Nmap Development mailing list archives
Re: Why does nmap send multiple probes to the same port?
From: Casey Williams <Lists () aviditysoftware com>
Date: Wed, 11 Jan 2006 23:11:23 -0600
On 04:37 Thu 01/12/06 Jan , Andreas Ericsson wrote:
Casey Williams wrote:I've noticed the same thing with -sS and -P0 which I did't think used connect(). I've actually been wondering about this recently myself because I've been writing my own lightweight port scanning engine using libnet to inject SYN probes. I've noticed that if I loop over the range of IP addresses and immediately send the probe, I won't always get a reply from hosts that I know should have replied. However, if I sleep() for 1 millisecond between probe sends, it *will* send the reply. However, this 1 ms sleep() can add up over many hosts/ports, and I can't seem to sleep() for a shorter period of time, (even nanosleep() doesn't seem to work for me). ***pure conjecture ahead*** So I started wondering how nmap was able to be so reliable and yet SO fast (kudos!). Then I realized that it may be sending these "retry" probes to hosts that it doesn't know the status of and that it didn't get a reply from. I've been reading the nmap source and stepping through it, but I haven't verified that this is correct. Am I on the right track? If not, would this tactic be unrecommended?You're missing the point a bit. The error messages means that nmap didn't send those probes. It tried to, but the system told it there was already a connection attempt in progress.
I'm slightly off topic since I'm talking about SYN scans instead of connect() scans, and I'm not certain how your reply would apply to these. (If it does apply to SYN scans, I apologize, I'm fairly new to this level of TCP/IP programming and I suppose I need to read more :)) In my case, when I try "nmap -sS -P0..." and I sniff the traffic that gets generated from that scan, I've noticed more than one probe gets sent to the same port on some of the hosts under certain circumstances. I shouldn't see these "extra" probes in the packet capture if NMap didn't actually send them should I? Is this the expected behavior, or am I imagining things? :) -Casey Williams _______________________________________________ Sent through the nmap-dev mailing list http://cgi.insecure.org/mailman/listinfo/nmap-dev
Current thread:
- Why does nmap send multiple probes to the same port? chok (Jan 11)
- Re: Why does nmap send multiple probes to the same port? Andreas Ericsson (Jan 11)
- Re: Why does nmap send multiple probes to the same port? Casey Williams (Jan 11)
- Re: Why does nmap send multiple probes to the same port? Andreas Ericsson (Jan 11)
- Re: Why does nmap send multiple probes to the same port? Casey Williams (Jan 11)
- Re: Why does nmap send multiple probes to the same port? Richard van den Berg (Jan 12)
- Re: Why does nmap send multiple probes to the same port? Andreas Ericsson (Jan 12)
- Re: Why does nmap send multiple probes to the same port? Casey Williams (Jan 11)
- Re: Why does nmap send multiple probes to the same port? Andreas Ericsson (Jan 11)
- <Possible follow-ups>
- RE: Why does nmap send multiple probes to the same port? chok (Jan 12)