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FAQ
This section is going to be constantly updated. Ask me more questions, and I'll add them here.
Q: Scanner locks up my connections. Is it normal?
A: If you have a Win95 or Win98 it's, er, "normal". You can avoid this
by setting dynamic socket allocation. The thing is that Windows can't
works at the load the scanner can. The number of socket descriptors is
limited, and it results in the lockdown effect - when system can't open
a new connection in another applications. Set the "dynamic socket
allocation" switch in the option on. It will help. NT has no socket
limits, but still be careful with a system resources.
Q: My connections seem to slow down or stop to respond, when I run NScan.
A: Sure, they will. You can't place a megabit load on the network while
sitting on dial-up connection. You have to limit the speed, or you can
also get an inadequate results - some open ports may be skipped. There
is a limit you can set in an Options dialog.
Q: I tried to scan some ports on the server xxx.xxx.xxx.xxx. Port 80
was open, I could connect on it using Telnet or Iexplore. The scanner
only reported port 25. I tried to scan only port 80, but it didn't
detect it. What could be the cause?
A: That's really nice problem. The key of the problem is that that host
can have a slow connection. If you'd used detailed output (absolute),
you could notice that there are not only "connection refused" messages,
but also "timeout" lines, that have only 2
meanings - one of the hosts is too slow (his or yours) or it's
firewalled. Set detail level at least to "timeouts" and look (this is
sometimes a really a powerful feature), maybe you'll find the balance.
Just note that open ports will come up even if you have more than a
half timeouts (don't lower the speed too much).
Q: I want to scan from 0.0.0.1 to 255.255.255.255 at the ports
1426,1436,1501,1644 because I'm looking for a Satellite communications.
When I insert these IP's, the program not scan. Why? How I can do it?
A: I did not found such a bug in those versions that I've not already
killed. But I really admire the problem... don't scan
such huge ranges, you will never scan all the Internet. It's accepted
by scanner and it could work.... but for too long. Try to think
yourself - your range applies to 17179869176 ports and even if you have
a speedy connection, the resulting traffic and therefore time will be
incredible (about 6-8 terabytes). Also please note that there is
reserved, broadcast and multicast addresses, as well as loopback
network (127.x.x.x). They will never be scanned correctly (only
localhost, but I can't imagine, why would you need to scan localhost
class A net).
Q: Scanner dramatically slows down when I scan the network. What is the problem?
A: You may have tried to scan reserved address block, invalid address
class or you may get a firewalled network. In both cases scanner can't
get the reply and waits until times out. Since Windows Sockets timeout
constants are relatively high, as well as it automatically repeats the
query several times, it's may take a long time to determine timeout.
You can see it in the report while using "timeout" detail level. The
examples are: D and more class networks (224.x.x.x and more) - invalid;
0.0.0.1 - reserved block; UUNET networks (port 31337 is firewalled by
UUNET's routers).
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