Hello, I have a networking question. I connect to the internet using a Cisco 675 DSL modem, and I've noticed that it acts as a firewall, meaning I have to enter NAT information into the modem for it to do port mapping, to allow communication through certain ports. I need to do this for several programs I have, and set which port I opened for them, but my question is: how do I know what port numbers are available, which ones I can open for these programs? Any help or leads would be appreciated!

If the app relies on incoming info on a certain port, then your documentation should state what you are looking for. However, if you just want to know what the majority of your system is using for ports, then go to the

c:\winnt\system32\drivers\etc\services

file. This will show what port is mapped to what function (see example below).

ftp-data 20/tcp #FTP, data
ftp 21/tcp #FTP. control
telnet 23/tcp
smtp 25/tcp mail #Simple Mail Transfer Protocol
time 37/tcp timserver
time 37/udp timserver
rlp 39/udp resource #Resource Location Protocol
nameserver 42/tcp name #Host Name Server
nameserver 42/udp name #Host Name Server

This is a sample of what is setup by default with Win2K on my system. Now here is what I had to do to connect to our ERP system;

011gui 5627/tcp # inserted by MFG/UTIL 11/17/98
011cfg 5637/tcp # inserted by MFG/UTIL 11/17/98
011play 5647/tcp # inserted by MFG/UTIL 11/17/98
011prod 5657/tcp # inserted by MFG/UTIL 11/17/98
011mfgtrain 5667/tcp # inserted by MFG/UTIL 11/17/98

The names "011xxx" match with databases in our test environment. When we connect to a database, we just use the "service" name (name mapped to a given port in this file). Once you know what port you have this traffic on, you should be able to go into your router and define the port number to forward all traffic to your PC's IP. Bear in mind that some apps won't list (and don't need to) what port they use in this file (important ones like Q3A and UT come to mind :)). This should give you a good idea of what traffic your machine requires. In addition, some apps will work fine without port-forwarding from your router (like web browsing and FTP client usage).

HTH

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Regards,

clutch