IP Fragmentation: is an Internet Protocol (IP) process that breaks packets into smaller pieces (fragments), so that the resulting pieces can pass through a link with a smaller maximum transmission unit (MTU) than the original packet size. The fragments are reassembled by the receiving host.
The main methods for ipv4 to ipv6 transition are Manual, Teredo, 6 to 4, ISATAP Tunnelling, and NAT-PT. GRE is another tunnelling technology that is similar to the other tunnelling technologies, and used for IPv4 to IPv6 tunnelling and vice versa.
GRE (Generic Routing Encapsulation): IPv6 traffic can be carried over IPv4 GRE tunnels using the standard GRE tunneling technique. The tunnels are not tied to a specific passenger or transport protocol, but in this case, carry IPv6 as the passenger protocol with the GRE as the carrier protocol and IPv4 or IPv6 as the transport protocol. The primary use of GRE tunnels is for stable connections that require regular secure communication between two edge routers or between an edge router and an end system. The edge routers and the end systems must be dual-stack implementations.
NAT-PT: The term NAT-PT stands for Network Address Translation and Protocol Translation. NAT refers to translation of an IPv4 address into an IPv6 address and vice-versa and PT stands for the translation of the IPv4 packet into a semantically equivalent IPv6 packet and vice-versa. NAT-PT allows native IPv6 hosts and applications to communicate with native IPv4 hosts and applications, and vice-versa. A NAT-PT device resides at the boundary between an IPv6 and IPv4 network. Using a protocol translator between IPv6 and IPv4 allows direct communication between hosts speaking a different network protocol. One of the benefits of NAT-PT is that no changes are required to existing hosts, because all the NAT-PT configurations are performed at the NAT-PT router. Customers with existing stable IPv4 networks can introduce an IPv6 network and use NAT-PT to allow communication without disrupting the existing network. NAT-PT is not recommended for a scenario in which an IPv6-only network is trying to communicate to another IPv6-only network via an IPv4 backbone or vice versa .
6 to 4: 6to4 enables dual-stack devices to transmit IPv6 traffic across an IPv4 backbone via 6to4 relay servers without the need to manually configure tunnels. Similar to ISATAP, the tunneled IPv6 traffic is encapsulated in IPv4 protocol packets on the IPv4 network. 6to4 may be used by an individual host, or by a local IPv6 network.
ISATAP: ISATAP (Intra-Site Automatic Tunnel Addressing Protocol) is an IPv6 transition mechanism meant to transmit IPv6 packets between IPv6 and IPv4 hosts. ISATAP works by mapping an IPv4 address into the IPv6 address and requires an ISATAP gateway on the IPv6 Internet and the IPv4 Intranet. Its addresses are formatted in a very unique way. Here is an example of an ISATAP address: 2002:9D36:1:2:0:5EFE:192.168.12.9
If you look closely, you will notice that the first portion of the address, 2002:9D36:1:2:0:5EFE: is formatted like a typical IPv6 address. The subsequent portion of the address looks like an IPv4 address - 192.168.12.9. The format of this address provides some key information:
1) It is a valid IPv6 address that can be used for IPv6 communication
2) The presence of the IPv4 address indicates the IPv4 information that will be used to shuttle the IPv6 traffic over the IPv4 network.
Teredo: is a transition technology that gives full IPv6 connectivity for IPv6-capable hosts which are on the IPv4 Internet but which have no direct native connection to an IPv6 network. Compared to other similar protocols its distinguishing feature is that it is able to perform its function even from behind network address translation (NAT) devices such as home routers.
Following are true when an ipv6 enabled router running 6 to 4 tunnel must transmit a packet to a remote IPv6 destination
Unicast 6to4 addresses (2002::/16) - IPv6 uses 6to4 addresses to communicate between two IPv6/IPv4 nodes over the IPv4 Internet. A 6to4 address combines the prefix 2002::/16 with the 32 bits of the public IPv4 address of the node to create a 48-bit prefix - 2002:WWXX:YYZZ::/48, where WWXX:YYZZ is the colon-hexadecimal representation of w.x.y.z, a public IPv4 address. Therefore, the IPv4 address 188.8.131.52 translates into a 6to4 address prefix of 2002:9F3C:5B77 ::/48.