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C.3 What are LISTENING ports?

  Suppose you did ``netstat -a'' on your machine and ports 1025 and 1030 showed up as LISTENing. What do they do?

Right, let's take a look in the assigned port numbers list.

    blackjack       1025/tcp   network blackjack
    iad1            1030/tcp   BBN IAD

Wait, what's happening? Has my workstation stolen my VISA number and decided to go play blackjack with some rogue server on the internet? And what's that software that BBN has installed?

This is NOT where you start panicking and send mail to the firewalls list. In fact, this question has been asked maybe a dozen times during the past six months, and every time it's been answered. Not that THAT keeps people from asking the same question again.

If you are asking this question, you are most likely using a windows box. The ports you are seeing are (most likely) two listening ports that the RPC subsystem opens when it starts up.

This is an example of where dynamicly assigned ports may be used by server processes. Applications using RPC will later on connect to port 135 (the netbios ``portmapper'') to query where to find some RPC service, and get an answer back saying that that particular service may be contacted on port 1025.

Now, how do we know this, since there's no ``list'' describing these ports? Simple: There's no substitute for experience. And using the mailing list search engines also helps a hell of a lot.

Vesaria, LLC



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