process enables you to connect the IPv6 islands without converting the entire network to IPv6. Tunneling is an integration method where an IPv6 packet is encapsulated within another protocol, such as IPv4. This method of encapsulation is IPv4 protocol 41 and has the following characteristics: Tunneling is an intermediate integration and transition technique that should not be considered a final solution. Native IPv6 architecture should be the ultimate goal.
Content 8.6 Using IPv6 and IPv4 8.6.4 Isolated Dual-Stack Host Encapsulation can be done by edge routers between hosts or between a host and a router. The example in Figure shows an isolated dual-stack host using an encapsulated tunnel to connect to the edge router of the IPv6 network. Tunneling does not work if an intermediary node between the two end points of the tunnel, such as a firewall, filters out IPv4 protocol 41, which is the IPv6-over-IPv4 encapsulation.
Content 8.6 Using IPv6 and IPv4 8.6.5 Configuring Tunneling If you are manually configuring a tunnel, you should configure both the IPv4 and IPv6 addresses statically. You should perform this configuration on the routers at each end of the tunnel. These end routers must be dual stacked, and the configuration cannot change dynamically as network and routing needs change. Routing must be set up properly to forward a packet between the two IPv6 networks. Tunnel endpoints can be unnumbered, but unnumbered endpoints make troubleshooting difficult. The IPv4 practice of saving addresses for tunnel endpoints is no longer an issue.
Content 8.6 Using IPv6 and IPv4 8.6.6 Example of a Configured Tunnel The example in Figure shows how to configure an IPv6 overlay tunnel manually. With manually configured IPv6 tunnels, an IPv6 address is configured on a tunnel interface, and manually configured IPv4 addresses are assigned to the tunnel source and the tunnel destination. The host or router at each end of a configured tunnel must support both the IPv4 and IPv6 protocol stacks.The command that enables the IPv6 overlay tunnel is tunnel mode ipv6ip. Specifically, it specifies that IPv6 is the passenger protocol and that IPv4 will be used as both the encapsulation and transport protocol. Several other automatic tunneling transition mechanisms exist, including these: Another transition mechanism is Teredo (formerly known as Shipworm). This mechanism tunnels IPv6 datagrams within IPv4 UDP. This method provides for private IPv4 address use and IPv4 NAT traversal. Web Links Implementing Tunneling in IPv6
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Content 8.6 Using IPv6 and IPv4 8.6.7 IPv6 to IPv4 Tunneling and Addresses The 6to4 tunneling method automatically establishes the connection of IPv6 islands through an IPv4 network. It applies a valid IPv6 prefix to each IPv6 island, which enables the fast deployment of IPv6 in a corporate network, without address retrieval from the ISPs or registries. The 6to4 tunneling method requires a special code on the edge routers, but the IPv6 hosts and routers inside the 6to4 site do not require new features to support 6to4. Each 6to4 site receives a /48 prefix, which is the concatenation of 0x2002 and the hexadecimal IPv4 address of the edge router. In Figure , the IPv4 address of the edge router is 192.168.99.1. As a result, the prefix of its IPv6 network is 2002:c0a8:6301::/48 because c0a86301 is the hexadecimal representation of 192.168.99.1. The IPv6 network can substitute any IP address in the space after the first 16-bit section (0x2002). When an IPv6 packet with a destination address in the range of 2002::/16 reaches the 6to4 edge router, the 6to4 edge router extracts the IPv4 address that is embedded in the 2002:: destination address (inserted between the third and sixth octets, inclusive). The 6to4 router then encapsulates the IPv6 packet in an IPv4 packet with the destination IPv4 address that was extracted from inside the IPv6 destination address. This IPv4 address represents the address of the other 6to4 edge router of the destination 6to4 site. The destination edge router decapsulates the IPv6 packet in the IPv4 packet and then forwards the native packet toward its final destination. Note
2002::/16 is the address range specifically assigned to 6to4.
Content 8.6 Using IPv6 and IPv4 8.6.8 Translation of NAT-PT For legacy equipment that will not be upgraded to IPv6 and for some deployment scenarios, techniques that can connect IPv4-only nodes on IPv6-only nodes are available. Translation is basically an extension of NAT techniques. NAT-Protocol Translation (NAT-PT) is a translation mechanism that sits between an IPv6 network and an IPv4 network. The translator translates IPv6 packets into IPv4 packets and vice versa. Static NAT-PT uses static translation rules to map one IPv6 address to one IPv4 address. IPv6 network nodes communicate with IPv4 network nodes using an IPv6 mapping of the IPv4 address configured on the NAT-PT router. Figure shows how the IPv6-only node (Node A) can communicate with the IPv4-only node (Node D) using NAT-PT. The NAT-PT device is configured to map the source IPv6 address for node A of 2001:0db8:bbbb:1::1 to the IPv4 address 192.0.2.2. NAT-PT is also configured to map the source address of IPv4 node C, 192.0.30.1 to 2001:0db8::a. When packets with a source IPv6 address of Node A are received at the NAT-PT router they are translated to have a destination address to match Node D in the IPv4-only network. NAT-PT can also be configured to match a source IPv4 address and translate the packet to an IPv6 destination address to allow an IPv4-only host communicate with an IPv6-only host. From the perspective of Node A, it is establishing a communication to another IPv6 node. And from the perspective of node D, it is establishing IPv4 communication with its correspondent. Node D requires no modification. If you have multiple IPv6-only or IPv4-only hosts that need to communicate, you may need to configure many static NAT-PT mappings. Static NAT-PT is useful when applications or servers require access to a stable IPv4 address. Accessing an external IPv4 DNS server is an example where static NAT PT can be used.
NAT-PT translations may also be mapped dynamically based on DNS queries, using a DNS application level gateway (DNS ALG). Other possible solutions are as follows:
Web Links Implementing NAT-PT for IPv6
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Content 8.7 IPv6 Lab Exercises 8.7.1 Lab 8-1 Configuring OSPF for