Re: Ping scan misses my ASUS router, but nmap finds it

[Daniel Miller <bonsaiviking () gmail com>]

Dan,

Thanks for the report. We have been tracking an issue with ARP host
discovery on fast networks on Github for a long time [#92], but haven't
gotten any good leads on what might be causing this. I hope you can
participate over there. I would be particularly interested in answers to
the following questions:

1. Does Nmap (Zenmap) consistently miss this host, or does it sometimes
find it?
2. Does Nmap miss other hosts on the network, too? Any more or less often?
3. Does Nmap miss this host if you specify 192.168.43.2-254 instead of the
range you scanned?
4. Can you provide output of nmap -sn -d --packet-trace 192.168.43.0/24
5. Can you provide a packet capture (using tcpdump, wireshark, or similar)
of a scan where Nmap missed this host?

That last one would actually be the most helpful, since it would let us
know what Nmap is doing on the network.

In the meantime, if this is really causing problems, you can avoid specific
problems with ARP host discovery (at the cost of a little extra scan time)
by adding --disable-arp-ping to your scan options.

Dan

[#92] https://github.com/nmap/nmap/issues/92

On Sat, Apr 22, 2017 at 6:49 PM, Dan Dascalescu <ddascalescu () gmail com>
wrote:

> The same command fails to find my ASUS router in Zenmap, while nmap finds
> it:
>
> nmap -sn 192.168.43.0/24
>
> Moreover, I was running Zenmap in root mode, and nmap without root
> privileges.
>
> Tried this twice, and the 192.168.43.2 router wasn't found. This makes me
> not trust Zenmap for anything, if it can just miss hosts like that.
>
> Screenshot: http://imgur.com/a/ddkeR
>
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