Network Troubleshooting Tools

Author: Joseph NB. Sloan



Publisher: O'Reilly

Reviewed by: Roger Burton-West

Network Troubleshooting Tools (the Basilisk book) is a book that has no clear brief. In theory it is an introduction to data-gathering tools for use when networking problems occur; in practice, it also deals with general network device management, monitoring, and diagnostic procedures. It tends to the superficial at times, in an attempt to include at least a mention of all this material, but manages to serve as a useful general introduction to network troubleshooting.

The book is openly biased towards Unix-based tools; however, there is a section at the end of each chapter introducing, and briefly explaining, Windows-based tools for those required to use them. Although it is clear that the examples are written with FreeBSD in mind, they are sufficiently generic that there is no difficulty in using them with Linux or Solaris.

The chapters are arranged in a step-by-step fashion, starting with connectivity: checking the local host configuration, basic point-to-point testing, and path testing. Next is packet capture and device discovery, ranging from passive listening to active port-scanning. At this point the book abandons its troubleshooting theme to include a fairly thorough treatment of SNMP; while this might be useful to some readers, it has the feel of filler material, having little to do with the book's primary purpose, except insofar as it lays groundwork for the next chapter's discussion of gathering of RMON data (as well as use of mrtg and ntop) for performance monitoring and location of network bottlenecks.

After this, the book returns to its main theme, with connectivity protocol testers (custom packet injectors, netcat, and load generators). There follows an overview of application-level tools, which consists largely of an explanation of how to telnet to ports 25, 80 and 110, followed by some notes on DNS testing, route checking and NFS.

The next chapter is a miscellany: capturing command sessions, remote logging by means of syslog, tcpwrappers, NTP and Tripwire. Finally, as a counterpart to the first chapter's generic troubleshooting instructions, is a section of specific instructions for troubleshooting firewalls, measuring performance, finding bottlenecks, and other such tasks.

The book is aimed at a fairly new network administrator; it serves as a light-weight introductin to networking (though it is pleasing to note that the traditional "this is how a netmask works" explanation has not been repeated here) and system administration, particularly in the early chapters. It is an excellent match to the skills required for network operations jobs, and is highly recommended for anyone starting in that role.

More experienced administrators may still find something of use in this book; while it does not by any means cover advanced concepts, its overview of programs may well include utilities new to the reader. There are some surprising omissions - mtr, for example, is significantly more powerful and easy to use than the path-timing utilities described here - but these are comparatively few.

The over-emphasis on SNMP is disappointing. While SNMP may well be suitable for use across an internal network, the inherent insecurity and difficulty of tunnelling a UDP-based protocol is not sufficiently emphasised. No attention is paid to alternative means of collecting current-function data - to network monitoring and alerting packages in general - although this could certainly have been considered within the book's ambit and would have added considerably to its value.

An omission of rather more concern is detail of the types of information one can usefully gain from interrogating dedicated routers; while the SNMP section describes one way of doing this, there is no discussion of how else one might obtain a routeing table from (e.g.) a Cisco or NetGear router, what other data are available, or what diagnostic procedures might be of use.

There is more general Unix administration information here than would be expected from a book focussed on network troubleshooting: use of ps and netstat, for example, should surely be familiar to an administrator before he is given responsibility for anything outside his own machine.

Overall, this is a useful book for the beginner and early intermediate network administrator, with strong emphasis on Unix both as a diagnostic platform and as the major component of the network.