An IPv6 over IPv4 tunnel connects isolated IPv6 sites through an IPv4 network. Exhaustion of IPv4 addresses urgently requires IPv4 to IPv6 transition. IPv6 is incompatible with IPv4, so original IPv4 devices will need to be replaced. This solution is currently infeasible because replacement requires huge capital expenditures, and will interrupt services on the live network. IPv4 therefore needs a gradual transit to IPv6. During the earlier stages, IPv4 networks are widely deployed and IPv6 networks are isolated sites. An IPv6 over IPv4 tunnel allows IPv6 packets to be transmitted on an IPv4 network and connects IPv6 sites.