Category Archives: Tips & Tricks

Using a telnet client as a port scanner

If you ever need to check if a TCP port is open or reachable, one easy way to do it is using a telnet client.

A telnet client actually comes with Windows, but for some annoying reason it is not installed by default. To install the windows telnet client you need to add it using the “Turn Windows features on and off” like so:

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Because Telnet is essentially just characters sent over a TCP connection, you can use the telnet client as a poor man’s TCP port scanner. To manually check if TCP port 80 is open or reachable on a server you can type telnet myserver.com 80.

As an example lets see if Google.com has port 80 (HTTP) open … 😉

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If you get a blank screen with a blinking cursor you have successfully connected to that TCP port.

In this example, if you are feeling particularly sadistic you can now engage in a HTTP conversation. Type GET index.html HTTP/1.0 and press enter and you will see Google’s home page being sent to you. Same idea would apply if you connected to most other TCP-based protocols; POP mail server etc.

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On the other hand if the TCP port is not open or not reachable you will see this:

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Troubleshooting ports and firewalls can be a pain. This is the simplest and quickest way I know for checking connectivity.

How to make a bootable Vista DVD using MKISOFS/CDRTOOLS

UPDATE: This is a repost of an old article that is still referenced on some forums.

I managed to get hold of an MSDN copy of Vista on DVD. Unfortunately the DVD was corrupt and several of the sectors were unreadable. I managed to salvage all the files from the disc apart from a couple named license.rtf (no big loss there then!). The question was, how do I then make another bootable DVD from these salvaged files? No big deal you say – just create a bootable ISO like you did with Windows XP: extract boot image then use that to burn the files to a bootable DVD with Nero.

Unfortunately this wouldn’t work because one of the files on the Vista DVD is > 2GB (install.wim) and the most common ISO modes (1 and 2) don’t support files that big. Microsoft have a solution of course: There is a utility on the Windows Automated Installation Kit (WAIK) called Oscdimg which is designed to make ISO images from Vista trees. Perfect, the download is here. Unfortunately its 900MB and I’ll be damned if im gonna download all that just for a 50k utility! So I decided to try using makeisofs (from the cdrtools package. N.B. for windows you will need to download a windows binary). After 20 minutes of fiddling around I got the following to work:

mkisofs -udf -v -b boot.bin -no-emul-boot -hide boot.bin -hide boot.catalog -o MyVistaIso.iso Vista

Where boot.bin is the name of the boot sector extracted from the orignal corrupt DVD, and Vista is the name of the directory containing the salvaged contents of the original DVD. Note: The boot.bin file must be within the Vista directory for mkisofs to find it. Anyway, I burned the iso to a DVD, restarted my PC, and it booted into the Vista installer. I proceeded to install Vista and everything worked fine. Yay!