nmap slow on second set of 64 hosts?

[Trevor Stevado <trevor.stevado () gmail com>]

I've been doing some nmap scans with the following switches:

-A -Pn -oX xmlfilename.xml -oG grepfilename.out

on a /24 network.  It zips through addresses x.x.x.0-64, but then when
trying to do the stealth syn scan of addresses x.x.x.65-128 it slows to a
crawl and says it's going to take hours to finish.

I've had the same experience on two seperate networks, running from a kali
linux vm on a macbook pro, or from the macbook pro directly.  A co-worker
has also experienced the same issue on the network.

Is there something messed up with nmap that is causing it to choke on the
upper range of hosts, or could it be something on the network?  The last
network I scanned like this the IT admin said there was nothing that would
be throttling the connections.

Any tips or advice on how to diagnose?
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