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Re: Nmap says Host down when actually host is up.
From: "DePriest, Jason R." <jrdepriest () gmail com>
Date: Mon, 22 Oct 2007 16:14:46 -0500

On 10/22/07, Swapnali  wrote:
Hi,

I am using nmap 4.20 for windows. I am working on a windows xp with sp2. I
have tried to find the solution for my problem on the nmap lists but it
didn't help. Hence this mail.

I have tried many host discovery options to figure out why nmap says a
particular host is down when actually the host is up. Enclosed is also the
screenshot of the nmap response as opposed to the icmp ping response to a
particular IP along with the ethereal snapshot. When I do icmp ping, I do
receive the reply. But when I use "nmap -sP <ip>" the response I receive is;

                   Starting Nmap 4.20 ( http://insecure.org ) at 2007-10-22
14:49 Central Daylight
                   Time
                   Note: Host seems down. If it is really up, but blocking
our ping probes, try -P0

                   Nmap finished: 1 IP address (0 hosts up) scanned in
4.188 seconds

I used ethereal to check whats going on. I saw a ping request going to a
destination IP and a reply from another interface of the same machine with a
different IP in the source with icmp seq. number being the same. Is nmap
matching both destination IP in request and src ip in reply packet? If this
is the case, it might be a bug. Because, as in this case a machine might
have multiple IP's. Infact I am facing this problem with many hosts.  Am I
missing something here?
I will appreciate any help/ info on this. Awaiting a positive response.

-Swapnali


Greetings, Swapnali,

Try running nmap against a single trouble system
nmap -sP <host>
but include -vv (that is two v's and not one w) and --packet-trace as well
so
nmap -sP -vv --packet-trace <host>
That should provide helpful information for you and for the list.

-Jason

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