-----Original Message-----
From: Chris Harvey <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Wednesday, October 11, 2000 1:50 PM
Subject: Re: Port descriptions?
>Perfect,
>Second followup question.
>
>I'm watching requests go from my machine to my ISP's DNS server and calling
>on ports ranging anywhere from 1039 to 1108 (recently). If I close down
>those ports I can't seem to get a response from an 'nslookup' and email
>stops arriving too.
>
>Why would my RH 6.2 machine call out on ports other than 53 or 42 which
seem
>to be the ports for nameservers?
>
>The longer I watch it the higher the calling number goes and it seems to
>call sometimes on UDP and other times on TCP.
>
AFAIK your DNS requests are recieved on your ISP's port 53, and replies are
gotten back by your system on ports greater than 1024. Those ports above
1024 being unpriviliged ports. Same thing generally works for the rest of
the services. ftp is port 21, telnet is port 23, smtp is port 25, dns is
port 53, http is port 80, etc... You can see the whole list in
/etc/services. The alternating of dns from upd to tcp is based on the
packet size, if I recall correctly. It's usually udp, but switches to tcp
if too large. There's a lot to learn there, a few books and perhaps
checking out the info in the ipchains docs could give you a bit more
information. Hope this helps.
Jeff Hogg
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