6in4
Encyclopedia
6in4 is an Internet transition mechanism for migrating from Internet Protocol version 4
(IPv4) to IPv6
. 6in4 uses tunneling
to encapsulate IPv6 traffic over explicitly-configured IPv4 links as defined in RFC 4213 (obsoletes RFC 2893 and RFC 1933). The 6in4 traffic is sent over the IPv4 Internet inside IPv4 packets whose IP headers have the IP protocol number set to 41. This protocol number is specifically designated for IPv6 encapsulation. In 6in4, the IPv4 packet header is immediately followed by the IPv6 packet being carried. This means that the encapsulation overhead is simply the size of the IPv4 header of 20 bytes. With an Ethernet Maximum Transmission Unit
(MTU) of 1500 bytes, one can thus send IPv6 packets of 1480 bytes without fragmentation. 6in4 tunneling is also referred to as proto-41 static because the endpoints are configured statically. Although 6in4 tunnels are generally manually configured, for example the utility AICCU
can configure tunnel parameters automatically after retrieving information from a Tunnel Information and Control Protocol (TIC) server.
There are similarly named methods, namely 6to4
or 6over4
, which describe a different mechanism. The method 6to4
makes use of proto-41 too, but instead of static configuration of the endpoints, the endpoint IPv4 address information is derived from the IPv6 addresses within the IPv6 packet header.
, one can in some cases still make use of the DMZ feature of a NAT router. The NAT router will then forward all incoming proto-41 packets to the configured host, thus making the tunnel work. Some NAT devices even allow transparent operation of 6in4.
can then update the endpoints, in effect making the endpoint dynamic while still using the 6in4 protocol. These kind of tunnels are generally called 'proto-41 heartbeat' tunnels.
the source IPv4 address of a tunnel endpoint and sending it to the other endpoint. This problem can partially be solved by implementing network ingress filtering or with IPsec
. Another solution is to use a secure protocol such as AYIYA or other tunneling methods that compute digital signatures for each packet thus facilitating verification of packet authenticity.
The mentioned packet injection loophole of 6in4 was exploited for a research benefit in a method called IPv6 Tunnel Discovery which allowed the researchers to discover operating IPv6 tunnels around the world.
IPv4
Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
(IPv4) to IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
. 6in4 uses tunneling
Tunneling protocol
Computer networks use a tunneling protocol when one network protocol encapsulates a different payload protocol...
to encapsulate IPv6 traffic over explicitly-configured IPv4 links as defined in RFC 4213 (obsoletes RFC 2893 and RFC 1933). The 6in4 traffic is sent over the IPv4 Internet inside IPv4 packets whose IP headers have the IP protocol number set to 41. This protocol number is specifically designated for IPv6 encapsulation. In 6in4, the IPv4 packet header is immediately followed by the IPv6 packet being carried. This means that the encapsulation overhead is simply the size of the IPv4 header of 20 bytes. With an Ethernet Maximum Transmission Unit
Maximum transmission unit
In computer networking, the maximum transmission unit of a communications protocol of a layer is the size of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a communications interface...
(MTU) of 1500 bytes, one can thus send IPv6 packets of 1480 bytes without fragmentation. 6in4 tunneling is also referred to as proto-41 static because the endpoints are configured statically. Although 6in4 tunnels are generally manually configured, for example the utility AICCU
AICCU
AICCU is a popular cross-platform utility for automatically configuring an IPv6 tunnel. It is free software available under a BSD license. The utility is originally provided for the SixXS Tunnel Broker but it can also be used by a variety of other tunnel brokers.-History and development:AICCU is...
can configure tunnel parameters automatically after retrieving information from a Tunnel Information and Control Protocol (TIC) server.
There are similarly named methods, namely 6to4
6to4
6to4 is an Internet transition mechanism for migrating from IPv4 to IPv6, a system that allows IPv6 packets to be transmitted over an IPv4 network without the need to configure explicit tunnels...
or 6over4
6over4
6over4 is an IPv6 transition mechanism meant to transmit IPv6 packets between dual-stack nodes on top of a multicast-enabled IPv4 network. IPv4 is used as a virtual data link layer on which IPv6 can be run.-How 6over4 works:...
, which describe a different mechanism. The method 6to4
6to4
6to4 is an Internet transition mechanism for migrating from IPv4 to IPv6, a system that allows IPv6 packets to be transmitted over an IPv4 network without the need to configure explicit tunnels...
makes use of proto-41 too, but instead of static configuration of the endpoints, the endpoint IPv4 address information is derived from the IPv6 addresses within the IPv6 packet header.
Network address translators (NAT)
When an endpoint of a 6in4 tunnel is behind a NATNetwork address translation
In computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....
, one can in some cases still make use of the DMZ feature of a NAT router. The NAT router will then forward all incoming proto-41 packets to the configured host, thus making the tunnel work. Some NAT devices even allow transparent operation of 6in4.
Dynamic 6in4 tunnels and heartbeat
Even though 6in4 tunnels are static in nature, with the help of for example the heartbeat protocol one can still have dynamic tunnel endpoints. The heartbeat protocol signals the other side of the tunnel with its current endpoint location. A tool such as AICCUAICCU
AICCU is a popular cross-platform utility for automatically configuring an IPv6 tunnel. It is free software available under a BSD license. The utility is originally provided for the SixXS Tunnel Broker but it can also be used by a variety of other tunnel brokers.-History and development:AICCU is...
can then update the endpoints, in effect making the endpoint dynamic while still using the 6in4 protocol. These kind of tunnels are generally called 'proto-41 heartbeat' tunnels.
Security issues
The 6in4 protocol has no security features, thus one can easily inject IPv6 packets by spoofingIP address spoofing
In computer networking, the term IP address spoofing or IP spoofing refers to the creation of Internet Protocol packets with a forged source IP address, called spoofing, with the purpose of concealing the identity of the sender or impersonating another computing system.-Background:The basic...
the source IPv4 address of a tunnel endpoint and sending it to the other endpoint. This problem can partially be solved by implementing network ingress filtering or with IPsec
IPsec
Internet Protocol Security is a protocol suite for securing Internet Protocol communications by authenticating and encrypting each IP packet of a communication session...
. Another solution is to use a secure protocol such as AYIYA or other tunneling methods that compute digital signatures for each packet thus facilitating verification of packet authenticity.
The mentioned packet injection loophole of 6in4 was exploited for a research benefit in a method called IPv6 Tunnel Discovery which allowed the researchers to discover operating IPv6 tunnels around the world.