a basic nmap usage question

[suiqiangd () gmail com]

hi,

I have a basic nmap usage question. not sure if this is the right place to  
ask. Please let me know if anyone know a better place for this.

I am using nmap as a TCP SYN packet generator to test out my firewall. It  
works well so far. However, one thing that I don't know how to control is  
that it generates 2 SYN for each destination port when SYN is not replied,  
ie when the first SYN is filtered, nmap sends another SYN to try again. The  
command I use is:

nmap -sS -PN -r -p500-504 32.1.1.6

How can I disable this retry and tell nmap to only send 1 SYN packet for  
each destination port? I looked through the man page but didn't find such  
knob.

Thanks,
Suiqiang
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