Understanding Linux Network Internals

Chapter 29. Neighboring Subsystem: Miscellaneous Topics

With this chapter, we conclude the part of this book on the neighboring protocol. The chapter shows how the user-space commands used to configure neighboring protocols interact with the kernel, summarizes the variables and functions introduced in the previous three chapters in easy-to-read tables, and concludes with a detailed description of the main data structures used by the neighboring subsystem.

System Administration of Neighbors

Neighbor entries can be added, removed, and modified with two user-space tools:

arp

This is the older tool. It is part of the net-tools package, which includes other common commands such as ifconfig, route, netstat, etc. arp handles entries only for the IPv4 neighboring protocol ARP, as the name indicates. Like its companions, arp uses ioctl calls to communicate with the kernel.

ip

This is considered the current tool. The ip command is part of the IPROUTE2 package and is used to configure a wide range of networking subsystems (routing, traffic control, etc.). It can be used to configure any neighboring protocol, and it talks to the kernel using the Netlink socket.

Both tools can also be used to configure destination-based proxying.

This chapter does not go into detail on the commands’ syntax, features, or implementation, but it is worth knowing what is executed on the kernel side when the commands manipulate a neighbour entry.

The next three sections give you an overview of how configuration commands ...