?– Requires dual-stack routers. This process enables the connection of IPv6 islands
without the need to also convert an intermediary network to IPv6. Tunneling presents
these two issues:
??” The maximum transmission unit (MTU) is effectively decreased by 20
octets if the IPv4 header does not contain an optional ?¬?eld.
??” A tunneled network is often dif?¬?cult to troubleshoot. Tunneling is an
intermediate integration and transition technique that should not be
considered a ?¬?nal solution. A native IPv6 architecture should be the
ultimate goal.
In a manually con?¬?gured tunnel, you con?¬?gure the IPv4 and IPv6 addresses statically on
the routers at each end of the tunnel. These end routers must be dual stacked, and the
con?¬?guration cannot change dynamically as network and routing needs change. You must
also properly set up routing to forward a packet between the two IPv6 networks.
Figure 7-17 illustrates the requirements for IPv6 tunnels.
Figure 7-17 IPv6 Tunnel Requirements
Dual-Stack
Router
Dual-Stack
Router
IPv6 Host IPv6 Host
IPv6
Network
IPv6
Network
IPv6 Header IPv6 Data IPv6 Header IPv6 Data
IPv4 Header IPv6 Header
Tunnel: IPv6-over-IPv4 Packet
IPv6 Data
IPv4
Network
IPv4
Dual-Stack
Router
Dual-Stack
Router
IPv4: 192.
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