Hi, for permanent machines you should use wired networking. The bottom line
physics is this - the wires show the direction for the e-m waves to follow
the path between your computer and the network hub. Without wires (wi-fi),
the e-m waves are not sure which way to go and sometimes become lost.

So impossible to ensure reliable communication without wires.

If this happens during dhcp renegotiation, all bets are off as you are
hitting strange bugs in the dhcp renewal code - in the best case, it should
continue using the old dhcp lease, but maybe instead it keeps using the old
IP address but loses all DNS settings.

Who knows.

As a taste of possible bugs, RHEL/SL for years had a bug where ypbind would
quit (sometimes, eventually, hard to reproduce) if network is disconnected
for some time (traced does to a bad SIGPIPE handler, I think. Finally fixed in el7).


K.O.


On Wed, Aug 23, 2017 at 11:32:57AM +0100, Dan wrote:
> >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

-- 
Konstantin Olchanski
Data Acquisition Systems: The Bytes Must Flow!
Email: olchansk-at-triumf-dot-ca
Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3, Canada