Each new version of the Linux kernel brings new features. Version 5.3 includes a small change to the handling of IPv4 packets. IPv4 addresses are running out and some network engineers are trying to recover as much IPv4 addresses are possible.

The best approach to recover IPv4 addresses is to contact the owners of large address blocks and encourage them to return them to the address registries. Some organisations prefer to sell them. A recent example concerns the AMPRNet, Amateur Radio Digital Communications. In the early days of the Internet, some hams got interested in Internet protocols and Hak Magnuski convinced Jon Postel who lead the address registry to reserve a block of 16 million IP addresses, 44.0.0.0/8 for amateur radios. Some of them reserved subblocks and used it for experiments with packet radio networks. However, as the Internet got deployed, interest in amateur packet radio networks decreased and 44.0.0.0/8 is far from being fully used. Earlier this year, the managers of this address block agreed to sell four million addresses, 44.192.0.0/10, to Microsoft.

Another way to recover IPv4 addresses is to look at the reserved blocks in the IPv4 Address Space Registry. The first reserved block is 0.0.0.0/8. This block was reserved by RFC1122 to identify a host on the local network. This document also prevents the transmission of packets from a source address with 0 as the high order byte. However, this recommendation is not widely used. Linux version 5.3 will support the utilisation of IP addresses in the 0.0.0.0/8 block. If you plan to use such addresses, beware of possible compatibility problems with other devices that still support RFC1122. If you do not have enough IP address, you’d better continue to deploy IPv6 instead of seeking the remaining IPv4 addresses…

This blog post was written to inform the readers of Computer Networking: Principles, Protocols and Practice about the evolution of the field. You can subscribe to the Atom feed for this blog. These notes are also posted on the e-book Facebook page