Raw Sockets

Chapter 11

Raw Sockets

A raw socket is one that allows access to the underlying transport protocol. This chapter is dedicated to illustrating how raw sockets can be used to simulate IP utilities, such as Traceroute and Ping. Raw sockets can also be used to manipulate IP header information. This chapter is concerned with the IPv4 and IPv6 protocols only; we will not address raw sockets with any other protocol because most protocols (except ATM) do not support raw sockets. All raw sockets are created using the SOCK_RAW socket type and are currently supported only under Winsock 2. Therefore, neither Microsoft Windows CE nor Windows 95 (without the Winsock 2 update) can use raw sockets.

In addition, using raw sockets requires substantial knowledge of the underlying protocol structure, which is not the focus of this book. In this chapter, we will discuss ICMP, ICMPv6, and UDP. ICMP (both versions) is used by the Ping utility, which can detect whether a route to a host is valid and whether the host machine is responding. Developers often need a programmatic method of determining whether a machine is alive and reachable. We will also examine UDP in conjunction with the IP_HDRINCL socket option to send completely fabricated IP packets. For all of these protocols, we will cover only the aspects necessary to fully explain the code in this chapter and in the example programs. For more detailed information, consult W. Richard Stevens's book on IP, TCP/IP Illustrated, Volume 1 (Addison-Wesley, 1994) or the individual RFCs for each protocol.