D-Link DGS-6600-48TS Configuration Guide - Page 286

Volume 4 - Layer 3 Configurations Chapter Overview Automatic 6to4 Tunnel RFC 3056, "Connection of IPv6 Domains via IPv4 Clouds," specifies a mechanism for IPv6 sites to communicate with each other over the IPv4 network without explicit tunnel setup. This mechanism is called 6to4. The wide area IPv4 network is treated as a unicast point-to-point link layer, and the native IPv6 domains communicate via 6to4 routers, also referred to as 6to4 gateways. The IPv6 packets are encapsulated in IPv4 at the 6to4 gateway. At least one globally unique IPv4 unicast address is required for this configuration. The IANA has assigned a special prefix for the 6to4 scheme: 2002::/16 The key difference between automatic 6to4 tunnels and manually configured tunnels is that the tunnel is not pointto-point; it is point-to-multipoint. In automatic 6to4 tunnels, routers are not configured in pairs. The IPv4 address embedded in the IPv6 address is used to find the other end of the automatic tunnel. An automatic 6to4 tunnel may be configured on a border router in an isolated IPv6 network, which creates a tunnel on a per-packet basis to a border router in another IPv6 network over an IPv4 infrastructure. The tunnel destination is determined by the IPv4 address of the border router extracted from the IPv6 address that starts with the prefix 2002::/16, where the format is 2002: IPv4-address::/48. If tunnel interface has been configured tunnel destination address, it can't configure the tunnel type to 6to4 or ISATAP tunnel mode. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks. The simplest deployment scenario for 6to4 tunnels is to interconnect multiple IPv6 sites, each of which has at least one connection to a shared IPv4 network. This IPv4 network could be the global Internet or a corporate backbone. The key requirement is that each site has a globally unique IPv4 address. As with other tunnel mechanisms, appropriate entries in a Domain Name System (DNS) that map between hostnames and IP addresses for both IPv4 and IPv6 allow the applications to choose the required address. ISATAP Tunnels The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) is designed to provide IPv6 connectivity for dualstack nodes over an IPv4-based network. It treats the IPv4 network as one large link-layer network and allows those dual-stack nodes to automatically tunnel between themselves. You can use this automatic tunneling mechanism regardless of whether you have global or private IPv4 addresses. ISATAP addresses embed an IPv4 address in the EUI-64 interface identifier. The ISATAP router provides standard router advertisement network configuration support for the ISATAP site. This feature allows clients to automatically configure themselves. ISATAP uses a well-defined IPv6 address format composed of any unicast IPv6 prefix (/64), which can be link local, or global (including 6to4 prefixes), enabling IPv6 routing locally or on the Internet. The IPv4 address is encoded in the last 32 bits of the IPv6 address, enabling automatic IPv6-in-IPv4 tunneling. ISATAP uses unicast addresses that include a 64-bit IPv6 prefix and a 64-bit interface identifier. When the IPv4 address is known to be globally unique, the first 32bits of interface identifier is 0200:5EFE; otherwise is 0000:5EFE. The interface identifier is created in modified EUI-64 format. Table 1 describes an ISATAP address format. Table 29-1 64 Bits (prefix) 32 Bits (first 32bits of interface identifier) 32 Bits (last 32bits of interface identifier) link local or global IPv6 unicast prefix 0200:5EFE (global IPv4) 0000:5EFE (private IPv4) IPv4 address of the ISATAP link DGS-6600 Configuration Guide 286