Folks,
I'm trying to close down some of the ports on my machine that are in the
1024 to 65535 range, and ideally I'd like to close them all down unless
there is an application that I know is listening on that given port.
What I see happening though is kind of interesting. If I make a DNS call or
SMTP, or basically anything including HTTP. The initial call goes out of the
registered port, 53, 25 and 80 respectively. However the response may come
back in on a completely different port, usually in the range of 1037 to
about 28xx. Is this standard TCP/IP behaviour?
I'm assuming my machine is making a call into another machine on the
registered port for the service, but also passing an alternative port number
that a response should be sent back on.
Therefore do I have to leave a range of ports open so that these
conversations can happen between applications without opening up the whole
range? Is the range defined anywhere, can I define it? Anyone know of any
sources I can read up on this?
BTW: I don't have portmapper running on the machine as I heard that was for
NFS. Is that right?
Chris
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