IPv4 from home network to IPv6 Internet

AS. This simple ALG does not ‘understand’ the FTP protocol and can only forward it to another proxy that does. In our case, it forwards all FTP connections to a single central ftp proxy on a dual-stack machine located at the Telenor Research Lab. HTTP(S) traffic is handled directly by the www6to4 proxy itself. A more complex proxy could be developed or used that does understand ftp itself. However, the main advantage of www6to4 is its extremely small size, its simplicity of configuration and it has no complicated failure modes. As it is installed on each home gateway, these are important considerations.

In addition, transport level relays are used to translate connections for specific applications between specific source IPv4 address and IPv6 destination address. These relays are configured statically in each home gateway on user request. These relays are used mostly to allow IPv4-only email clients to connect to specific (IPv6) POP, IMAP or SMTP servers.

IPv4 from home network to IPv6 Internet

There is no direct IPv4 connectivity from the home network to the IPv4 Internet, and no network or transport layer translators are available currently for IPv4 to IPv6 translation. For this traffic two translations are required. First, as already explained the traffic is translated into IPv6 and routed to the main networking server. There it is again translated into IPv4 as described above.

IPv4 from Internet to IPv6 service at home

Support for this has been in a rather ad-hoc manner. Those who have servers at home need to give notice, and by means of 6tunnel (which is a Transport Relay Translator) incoming connections are then forwarded over IPv6 to the server on the home network. It works by reserving an address/port pair for each service on a dual-stack machine at the ISP. That is, the port is used to differentiate between the different sites (home networks) on the inside. This is not an elegant solution, but it works for simple protocols such as HTTP (not for FTP for example). There are obvious problems related to DNS since the target (where the service runs) and the relay do not have the same DNS entry (reverse lookup mismatch). There has been very little traffic over this mechanism and it is available mostly for completeness.

An alternative approach is to use the ALG proxy support (in apache 2, for example) to relay connections from the ISP to servers at the home networks. We have successfully tested this approach (although we inadvertently created a spam-relay for awhile due to inappropriate access control), but did not use it extensively.

IPv4 from Internet to IPv4 service at home

IPv4-to-IPv4 traffic is dealt with in the same manner as above, but with an additional translator running on the home gateway performing the translation from IPv6 to IPv4.

IPv6 from Internet to IPv4 service at home

This is dealt with by the same Transport Relay Translator discussed above.

IPv6 from Internet to IPv6 service at home

No special action is needed.