System Administration Guide: IP Services

6to4 Automatic Tunnels

Oracle Solaris includes 6to4 tunnels as a preferred interim method for making the transition from IPv4 to IPv6 addressing. 6to4 tunnels enable isolated IPv6 sites to communicate across an automatic tunnel over an IPv4 network that does not support IPv6. To use 6to4 tunnels, you must configure a boundary router on your IPv6 network as one endpoint of the 6to4 automatic tunnel. Thereafter, the 6to4 router can participate in a tunnel to another 6to4 site, or, if required, to a native IPv6, non-6to4 site.

This section provides reference materials on the following 6to4 topics:

The following table describes additional tasks to configure 6to4 tunnels and the resources to obtain additional useful information.

Task or Detail 

For Information 

Tasks for configuring a 6to4 tunnel 

How to Configure a 6to4 Tunnel

6to4-related RFC 

RFC 3056, "Connection of IPv6 Domains via IPv4 Clouds"

Detailed information about the 6to4relay command, which enables support for tunnels to a 6to4 relay router


6to4 security issues 

Security Considerations for 6to4

Topology of a 6to4 Tunnel

A 6to4 tunnel provides IPv6 connectivity to all 6to4 sites everywhere. Likewise, the tunnel also functions a link to all IPv6 sites, including the native IPv6 internet, provided that the tunnel is configured to forward to a relay router. The following figure shows how a 6to4 tunnel provides this connectivity between 6to4 sites.

Figure 11–6 Tunnel Between Two 6to4 Sites

The figure shows a 6to4 tunnel, which is described in
the following context.

The figure depicts two isolated 6to4 networks, Site A and Site B. Each site has configured a router with an external connection to an IPv4 network. A 6to4 tunnel across the IPv4 network provides a connection to link 6to4 sites.

Before an IPv6 site can become a 6to4 site, you must configure at least one router interface for 6to4 support. This interface must provide the external connection to the IPv4 network. The address that you configure on qfe0 must be globally unique. In this figure, boundary Router A's interface qfe0 connects Site A to the IPv4 network. Interface qfe0 must already be configured with an IPv4 address before you can configure qfe0 as a 6to4 pseudo-interface.

In the figure, 6to4 Site A is composed of two subnets, which are connected to interfaces hme0 and hme1 on Router A. All IPv6 hosts on either subnet of Site A automatically reconfigure with 6to4-derived addresses upon receipt of the advertisement from Router A.

Site B is another isolated 6to4 site. To correctly receive traffic from Site A, a boundary router on Site B must be configured for 6to4 support. Otherwise, packets that the router receives from Site A are not recognized and are then dropped.

Packet Flow Through the 6to4 Tunnel

This section describes the flow of packets from a host at one 6to4 site to a host at a remote 6to4 site. This scenario uses the topology that is shown in Figure 11–6. Moreover, the scenario assumes that the 6to4 routers and the 6to4 hosts are already configured.

  1. A host on Subnet 1 of 6to4 Site A sends a transmission, with a host at 6to4 Site B as the destination. Each packet header has a 6to4-derived source address and 6to4-derived destination address.

  2. Site A's router encapsulates each 6to4 packet within an IPv4 header. In this process, the router sets the IPv4 destination address of the encapsulating header to Site B's router address. For each IPv6 packet that flows through the tunnel interface, the packet's IPv6 destination address also contains the IPv4 destination address. Thus, the router is able to determine the IPv4 destination address that is set on the encapsulating header. Then, the router uses standard IPv4 routing procedures to forward the packet over the IPv4 network.

  3. Any IPv4 routers that the packets encounter use the packets' IPv4 destination address for forwarding. This address is the globally unique IPv4 address of the interface on Router B, which also serves as the 6to4 pseudo-interface.

  4. Packets from Site A arrive at Router B, which decapsulates the IPv6 packets from the IPv4 header.

  5. Router B then uses the destination address in the IPv6 packet to forward the packets to the recipient host at Site B.

Considerations for Tunnels to a 6to4 Relay Router

6to4 relay routers function as endpoints for tunnels from 6to4 routers that need to communicate with native IPv6, non-6to4 networks. Relay routers are essentially bridges between the 6to4 site and native IPv6 sites. Because this solution might be insecure, by default, Oracle Solaris does not enable 6to4 relay router support. However, if your site requires such a tunnel, you can use the 6to4relay command to enable the following tunneling scenario.

Figure 11–7 Tunnel From a 6to4 Site to a 6to4 Relay Router

This figure shows a tunnel between a 6to4 router and
6to4 relay router. The following context further describes the figure.

In Figure 11–7, 6to4 Site A needs to communicate with a node at the native IPv6 Site B. The figure shows the path of traffic from Site A onto a 6to4 tunnel over an IPv4 network. The tunnel has 6to4 Router A and a 6to4 relay router as its endpoints. Beyond the 6to4 relay router is the IPv6 network, to which IPv6 Site B is connected.

Packet Flow Between a 6to4 Site and a Native IPv6 Site

This section describes the flow of packets from a 6to4 site to a native IPv6 site. This scenario uses the topology that is shown in Figure 11–7.

  1. A host on 6to4 Site A sends a transmission that specifies as the destination a host at native IPv6 Site B. Each packet header has a 6to4-derived address as its source address. The destination address is a standard IPv6 address.

  2. Site A's 6to4 router encapsulates each packet within an IPv4 header, which has the IPv4 address of the 6to4 relay router as its destination. The 6to4 router uses standard IPv4 routing procedures to forward the packet over the IPv4 network. Any IPv4 routers that the packets encounter forward the packets to the 6to4 relay router.

  3. The physically closest anycast 6to4 relay router to Site A retrieves the packets that are destined for the anycast group.

    Note –

    6to4 relay routers that are part of the 6to4 relay router anycast group have the IP address This anycast address is the default address for 6to4 relay routers. If you need to use a specific 6to4 relay router, you can override the default and specify that router's IPv4 address.

  4. The relay router decapsulates the IPv4 header from the 6to4 packets, revealing the native IPv6 destination address.

  5. The relay router then sends the now IPv6-only packets onto the IPv6 network, where the packets are ultimately retrieved by a router at Site B. The router then forwards the packets to the destination IPv6 node.