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Re: Why does nmap send multiple probes to the same port?
From: Andreas Ericsson <ae () op5 se>
Date: Thu, 12 Jan 2006 01:56:04 +0100

chok () chokmah org wrote:
I am having trouble with nmap sending multiple probes to 
the same port to the same target. Because of this, a scan 
of all ports takes many days instead of an hour or two. I 
am using nmap version 3.81 on debian 3.1 (sarge).

Here is what the scan looks like:

# nmap -sT -P0 -p 1-65535 --packet_trace 192.0.2.1

Starting nmap 3.81 ( http://www.insecure.org/nmap/ ) at 
2006-01-06 09:47 CST
CONN (0.3610s) TCP localhost > 192.0.2.1:21 => Operation 
now in progress

It doesn't. EINPROGRESS (the macro for the error-code being returned) is 
returned, but that doesn't mean nmap is sending the packet. Here's what 
the connect(2) man-page has to say about it;

---8<---8<---8<---8<---
The  socket  is  non-blocking  and the connection cannot be
completed immediately.  It is possible to select(2) or poll(2)  for
completion  by  selecting  the  socket for writing. After select
indicates writability, use getsockopt(2) to  read  the  SO_ERROR
option  at  level  SOL_SOCKET  to determine whether connect
completed  successfully  (SO_ERROR  is  zero)   or   unsuccessfully
(SO_ERROR  is one of the usual error codes listed here, explaining the 
reason for the failure).
-----------------------

-- 
Andreas Ericsson                   andreas.ericsson () op5 se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231


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