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Those of you who know me will be aware that I eek out a meagre living as a Data Communications Engineer. In other words, I play with computers all day. The fact that after many long hours of study (there were at least three that I recall, although former classmates may dispute this claim), my life's work essentially involves building technology to facilitate access pornography with greater ease and speed than ever before only slightly dampens my enthusiasm for my chosen field of endeavour.
Over time, I've gathered lots of useful information on the subject which I've never really put to any good use. Some of it I wrote myself (mostly because I clearly need the writing-practice) and the rest is written by others wiser than I. You should only really rely on the technical veracity of the material in the latter category and should regard the home-grown stuff largely as fiction.
Seriously, though, I hope you find some of the useful, and your comments and suggestions are welcome. In particular, please do let me know if you think that any content is factually incorrect...
InternetA bunch of useful DNS diagnostic tools
Run a bunch of automatic tests against your mail relay to see if it is acting as an open relay
Find out what IP address you are browsing from (it is 98.84.18.52, incase you can't bear the suspense) and also see a bunch of other information your browser sends to my server
IPv4 IP Multicast IPv6An analysis of exactly how large the IPv6 address space really is and how it is allocated
A few handy tools for IPv6 IP address conversions and DNS lookups
Ethernet
VLAN Hopping
An analysis of how packets can be made to hop between VLANs on a switched Ethernet network and how to configure the network to make sure this doesn't happen
Serial Comms Cisco Tools & InformationA handy tool for use with IOS-based Cisco Catalyst switches (where you can't apply a list of commands to a bunch of interfaces in one go :-( )
A tool for generating a basic (very basic) access control list for your internet-facing router
This only works for "type 7" passwords. "Type 5" password can't be decrypted. The decryption is done in your browser. The password isn't transmitted anywhere.
Handy information about PIX specifications and configuration
Debugging Cisco PIX High CPU Utilisation
A short explanation of how to determine which process on your PIX is gone nuts and a Perl script to make it easier to do
Telnet/SSHAn excellent Telnet/SSH/Serial client. Also runs Cygwin in a nicer terminal environment. Fast, very nice GUI and does everything I want it to do (so far, anyway). The (separate) port-forwarding utility is a little iffy still, though.
A fine Telnet/SSH client which is absolutely free ! It also contains command-line implementations of SCP and SFTP (for secure file transfer over SSH)
Add tabs to PuTTY. This makes PuTTY just about perfect !
A little dated (it hasn't been updated since August 1999 !), Tera Term is still an excellent Telnet and Serial terminal emulator. With the addition of TTSSH, you can also do SSH version 1 with Tera Term. However, if you need SSH at all you are really better off with PuTTY (above)
UPDATE: There is an SSHv2/IPv6-capable version of Teraterm+TTSSH available at http://sleep.mat-yan.jp/~yutaka/windows/index.html. There is another version at http://www.ayera.com/teraterm/ which I haven't tried
A commercial (but very inexpensive) terminal emulator. It is a little more polished than PuTTY, but its chief advantage is that it works over the serial port also (handy for working on routers. 'headless' UNIX servers and the like).
An excellent graphical interface to SCP/SFTP to make secure file transfer very painless and easy
Network EmulationA network emulator for Linux capable of introducing latency, packet-loss, jitter and lots of other real-world network characteristics. A nice X-Windows GUI makes setting up your emulated network parameters nice and easy. A little tricky to set up but well worth the effort.
Another network emulator for Linux (built into the 2.4.27+ and 2.6.9+ kernels). See the "tc(8)" manpage for details
A similar tool to NIST Net, but based on the FreeBSD kernel. The best bit is that the whole thing is available as a bootable floppy disk. Just boot up, configure (sorry...no GUI !) and you are off.
Security(not even faintly technical, but too funny not to put here !)
Crypto & PKIQuick-reference sheet of useful OpenSSL recipies for converting X.509 digital certificates between different formats
A Java applet for decoding X.509 digital certificates and displaying their contents
Radius LDAP SNMPSimple realtime SNMP grapher. Produces a graph just like MRTG but does it in real time. Very simple, no nonesense, excellent utility that does just one thing very very well.
Full SNMP MIB browser. GUI is a little clunky and dated, but it does the job. Don't forget to download the MIB collection also.
Very nice MIB browser. Written in Java so runs on Windows or Linux.
Miscellaneous