Nmap Development mailing list archives
Re: weird nmap problems
From: Diman Todorov <diman () xover mud at>
Date: Wed, 12 Jul 2006 17:24:21 +0200
By default, nmap will try to discover if the host is active before scanning, which (by default) uses the ICMP echo request / reply method. If the host is not discovered, nmap will consider the host not up (and all ports on it filtered). When you specified -P0, you requested nmap to skip the host discovery phase and perform the TCP connect scan (default scan type) on the port specified. Clear as mud, eh? ;-) So, the results you had in all cases are expected and nmap is performing correctly.
it is not so simple :) By default nmap uses several methods to determine if the host is up: In nmap.h you can find the line: #define DEFAULT_PING_TYPES PINGTYPE_TCP|PINGTYPE_TCP_USE_ACK| PINGTYPE_ICMP_PING If you don't specify P0 then nmap tries to connect to port (surprise surprise) 80. If port 80 responds with a packet, then the host is determined to be up. Additionally nmap tries an icmp ping. The catch is that the massping function which handles host uppedness doesn't use the same code to attempt connecting to port 80 like the function which port scans port 80. If you don't specify P0, nmap tries to connect to port 80 to determine if the host is up. I am not sure what happens from this point. It is possible that the web server doesn't like being harassed twice in a short time interval. This time interval is probably longer than nsock is willing to wait for a SYN ACK. My reasoning however is mostly guesswork. Joshua, I suggest that you try to reproduce the issue with a more recent nmap version. You say that you're running 3.95 but 4.11 is the current stable version. You could also run nmap with -vv -d --packet-trace to make it tell more verbosely what exactly it is doing. I will be more likely to pinpoint your problem with more debug information :) cheers Diman _______________________________________________ Sent through the nmap-dev mailing list http://cgi.insecure.org/mailman/listinfo/nmap-dev
Current thread:
- weird nmap problems Joshua Perrymon (Jul 11)
- Re: weird nmap problems Jon Passki (Jul 12)
- Re: weird nmap problems Diman Todorov (Jul 12)
- Re: weird nmap problems Jon Passki (Jul 12)
- Re: weird nmap problems Diman Todorov (Jul 12)
- Re: weird nmap problems Jon Passki (Jul 12)