Common Requirements for Carrier-Grade NATs (CGNs)
RFC 6888
| Document | Type |
RFC - Best Current Practice
(April 2013; No errata)
Updates RFC 4787
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Replaces | draft-nishitani-cgn | ||
| Stream | IETF | ||
| Formats | plain text pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | WG Document | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 6888 (Best Current Practice) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Martin Stiemerling | ||
| IESG note | Dan Wing (dwing@cisco.com) is the document shepherd. | ||
| Send notices to | (None) | ||
Internet Engineering Task Force (IETF) S. Perreault, Ed.
Request for Comments: 6888 Viagenie
BCP: 127 I. Yamagata
Updates: 4787 S. Miyakawa
Category: Best Current Practice NTT Communications
ISSN: 2070-1721 A. Nakagawa
Japan Internet Exchange (JPIX)
H. Ashida
Cisco Systems
April 2013
Common Requirements for Carrier-Grade NATs (CGNs)
Abstract
This document defines common requirements for Carrier-Grade NATs
(CGNs). It updates RFC 4787.
Status of This Memo
This memo documents an Internet Best Current Practice.
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
BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6888.
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.
Perreault, et al. Best Current Practice [Page 1]
RFC 6888 CGN Requirements April 2013
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements for CGNs . . . . . . . . . . . . . . . . . . . 4
4. Logging . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Port Allocation Scheme . . . . . . . . . . . . . . . . . . . 11
6. Deployment Considerations . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . 12
9.2. Informative Reference . . . . . . . . . . . . . . . . . 13
1. Introduction
With the shortage of IPv4 addresses, it is expected that more
Internet Service Providers (ISPs) may want to provide a service where
a public IPv4 address would be shared by many subscribers. Each
subscriber is assigned a private address, and a Network Address
Translator (NAT) [RFC2663] situated in the ISP's network translates
the traffic between private and public addresses. When a second IPv4
NAT is located at the customer edge, this results in two layers of
NAT.
This service can conceivably be offered alongside others, such as
IPv6 services or regular IPv4 service assigning public addresses to
subscribers. Some ISPs started offering such a service long before
there was a shortage of IPv4 addresses, showing that there are
driving forces other than the shortage of IPv4 addresses. One
approach to CGN deployment is described in [RFC6264].
This document describes behavior that is required of those multi-
subscriber NATs for interoperability. It is not an IETF endorsement
of CGNs or a real specification for CGNs; rather, it is just a
minimal set of requirements that will increase the likelihood of
applications working across CGNs.
Because subscribers do not receive unique IPv4 addresses, Carrier-
Grade NATs introduce substantial limitations in communications
between subscribers and with the rest of the Internet. In
particular, it is considerably more involved to establish proxy
functionality at the border between internal and external realms.
Some applications may require substantial enhancements, while some
others may not function at all in such an environment. Please see
"Issues with IP Address Sharing" [RFC6269] for details.
Perreault, et al. Best Current Practice [Page 2]
RFC 6888 CGN Requirements April 2013
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