4.1.e Describe IPv6 tunneling techniques

4.1.e [i] 6in4, 6to4

6in4 is an Internet transition mechanism for migrating from Internet Protocol version 4 (IPv4) to IPv6. 6in4 uses tunneling to encapsulate IPv6 traffic over explicitly-configured IPv4 links as defined in RFC 4213 . The 6in4 traffic is sent over the IPv4 Internet inside IPv4 packets whose IP headers have the IP protocol number set to 41. This protocol number is specifically designated for IPv6 encapsulation. In 6in4, the IPv4 packet header is immediately followed by the IPv6 packet being carried. This means that the encapsulation overhead is simply the size of the IPv4 header of 20 bytes. With an Ethernet Maximum Transmission Unit (MTU) of 1500 bytes, one can thus send IPv6 packets of 1480 bytes without fragmentation. 6in4 tunneling is also referred to as proto-41 static because the endpoints are configured statically.

6to4 Tunneling is one of the IPv6 translation mechanism which encapsulates the IPv6 packets into IPv4 which allows remote IPv6 networks to communicate across the IPv4 infrastructure( core network or Internet). The main difference between the manual tunnels and automatic 6to4 tunnels is that the tunnel is not point-to-point but it is point-to-multipoint. In automatic 6to4 tunnels, the IPv4 infrastructure is treated as a virtual non -broadcast multi-access (NBMA) link routers are not configured as point-to-point. The IPv4 address embedded in the IPv6 address is used to find the other end of the automatic tunnel.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 4655-4664).  . Kindle Edition.