Understanding Linux Network Internals

IPv4: What's Wrong with It?

We saw in the section "IP Protocol: The Big Picture" in Chapter 18 what the main tasks are of the IP protocol. IPv4 was designed almost 25 years ago (in 1981), and given the speed with which the Internet and network services have evolved since then, the protocol is showing its age. Because IPv4 was not originally designed with today's big network topologies and commercial uses in mind, it has shown several limitations over the years. These have been only partially solved, sometimes with special extensions to the protocol (e.g., classless interdomain routing), DiffServ Code Point (DSCP) replacement to ToS, congestion notification, etc.), and other times by defining specialized external protocols such as IPsec.

Thanks to the experience gained with IPv4, the new IPv6 version of the protocol has been designed to address the known shortcomings of IPv4, taking into consideration such aspects as:

• Functionality

• Ease of configuration

• Performance

• Transition from IPv4 networks to IPv6 networks

• Security

Naturally, the committees designing the new protocol have tried to keep IPv4 and IPv6 as compatible as possible, and the transition from one to another as painless as possible. This compatibility and interaction have to be handled not only at the application layer, but also at the kernel layer.

When analyzing IPv4 packet transmission, we saw that fragmentation and options processing were the two most expensive tasks. It should not come as a surprise, therefore, that IPv6 ...