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- Posted on
May 15, 2006, 3:44 am
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some (shared) servers it doesn't seem to be working. This makes me
currious - is it possible that these servers connections on specific
ports has been disallowed? If so, how would one go about doing this?
Also, how might I go about detecting it?
Re: unable to open socket connections on select ports?
Port 53 on the DESTINATION system, port 53 on the LOCAL system, or
both? Are you sure the destination system is running a server on
If the local system is running its own DNS server (may be a good
idea for a hosting web server) on port 53, you can't bind to port
53 on the local system because the nameserver is already using it.
Also, binding to low-numbered ports ( < 1024 ) may require root
privilege. But to talk to port 53 you don't need port 53 on your
Firewalls, either on the host itself (Linux and FreeBSD have things
like ipf and ipfw in the kernel if it's built that way), or it could
be a nearby Cisco router). Port 53 isn't something normally blocked,
though. It's sometimes the *ONLY* UDP let through.
I think you just did. Try to send a packet and see what comes back
(ICMP port unreachable, ICMP host unreachable, ICMP prohibited, nothing,
or a response) with something like tcpdump.
Gordon L. Burditt