Nmap Scanning Issue

[Frank K <fski82 () yahoo com>]

Good afternoon!  I really hope I'm emailing the right list, but I was referred to this list from the Nmap site.
 
We have been using Nmap in our organization through a proxy to see what ports are being seen as open from the outside.  
When I run Nmap looking for one specific port (i.e. 25) it finds all filtered except the mail hosts on our network, so 
it looks like it is working fine.  However, when I run the same command looking for all open ports on our subnet, all 
of a sudden it no longer finds the open Port 25's plus the other ports we know are definitely open...all I get are a 
few 80's and 443's....and I mean only a few.

I have used the following commands:

        * Single Port:  nmap -PN -p 25 -oA Test25_93013 xxx.xxx.xxx.xxx/16
        * Well Known Ports:  nmap -Pn -p 0-1023 -oA WellKnown_092613 xxx.xxx.xxx.xxx/16
 
I have tried experimenting with various other Nmap commands, but nothing seems to give me a good solid reading on what 
the actually open ports are.  What am I doing wrong?  I know I am missing something and it is probably pretty obvious.

Also, the scan I have been running is taking a long time (121 hours and only 2112 hosts complete).  I did some research 
and there is no way to gauge a time since it depends on numerous factors, but I was just wondering if this seems normal.

I really appreciate the help!  We really want to make sure we are compliant and to ensure the tool is working correctly.

Thank you so much!
Frank
_______________________________________________
Sent through the dev mailing list
http://nmap.org/mailman/listinfo/dev
Archived at http://seclists.org/nmap-dev/