INET6(4)

INET6(4) | Device Drivers Manual | INET6(4)

# NAME

`inet6` —
Internet protocol version 6 family

# SYNOPSIS

`#include <sys/types.h>`
`#include <netinet/in.h>`

# DESCRIPTION

The `inet6` family is an updated version of inet(4) family. While inet(4) implements Internet Protocol version 4, `inet6` implements Internet Protocol version 6.

`inet6` is a collection of protocols layered atop the Internet Protocol version 6 (IPv6) transport layer, and using the IPv6 address format. The `inet6` family provides protocol support for the `SOCK_STREAM`, `SOCK_DGRAM`, and `SOCK_RAW` socket types; the `SOCK_RAW` interface provides access to the IPv6 protocol.

# ADDRESSING

IPv6 addresses are 16 byte quantities, stored in network standard byteorder. The include file `<netinet/in.h>` defines this address as a discriminated union.

Sockets bound to the `inet6` family use the following addressing structure:

    struct sockaddr_in6 {
    	uint8_t		sin6_len;
    	sa_family_t	sin6_family;
    	in_port_t	sin6_port;
    	uint32_t	sin6_flowinfo;
    	struct in6_addr	sin6_addr;
    	uint32_t	sin6_scope_id;
    };

Sockets may be created with the local address “`::`” (which is equal to IPv6 address `0:0:0:0:0:0:0:0`) to effect “wildcard” matching on incoming messages.

The IPv6 specification defines scoped addresses, like link-local or site-local addresses. A scoped address is ambiguous to the kernel, if it is specified without a scope identifier. To manipulate scoped addresses properly from the userland, programs must use the advanced API defined in RFC 2292. A compact description of the advanced API is available in ip6(4). If a scoped address is specified without an explicit scope, the kernel may raise an error. Note that scoped addresses are not for daily use at this moment, both from a specification and an implementation point of view.

The KAME implementation supports an extended numeric IPv6 address notation for link-local addresses, like “`fe80::1%de0`” to specify “`fe80::1` on `de0` interface”. This notation is supported by getaddrinfo(3) and getnameinfo(3). Some of normal userland programs, such as telnet(1) or ftp(1), are able to use this notation. With special programs like ping6(8), you can specify the outgoing interface by an extra command line option to disambiguate scoped addresses.

Scoped addresses are handled specially in the kernel. In kernel structures like routing tables or interface structures, a scoped address will have its interface index embedded into the address. Therefore, the address in some kernel structures is not the same as that on the wire. The embedded index will become visible through a `PF_ROUTE` socket, kernel memory accesses via kvm(3) and on some other occasions. HOWEVER, users should never use the embedded form. For details please consult http://www.kame.net/dev/cvsweb2.cgi/kame/IMPLEMENTATION. Note that the above URL describes the situation with the latest KAME tree, not the NetBSD tree.

# PROTOCOLS

The `inet6` family comprises the IPv6 network protocol, Internet Control Message Protocol version 6 (ICMPv6), Transmission Control Protocol (TCP), and User Datagram Protocol (UDP). TCP is used to support the `SOCK_STREAM` abstraction while UDP is used to support the `SOCK_DGRAM` abstraction. Note that TCP and UDP are common to inet(4) and `inet6`. A raw interface to IPv6 is available by creating an Internet socket of type `SOCK_RAW`. The ICMPv6 message protocol is accessible from a raw socket.

## Interaction between IPv4/v6 sockets

By default, NetBSD does not route IPv4 traffic to `AF_INET6` sockets. The default behavior intentionally violates RFC 2553 for security reasons. Listen to two sockets if you want to accept both IPv4 and IPv6 traffic. IPv4 traffic may be routed with certain per-socket/per-node configuration, however, it is not recommended to do so. Consult ip6(4) for details.

The behavior of `AF_INET6` TCP/UDP socket is documented in RFC 2553. Basically, it says this:

- A specific bind on an `AF_INET6` socket (bind(2) with an address specified) should accept IPv6 traffic to that address only.
- If you perform a wildcard bind on an `AF_INET6` socket (bind(2) to IPv6 address `::`), and there is no wildcard bind `AF_INET` socket on that TCP/UDP port, IPv6 traffic as well as IPv4 traffic should be routed to that `AF_INET6` socket. IPv4 traffic should be seen as if it came from an IPv6 address like `::ffff:10.1.1.1`. This is called an IPv4 mapped address.
- If there are both a wildcard bind `AF_INET` socket and a wildcard bind `AF_INET6` socket on one TCP/UDP port, they should behave separately. IPv4 traffic should be routed to the `AF_INET` socket and IPv6 should be routed to the `AF_INET6` socket.

However, RFC 2553 does not define the ordering constraint between calls to bind(2), nor how IPv4 TCP/UDP port numbers and IPv6 TCP/UDP port numbers relate to each other (should they be integrated or separated). Implemented behavior is very different from kernel to kernel. Therefore, it is unwise to rely too much upon the behavior of `AF_INET6` wildcard bind sockets. It is recommended to listen to two sockets, one for `AF_INET` and another for `AF_INET6`, when you would like to accept both IPv4 and IPv6 traffic.

It should also be noted that malicious parties can take advantage of the complexity presented above, and are able to bypass access control, if the target node routes IPv4 traffic to `AF_INET6` socket. Users are advised to take care handling connections from IPv4 mapped address to `AF_INET6` sockets.

# SEE ALSO

ioctl(2), socket(2), sysctl(3), icmp6(4), intro(4), ip6(4), tcp(4), udp(4)

Qing Li, Tatuya Jinmei, and Keiichi Shima, IPv6 Core Protocols Implementation, Morgan Kaufmann, 2006.

Qing Li, Tatuya Jinmei, and Keiichi Shima, IPv6 Advanced Protocols Implementation, Morgan Kaufmann, 2007.

# STANDARDS

Tatuya Jinmei and Atsushi Onoe, An Extension of Format for IPv6 Scoped Addresses, internet draft, draft-ietf-ipngwg-scopedaddr-format-02.txt, June 2000, work in progress material.

# HISTORY

The `inet6` protocol interfaces are defined in RFC 2553 and RFC 2292. The implementation described herein appeared in the WIDE/KAME project.

# BUGS

The IPv6 support is subject to change as the Internet protocols develop. Users should not depend on details of the current implementation, but rather the services exported.

Users are suggested to implement “version independent” code as much as possible, as you will need to support both inet(4) and `inet6`.

March 10, 2010 | NetBSD 10.1