> On Fri, 18 Aug 2017, Dan wrote:

>> Every day, just after midday, I suddenly lose access to DNS name
>> resolution, and therefore become unable to interact with any remote
>> hosts, even though my network interface is still up.

On Fri, 18 Aug 2017, Howard, Chris wrote:

> Do you think it might have something to do with your DHCP lease
> expiring?

Thanks, Chris, but it doesn't look like it.  On Friday (August 18th),
the failure of name resolution happened between 12:25 and 12:30.  In
/var/log/messages, I find the following entries apparently relevant to
when DHCP leases were due to expire:

Aug 18 12:00:47 shepherd rsyslogd: [origin software="rsyslogd"
swVersion="7.4.7" x-pid="1100" x-info="http://www.rsyslog.com"] start
...
Aug 18 12:00:53 shepherd dnsmasq-dhcp[2445]: DHCP, IP range
192.168.122.2 -- 192.168.122.254, lease time 1h
...
Aug 18 12:01:03 shepherd NetworkManager[1019]: <info>
[1503054063.6017] dhcp4 (wlp2s0):   lease time 86400
...
Aug 18 12:01:03 shepherd dhclient[2380]: bound to 10.188.20.97 --
renewal in 39007 seconds

I think the first symptom of the loss of name resolution is probably
represented by this entry:

Aug 18 12:29:54 shepherd firefox.desktop:
1503055794168#011addons.update-checker#011WARN#011Update manifest for
[log in to unmask] did not contain an updates property

You'll note that all this has been happening on a wireless interface
(wlp2s0) - my employer's wi-fi network.  Yesterday in the crucial
period between midday and 1pm, I was connected to my employer's wired
ethernet network instead, and the problem didn't arise.  I'll go
wireless again for the relevant period today, and if I lose name
resolution, I'll try Andrew's ping -n suggestion for further
diagnostic data.

-- 

Thanks,

Dan