix and the final 64
bits are omitted from the encapsulating IPv6 address which is used as
the subscriber site identifier.
<86>1 2013-05-07T15:27:49.603Z yourd137mzmhow.example.net
NAT 68 AddrBind [NATBind SiteID="5A27:876E" PostS4="198.51.100.1"]
Character count: about 125.
5.3.3. Port Allocation Change
As indicated in Table 1, the port block allocation change event is
indicated by MSG-ID set to "PtAlloc". The associated SD-ELEMENT is
tagged by SD-ID "NATPBlk". The contents of the NATPBlk SD-ELEMENT
are shown in Table 5. The requirements for these contents are
derived from the description in Section 3.3.
+------------+----------------+-------------+
| PARAM-NAME | Description | Requirement |
+------------+----------------+-------------+
| DevTyp | Section 5.2.3 | OPTIONAL |
| DevID | Section 5.2.2 | OPTIONAL |
| SiteID | Section 5.2.11 | MANDATORY |
| PostS4 | Section 5.2.4 | MANDATORY |
| PtRg | Section 5.2.10 | MANDATORY |
+------------+----------------+-------------+
Table 5: Contents Of the SD-ELEMENT Section For Logging the Port
Allocation Change Event
As in the example in the previous section example, consider a DS-
Lite AFTR [RFC6333] incorporating a PCP server, where PCP is used to
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obtain an external address binding and a port range. See
[I-D.pcp-port-set] for the port set part of this operation.
Strictly for purposes of illustration, assume that the subscriber is
allocated two ranges of 64 consecutive values each, with the first
beginning at 2048 and the second at 4096.
<86>1 2013-05-07T15:27:49.751Z yourd137mzmhow.example.net
NAT 68 PtAlloc [NATPBlk SiteID="5A27:876E" PostS4="198.51.100.1"
PtRg="2048-2111" PtRg="4096-4159"]
Character count: about 155.
5.3.4. Address Exhaustion Event
As indicated in Table 1, the address exhaustion event is indicated by
MSG-ID set to "AddrEx". The associated SD-ELEMENT is tagged by SD-ID
"NATAddrEx". The contents of the NATAddrEx SD-ELEMENT are shown in
Table 6. The requirements for these contents are derived from the
description in Section 3.4.
+------------+---------------+-------------+
| PARAM-NAME | Description | Requirement |
+------------+---------------+-------------+
| DevTyp | Section 5.2.3 | OPTIONAL |
| DevID | Section 5.2.2 | OPTIONAL |
| APoolId | Section 5.2.1 | MANDATORY |
+------------+---------------+-------------+
Table 6: Contents Of the SD-ELEMENT Section For Logging the Address
Exhaustion Event
The example shows this event being reported by a DS-Lite AFTR. Note
the critical priority indication at the beginning of the log. As
with the session example, we assume off-board log generation.
<82>1 2013-05-07T22:14:15.03Z record.example.net NAT 5063
AddrEx [NATAddrEx DevID="bgw211.example.net" APoolId="2"]
Character count: about 120.
5.3.5. NAT Port Exhaustion
As indicated in Table 1, the port exhaustion event is indicated by
MSG-ID set to "PortEx". The associated SD-ELEMENT is tagged by SD-ID
"NATPEx". The contents of the NATPEx SD-ELEMENT are shown in Table
7. The requirements for these contents are derived from the
description in Section 3.5.
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+------------+----------------+-------------+
| PARAM-NAME | Description | Requirement |
+------------+----------------+-------------+
| DevTyp | Section 5.2.3 | OPTIONAL |
| DevID | Section 5.2.2 | OPTIONAL |
| PostS4 | Section 5.2.4 | MANDATORY |
| Proto | Section 5.2.7 | MANDATORY |
+------------+----------------+-------------+
Table 7: Contents Of the SD-ELEMENT Section For Logging the Port
Exhaustion Event
The example is straightforward. Note the warning priority indication
at the beginning of the log.
<84>1 2013-05-07T22:14:15.03Z cerberus.example.com NAT 5063
PortEx [NATPEx PostS4="198.51.100.1" Proto="6"]
Character count: about 110.
5.3.6. Quota Exceeded
As indicated in Table 1, the quota exceeded event is indicated by
MSG-ID set to "Quota". The associated SD-ELEMENT is tagged by SD-ID
"NATQEx". The contents of the NATQEx SD-ELEMENT are shown in Table
8. The requirements for these contents are derived from the
description in Section 3.6.
+------------+----------------+-------------+
| PARAM-NAME | Description | Requirement |
+------------+----------------+-------------+
| DevTyp | Section 5.2.3 | OPTIONAL |
| DevID | Section 5.2.2 | OPTIONAL |
| SScop | Section 5.2.12 | MANDATORY |
| PScop | Section 5.2.8 | MANDATORY |
| SiteID | Section 5.2.11 | OPTIONAL |
| VLANid | Section 5.2.14 | OPTIONAL |
| VRFid | Section 5.2.15 | OPTIONAL |
+------------+----------------+-------------+
Table 8: Contents Of the SD-ELEMENT Section For Logging the Quota
Exceeded Event
Example 1: limit on TCP sessions for a specific user site reached at
an AFTR with off-board log generation.
<85>1 2013-05-07T22:14:15.03Z record.example.net NAT 5063
Quota [NATQEx DevID="bgw211.example.net" SScop="S" PScop="6"
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SiteID="A2E0:62"]
Character count: about 135.
Example 2: global limit on number of sessions for all subscribers
served by the same VLAN.
<85>1 2013-05-07T15:27:49.603-04:00 cerberus.example.com
NAT 175 Quota [NATQEx SScop="M" PScop="*" VLANid="1246"]
Character count: about 115.
Example 3: limit on total number of sessions for TCP.
<85>1 2013-05-07T15:27:49.603-04:00 cerberus.example.com
NAT 175 Quota [NATQEx SScop="*" PScop="6"]
Character count: about 100.
5.3.7. Invalid Port Detected
As indicated in Table 1, the invalid port detected event is indicated
by MSG-ID set to "InvPort". The associated SD-ELEMENT is tagged by
SD-ID "NATInvP". The contents of the NATInvP SD-ELEMENT are shown in
Table 9. The requirements for these contents are derived from the
description in Section 3.7.
+------------+----------------+-------------+
| PARAM-NAME | Description | Requirement |
+------------+----------------+-------------+
| DevID | Section 5.2.2 | OPTIONAL |
| SiteID | Section 5.2.11 | MANDATORY |
| PSID | Section 5.2.9 | MANDATORY |
+------------+----------------+-------------+
Table 9: Contents Of the SD-ELEMENT Section For Logging the Invalid
Port detected Event
Example: Lightweight 4over6 BR configured with PSID 15 for the given
subscriber site.
<83>1 2013-05-07T15:27:49.603Z yourd137mzmhow.example.net
NAT 68 InvPort [NATInvP SiteID="5A27:876E" PSID="15"]
Character count: about 110.
6. IANA Considerations
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This document requests IANA to make the following assignments to the
SYSLOG Structured Data ID Values registry. RFCxxxx refers to the
present document when approved.
+----------------+------------------+-----------------+-------------+
| Structured | Structured Data | Required or | Reference |
| Data ID | Parameter | Optional | |
+----------------+------------------+-----------------+-------------+
| NATsess | | OPTIONAL | RFCxxxx |
| | DevTyp | OPTIONAL | RFCxxxx |
| | DevID | OPTIONAL | RFCxxxx |
| | SiteID | MANDATORY | RFCxxxx |
| | PostS4 | MANDATORY | RFCxxxx |
| | Proto | MANDATORY | RFCxxxx |
| | PreSPt | MANDATORY | RFCxxxx |
| | PostSPt | MANDATORY | RFCxxxx |
| | TrigR | OPTIONAL | RFCxxxx |
| ---- | ---- | ---- | ---- |
| NATBind | | OPTIONAL | RFCxxxx |
| | DevTyp | OPTIONAL | RFCxxxx |
| | DevID | OPTIONAL | RFCxxxx |
| | SiteID | MANDATORY | RFCxxxx |
| | PostS4 | MANDATORY | RFCxxxx |
| ---- | ---- | ---- | ---- |
| NATPBlk | | OPTIONAL | RFCxxxx |
| | DevTyp | OPTIONAL | RFCxxxx |
| | DevID | OPTIONAL | RFCxxxx |
| | SiteID | MANDATORY | RFCxxxx |
| | PostS4 | MANDATORY | RFCxxxx |
| | PtRg | MANDATORY | RFCxxxx |
| ---- | ---- | ---- | ---- |
| NATAddrEx | | OPTIONAL | RFCxxxx |
| | DevTyp | OPTIONAL | RFCxxxx |
| | DevID | OPTIONAL | RFCxxxx |
| | APoolId | MANDATORY | RFCxxxx |
| ---- | ---- | ---- | ---- |
| NATPEx | | OPTIONAL | RFCxxxx |
| | DevTyp | OPTIONAL | RFCxxxx |
| | DevID | OPTIONAL | RFCxxxx |
| | PostS4 | MANDATORY | RFCxxxx |
| | Proto | MANDATORY | RFCxxxx |
| ---- | ---- | ---- | ---- |
| NATQEx | | OPTIONAL | RFCxxxx |
| | DevTyp | OPTIONAL | RFCxxxx |
| | DevID | OPTIONAL | RFCxxxx |
| | SScop | MANDATORY | RFCxxxx |
| | PScop | MANDATORY | RFCxxxx |
| | SiteID | OPTIONAL | RFCxxxx |
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| | VLANid | OPTIONAL | RFCxxxx |
| | VRFid | OPTIONAL | RFCxxxx |
| ---- | ---- | ---- | ---- |
| NATInvP | | OPTIONAL | RFCxxxx |
| | DevID | OPTIONAL | RFCxxxx |
| | SiteID | MANDATORY | RFCxxxx |
| | PSID | MANDATORY | RFCxxxx |
+----------------+------------------+-----------------+-------------+
Table 10: NAT-Related STRUCTERED-DATA Registrations
IANA is further requested to establish a new registry entitled
"syslog NAT Types" within the "syslog Parameters" registry. The
initial values for this registry are shown in Table 11. New values
may be added following the criterion of IETF Review.
+-------+--------------------------------+-----------+
| Value | Description | Reference |
+-------+--------------------------------+-----------+
| 44 | NAT44 | RFCxxxx |
| 64 | NAT64 | RFCxxxx |
| AFTR | DS-Lite AFTR [RFC6333] | RFCxxxx |
| BR | Lightweight 4over6 or MAP-E BR | RFCxxxx |
+-------+--------------------------------+-----------+
Table 11: syslog NAT Type Values
7. Security Considerations
When logs are being recorded for regulatory reasons, preservation of
their integrity and authentication of their origin is essential. To
achieve this result, it is RECOMMENDED that the operator deploy
[RFC5848].
Access to the logs defined here while the reported assignments are in
force could improve an attacker's chance of hijacking a session
through port-guessing. Even after an assignment has expired, the
information in the logs SHOULD be treated as confidential, since, if
revealed, it could help an attacker trace sessions back to a
particular subscriber or subscriber location. It is therefore
RECOMMENDED that these logs be transported securely, using [RFC5425],
for example, and that they be stored securely at the collector.
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8. References
8.1. 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.
[RFC2685] Fox, B. and B. Gleeson, "Virtual Private Networks
Identifier", RFC 2685, September 1999.
[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.
[RFC5425] Miao, F., Ma, Y., and J. Salowey, "Transport Layer
Security (TLS) Transport Mapping for Syslog", RFC 5425,
March 2009.
[RFC5848] Kelsey, J., Callas, J., and A. Clemm, "Signed Syslog
Messages", RFC 5848, May 2010.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, August 2010.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
[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.
8.2. Informative References
[I-D.behave-ipfix-nat-logging]
Sivakumar, S. and R. Penno, "IPFIX Information Elements
for logging NAT Events (Work in progress)", March 2013.
[I-D.pcp-port-set]
Sun, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, T.,
and S. Perreault, "Port Control Protocol (PCP) Extension
for Port Set Allocation (Work in progress)", March 2013.
[I-D.softwire-lw4over6]
Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
Farrer, "Lightweight 4over6: An Extension to the DS-Lite
Architecture (Work in progress)", April 2013.
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[I-D.softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S., and
T. Murakami, "Mapping of Address and Port with
Encapsulation (MAP) (Work in progress)", March 2013.
[I-D.softwire-public-4over6]
Cui, Y., Wu, J., Wu, P., Vautrin, O., and Y. Lee, "Public
IPv4 over IPv6 Access Network (Work in progress)",
February 2013.
[I-D.softwire-unified-cpe]
Boucadair, M. and I. Farrer, "Unified IPv4-in-IPv6
Softwire CPE (Work in progress)", March 2013.
[I-D.tsou-behave-natx4-log-reduction]
Tsou, T., Li, W., and T. Taylor, "Port Management To
Reduce Logging In Large-Scale NATs (Work in progress)",
May 2013.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, January
2001.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC5101] Claise, B., "Specification of the IP Flow Information
Export (IPFIX) Protocol for the Exchange of IP Traffic
Flow Information", RFC 5101, January 2008.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification", RFC
5969, August 2010.
[RFC6264] Jiang, S., Guo, D., and B. Carpenter, "An Incremental
Carrier-Grade NAT (CGN) for IPv6 Transition", RFC 6264,
June 2011.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
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[RFC6674] Brockners, F., Gundavelli, S., Speicher, S., and D. Ward,
"Gateway-Initiated Dual-Stack Lite Deployment", RFC 6674,
July 2012.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
[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.
Authors' Addresses
Zhonghua Chen
China Telecom
P.R. China
Email: 18918588897@189.cn
Cathy Zhou
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
Email: cathy.zhou@huawei.com
Tina Tsou
Huawei Technologies (USA)
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1 408 330 4424
Email: tina.tsou.zouting@huawei.com
T. Taylor
Huawei Technologies
Ottawa
Canada
Email: tom.taylor.stds@gmail.com
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