NAME
6in4 – 6to4 tunnel of IPv6 through IPv4

SYNOPSIS
ip/6in4 [ –ag ] [ –x netmtpt ] [ local6[/mask] [ remote4 [ remote6 ] ] ]

DESCRIPTION
6in4 sets up and operates a tunnel of IPv6 traffic through an IPv4 connection.

Local6 and mask define the IPv6 address and subnet of the near end of the tunnel (mask defaults to /128 for a single–host tunnel). If local6 is missing or –, it defaults to
2002:aabb:ccdd::1/48

where aa, bb, cc and dd are the hexadecimal equivalents of the bytes a.b.c.d in this host's primary IPv4 address.

Remote4 is the IPv4 address of the far end of the tunnel (must be given explicitly for a configured tunnel, or defaults to the anycast address 192.88.99.1 for 6to4).

Remote6 is the IPv6 address of the far end of the tunnel (used as the point–to–point destination for routing, and defaults to a link–local address constructed from remote4).

6in4 forks a pair of background processes to copy packets to and from the tunnel.

Options are:
a   permit any remote IPv4 address as the far end of a tunnel. This is likely to be useful for the server side of a tunnel.
g   add a default route to the tunnel for global IPv6 addresses.
x   use the network mounted at netmtpt instead of /net.

EXAMPLES
If your primary IPv4 address is public, you can start a 6to4 tunnel simply with
ip/6in4 –g

Similarly, you can start a server for 6to4 tunnels with
ip/6in4 –ag

If you use a tunnel broker at address 5.6.7.8, configured to give you a /64 subnet with address 2001:1122:3344:5566::, you can start the tunnel with
ip/6in4 –g 2001:1122:3344:5566::/64 5.6.7.8

FILES
/net/ipmux   access to IPv6–in–IPv4 packets
/net/ipifc   packet interface to IPv6 network

SEE ALSO
bridge(3), ipmux in ip(3), linklocal in ipconfig(8)
/lib/rfc/rfc3056
/lib/rfc/rfc3068

BUGS
Needs a kernel with an ipmux driver.

The tunnel client filters addresses fairly conservatively in both directions. However it's not watertight, and may be flakey in other ways so don't put too much trust in it.

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