What's The Difference Between IPv4 and IPv6

IPv4/IPv6 Coexistance

IPv4 and IPv6 subnets have and will continue to coexist even as the overall Internet moves from IPv4 to IPv6. There are a number of mechnisms in place that facilitate this. These include Stateless IP/ICMP Translation (SIIT), 6rd, NAT, tunneling and proxy server support. Many of the techniques can be deployed in firewalls and routers between IPv4 and IPv6 subnets.

SIIT uses ::/96 address and maps the 32-bit IPv4 to the lower bits of an IPv6 address. This allows direct access of IPv4 hosts by IPv6 nodes.

6rd (IPv6 rapid deployment) uses IPv6 to bridge IPv4 subnets. It tunnels IPv4 packet over IPv6. It is sometimes a service provided by ISPs.

Proxy servers with dual stacks can operate in either direction providing IPv4 access to an IPv6 server and vice versa. Proxy servers tend to be a stopgap measure since each proxy must be explicity configured.

IPv4 NAT gateways provide a mechanism for linking IPv4 devices to the IPv6 Internet. Of course, this assumes that the gateway can connect to an IPv6 network. Most of the latest commercial and consumer devices can do this but older devices are IPv4 only. In this case, an additional gateway is required so the IPv4 to IPv6 translation occurs outside a customer's premises.

Dual stack hosts are likely to be common as well. A network can carry IPv4 and IPv6 traffic at the same time. A dual stack host can communicate with either type of device as well as having its traffic routed to the outside world if appropriate. Dual stack routers can be gateways as well.

Unfortunately, mixed IPv4/IPv6 environments are fragile and many of the techniques will not work well together. Combine this with IPv4 extensions such as IPsec and other protocols and there is the possibility that connections might be made but applications will not work. The only likely combinations that will work well will be IPv4-to-IPv4 and IPv6-to-IPv6.

One issue that will have to wait for another article is IPv6 security. Because of the differences and features of IPv6, firewalls and security software need to address additional security issues that IPv4 did not. For example, tunneling solutions mentioned earlier can bring the more open IPv6 into an IPv4 network. It is possible to prevent or mitigate attacks along these lines but only if proper security configurations are used and if the hardware support this.

So what happened to IPv5? IPv5 is a designation for a variant of the Internet Stream Protocol (ST) that started back in 1979 but abandoned. Many of the features of ST are found in Multiprotocol Label Switching (MPLS) standard. IPv6 was based on IPng (IP next generation) work and IPv6 was initially called IPng version 7.

Related Resources

• American Registry for Internet Numbers (ARIN)
• Internet Engineering Task Force (IETF)