HP-UX IPv6 Transport Administrator's Guide for TOUR 1.0

IPv6 Software and Interface Technology

Migrating from IPv4 to IPv6

Chapter 7 69

Host-to-Router IPv6/IPv4 hosts can tunnel IPv6 packets to an intermediary IPv6/IPv4

router that is reachable via an IPv4 infrastructure. This type of tunnel

spans the ﬁrst segment of the packet’s end-to-end path.

Host-to-Host IPv6/IPv4 hosts that are interconnected by an IPv4 infrastructure can

tunnel IPv6 packets between themselves. In this case, the tunnel spans

the entire end-to-end path that the packet takes.

Router-to-Host IPv6/IPv4 routers can tunnel IPv6 packets to their ﬁnal destination

IPv6/IPv4 host. This tunnel spans only the last segment of the

end-to-end path.

Conﬁgured Tunneling

Tunneling techniques are classiﬁed by the way the encapsulating node

determines the address of the node at the end of the tunnel. In

router-to-router and host-to-router tunneling methods, the IPv6 packet

is tunneled to a router. The tunnel endpoint is an intermediary router.

The intermediary router decapsulates the IPv6 packet, then forwards it

to its ﬁnal destination. When tunneling to a router, the tunnel endpoint

differs from the tunneled packet’s destination. So the addresses in the

tunneled IPv6 packet do not provide the IPv4 address of the tunnel

endpoint. Instead, the node performing the tunneling provides

conﬁguration information that determines the tunnel endpoint address.

This type of tunneling is called “conﬁgured tunneling.”

Automatic Tunneling

In the host-to-host and router-to-host tunneling methods, the IPv6

packet is tunneled all the way to its ﬁnal destination. The tunnel

endpoint is the node to which the IPv6 packet is addressed. Because the

tunnel endpoint is the IPv6 packet’s destination, the IPv6 packet’s

destination address determines the tunnel endpoint: if that address is an

IPv4-compatible IPv6 address, then the low-order 32-bits hold the

destination node’s IPv4 address. That can be used as the tunnel endpoint

address. This technique avoids the need to explicitly conﬁgure the tunnel

endpoint address. Deriving the tunnel endpoint address from the

embedded IPv4 address of the packet’s IPv6 address is called “automatic

tunneling.”