IP stops returning to arp-scan when sshed into.

[Scott Cohen]

I posted this on the Ubuntu-MATE bug report before this (https://bugs.launchpad.net/ubuntu-mate/+bug/1711460), but I don't know how active that place is so I'm also going to post it here. I also don't know if this is the right package to post this in, but since there is no clear way to post bugs with ambiguous sources of problems, I am posting here.

When I do a scan of my local network via the command arp-scan --localnet, I find that the IP of the machine which has Ubuntu-MATE on it shows up in the list of IPs brought back by arp-scan. But when I ssh to that machine and then issue the command arp-scan --localnet from the machine that I had sshed from, I find that the IP address of the computer with Ubuntu-MATE on it is absent from the list. I expect the IP address with the machine with Ubuntu-MATE to show up. I tested this with other machines and operating systems and those still returned an IP address when issued arp-scan --localnet. The Ubuntu-MATE machine was the only one which didn't.

Description: Ubuntu Artful Aardvark (development branch)
Release: 17.10

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: network-manager 1.8.2-1ubuntu2
ProcVersionSignature: Ubuntu 4.11.0-13.19-generic 4.11.12
Uname: Linux 4.11.0-13-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.6-0ubuntu5
Architecture: amd64
Date: Thu Aug 17 14:19:46 2017
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2017-01-07 (222 days ago)
InstallationMedia: Ubuntu-MATE 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
IpRoute:
 default via 192.168.1.1 dev wlp7s0 proto static metric 600
 169.254.0.0/16 dev wlp7s0 scope link metric 1000
 192.168.1.0/24 dev wlp7s0 proto kernel scope link src 192.168.1.96 metric 600
NetworkManager.conf:
 [main]
 plugins=ifupdown,keyfile

 [ifupdown]
 managed=false
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: network-manager
UpgradeStatus: Upgraded to artful on 2017-08-11 (6 days ago)
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH CONNECTION CON-UUID CON-PATH
 wlp7s0 wifi connected /org/freedesktop/NetworkManager/Devices/3 Windows7Family 2 ea6b04bf-6ea5-4250-9783-f8df31fb090a /org/freedesktop/NetworkManager/ActiveConnection/3
 enp6s0 ethernet unavailable /org/freedesktop/NetworkManager/Devices/2 -- -- --
 lo loopback unmanaged /org/freedesktop/NetworkManager/Devices/1 -- -- --
nmcli-nm:
 RUNNING VERSION STATE STARTUP CONNECTIVITY NETWORKING WIFI-HW WIFI WWAN-HW WWAN
 running 1.8.2 connected started full enabled enabled enabled enabled enabled