• At this point we have concluded the basic mechanics of IPv4. Still to come is a discussion of how IP routers build their forwarding tables. This turns out to be a complex topic, divided into routing within single organizations and ISPs – 9 Routing-Update Algorithms – and routing between organizations – 10 Large-Scale IP Routing.

    But before that, in the next chapter, we compare IPv4 with IPv6, now twenty years old but still seeing limited adoption. The biggest issue fixed by IPv6 is IPv4’s lack of address space, but there are also several other less dramatic improvements.