NAT Boxes
One of the more passionate points of discussion surrounding IPv6 involves Network Address Translation (NAT) boxes.4 A NAT box is a host on the Internet with an IP address that has behind it a network of privately addressed computers. A specific block of addresses has been set aside for private use and is not advertised by networks to the public Internet.5 Since these addresses only work internally and cannot be used to communicate on the public internet, they can be reused over and over again behind NATs.
An example of a NAT might be an off-the-shelf Wi-Fi access point that a residential user might use for home Internet access. The ISP assigns to that subscriber an IP address which is assigned to whatever computer the subscriber attaches at the end of the network. The subscriber attaches the Wi-Fi router. Behind the Wi-Fi router could be all of the computers in the house; the router assigns them IP addresses from the private IP address space. In this way, a subscriber with one public IP number can have multiple computers attached to the Internet.6 Commercial ISPs may utilize private IP numbers for their subscribers, and corporate LANs (such as the FCC internal network) may also utilize private IP addresses.1
Figure 8: An Example of a Network Address Translation2
Network operators utilize NATs for various objectives. First, NATs are used to conserve the scarce numbering resource; one public address maps to multiple private addresses. Second, NATs are also used for network management and security, creating single points of entry into networks.
After the transition to IPv6, with the dramatically increased address space, NATs would no longer be necessary in order to deal with the scarce numbering resource. It is expected that with IPv6 the use of NATs will likely decrease although it may not disappear.3
NAT boxes have drawbacks.1 As stated by the CIO Council, "[w]hile NAT has to some extent delayed the exhaustion on IPv4 address space for the short term, it complicates general application bi-directional communication."2 NAT boxes break the end-to-end nature of Internet communications, and thus interfere with some Internet applications and services, and create an impediment to innovation.3
NAT boxes may work well when traffic originates from within the private network and the NAT box can track which host to return traffic to (someone on the network requests a webpage, and the NAT box knows who to return the webpage to). NAT boxes do not work so well when the traffic originates outside the network trying to reach someone inside the network (for example, someone trying to set up a VoIP call with someone inside the network.4 Since the request from the VoIP outsider came to the NAT box IP address, the NAT box has no idea which computer inside the network the outsider is actually trying to reach). 5 NAT boxes present barriers to applications which seek to take advantage of IP address transparency. They inject non-standardized intelligence into the network, requiring application developers to conform to each non-standardized implementation.6 They require a conversion from the public address space to private address spaces, which degrade the performance of some applications.7 NATs also result in less accurate geolocation, make identification and blocking of abuse more difficult, and frustrate IP-based authentication.8
Security
IPv6 is a new network protocol which will require new training, experience, and implementations. During the transition, new vulnerabilities could be introduced, and IPv4 security devices and software may be of limited use.1 As network operators have done when introducing anything new into networks, operators will have to work with and test IPv6 implementations in order to ensure security.2
Law Enforcement
The transition to IPv6 creates concerns for law enforcement. During the transition, kludges will be employed by networks in order to conserve addresses and allow networks to keep expanding. These solutions, however, break end-to-end connectively and make it difficult to map specific IP numbers to individual end users. IP numbers may map to carrier grade NAT boxes which may have behind them many households, neighborhoods, or even towns, making it difficult to know to whom an IP address belongs.3 Law enforcement has also expressed concern that WHOIS4 for IPv6 contain accurate and useful information. ISPs may incur additional administrative burdens of having to retain records of the dynamic mapping between addresses. 5 There may also be issues with CALEA compliance. The ARIN Government Working Group has been working on these issues.6
Where to Go for More Information
A wealth of information is available concerning the IPv6 transition. To learn more, review the information at the following sources:
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Numbering Authorities
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American Registry for Internet Numbers (ARIN): IPv4/IPv6: The Bottom Line
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ARIN IPv6 Wiki
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ARIN attends many technology conferences where it provides IPv6 information
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Number Resource Organization: are::you:IPv6:ready?
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IPv6 Act Now (RIPE NCC)
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United States Government
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IPv6 Transition Guidance (CIO Council)
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Technical Infrastructure for USGv6 Adoption (NIST)
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USGv6 Profile
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USGv6 Testing Program (NIST)
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DOD Joint Interoperability Test Command IPv6
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Defense Research and Engineering Network (DREN)
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North American Network Operators' Group (NANOG) IPv6 Tutorials
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NANOG holds regular meetings which include IPv6 technical information; these meetings can be viewed online and are archived.
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IPv6 Forum
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Organization for Economic Cooperation and Development Resources on Internet Addressing: IPv4 and IPv6
Other Recent Staff Papers
Titles Can Be Downloaded at
http://www.fcc.gov/papers/
“Maximum Impact for Minimum Subsidy: Reverse Auctions for Universal Access in Chile and India,” Irene S. Wu, FCC Staff Working Paper 2, October 2010.
“Transformative Choices: A Review of 70 Years of FCC Decisions,” Sherille Ismail, FCC Staff Working Paper 1, October 2010.
“A Market-Based Approach to Establishing Licensing Rules: Licensed versus Unlicensed Use of Spectrum,” Mark Bykowsky, Mark Olson, and William Sharkey, OSP Working Paper 43, February 2008.
“Modeling the Efficiency of Spectrum Designated to License Use and Unlicensed Operations,” Mark Bykowsky, Mark Olson, and William Sharkey, OSP Working Paper 42, February 2008.
“Enhancing Spectrum's Value via Market-Informed Congestion Etiquettes,” Mark Bykowsky, Kenneth Carter, Mark Olson, and William Sharkey, OSP Working Paper 41, February 2008.
“Competition Between Cable Television and Direct Broadcast Satellite - It's More Complicated Than You Think,” Andrew S. Wise and Kiran Duwadi, Media and International Bureaus, January 2005.
“The Scarcity Rationale for Regulating Traditional Broadcasting: An Idea Whose Time Has Passed,” John W. Berresford, Media Bureau, March 2005.
“A Survival Analysis of Cable Networks,” Keith S. Brown, Media Bureau, December 2004.
"Traits of an Independent Communications Regulator: a Search for Indicators," by Irene Wu, International Bureau, June 2004.
"The Limits of Economic Regulation: The U.S. Experience," Peyton L. Wynns, International Bureau, June 2004.
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