# Ipv6

# IPv6 Support

Ocamlnet supports IPv6 if the Ocaml runtime detects that IPv6 is available on the OS. For Win32 the Ocaml runtime has no IPv6 support.

## String-processing functions

The `Neturl` module can parse URLs containing IPv6 addresses, e.g. `http://[fe80::224:7eff:fedf:59ff]/path`. The address must be included in square brackets, following common Internet standards. These square brackets remain in place if the host part of the URL is extracted from the URL with `Neturl.url_host`. Note that `Unix.inet_addr_of_string` cannot process such brackets. Because of this, another function `Neturl.url_addr` has been added which returns the IP address directly.

For simple host/port pairs like `localhost:3128` another abstraction has been added, `Netsockaddr`. With `Netsockaddr.socksymbol_of_string` one can parse such pairs, and IPv6 addresses are supported. Again, these addresses need to be enclosed in square brackets.

## Protocols

The protocol interpreters for HTTP, FTP, and SOCKS have been carefully reviewed, and the necessary changes have been done.

The implementations for SMTP, POP, and the web connectors do not contain IP addresses (or are uncritical).

## Name service

The central name service module is now `Uq_resolver`. The name resolver is now pluggable, and there are two versions:

- `Uq_resolver.default_resolver` bases on `gethostbyname`, and is typically IPv4-only (but this is OS-dependent).
- `Uq_resolver.gai_resolver` bases on `getaddrinfo`, and supports both IPv4 and IPv6. One can set which address types are enabled. `getaddrinfo` may not be available on all platforms, but it always available for platforms supporting IPv6.

So, one has to change the default resolver to `gai_resolver` in order to enable IPv6 name lookups:

    Uq_resolver.set_current_resolver (Uq_resolver.gai_resolver())

It is OS-depended what else needs to be done to enable IPv6. For example, on Linux one needs

- a kernel with IPv6 support, and
- at least one network interface with a global IPv6 address (i.e. other than the fe80:* addresses)