Opening and Closing TCP ports

[General Zod]

At the moment I'm running a windows 98 box. (Unfortunately. Though it should only be for another week or so). What I'm wanting to do is figure out how to open and close my internet ports manually, but so far I haven't been able to find much in the way of info on how to do this.

While I realise I could probably do this with the built in modem firewalls, I'd prefer to figure out how to do this by hand if possible. If anyone can explain how this is done, or better still post a link to a site that can show me what I'd need to do (without installing third party software, preferably), it'd be appreciated.

[Alferd Packer]

From Microsoft:

Versions of Windows before Windows XP did not come with a built-in firewall. If you have a computer with an earlier version of Windows, such as Windows 2000, Windows Millennium Edition (Me), or Windows 98, you should get a firewall and install it. You can use a hardware firewall or a software firewall. The following resources provide more information about your firewall options...

Of course, you probably only have a handful of ports open anyway, since you're probably not running many services. If you're really concerned, you need a commercially available stateful firewall application, or a spare box with Linux installed. That comes with a stateful firewall called iptables.

EDIT: Of course, if you're just interested in opening and closing ports, then what you should do is portscan your Win98 box, figure out what services are holding ports open, and start disabling those services. nmap is an excellent port scanner for Linux; I don't know if there is a Win98 port of it available, or if there are open source portscanners for Windows.

[Pu-239]

nmap only works on WinNT derivatives (not 95/98/ME)

[Spacebeard]

While I realise I could probably do this with the built in modem firewalls, I'd prefer to figure out how to do this by hand if possible. If anyone can explain how this is done, or better still post a link to a site that can show me what I'd need to do (without installing third party software, preferably), it'd be appreciated.

As others have mentioned, you could run nmap from a Linux or WinNT machine. There are also some web-based port scanning services you could use... DSLreports has one here. Steve Gibson's online scanner at grc.com is also popular, and decent enough for examining Windows PCs, but take everything he says on his website with a truckload of salt; the man's an ego-driven charlatan and snake oil salesman.