[CentOS] Strange network failure on C6

[Rob Kampen]

On 05/15/2015 08:09 AM, Fred Smith wrote:
> Hi all!
>
> I'm running C6 (up to date) on x86-64. have been running on the same
> system for over a year.
I've been running mine for three + years and have had this randomly 
occur only over the last year or so
> a couple of times lately access to the outside network has suddenly
> stopped working for reasons that I didn't figure out until it happened
> again yesterday.
>
> I had the time to fool with it, yesterday, so after quite a bit of
> head-banging I found that it had no default route set up (to make this
> story less long...).
>
> An appropriate route command "fixed" it and all was well, but...
> I had rebooted several times, among other drastic actions, such as
> rebooting the router and cable modem, and none of those things helped.
> so whatever it was that lost the default route was persistent across
> boots, while the manual route command to re-add it was NOT persistent
> across boots.
>
> At some point in fooling with it, I did something--and right now I have
> no idea what it was--that suddenly caused routes to persist across boots.
> I know I did not change any of /etc/sysconfig/network*, but I did look
> at them and saw that ifcfg-eth0 DID contain a line for default route,
> even though the route command did not reflect it.
Not sure what I did to fix it but check these:
Do you have a GATEWAY=192.168.1.1 in the /etc/sysconfig/network file?
plus in the ifcfg-eth0 file
make sure DEFROUTE=yes
I actually have a GATEWAY line in this file too plus DNS1= and DNS2=
and in case it wasn't obvious NM_CONTROLLED="no"

After all this my network comes up about 29 times out of 30, randomly it 
doesn't and then I just "sudo service network restart" and all is well.
Just fyi, I also find randomly that the gnome login list sometimes sorts 
alphabetically rather than the default of by UID, no major difficulty 
but I am sure this kind of randomness is a fairly recent occurrence.
>
> So, if anyone has any good guesses on what the heck happened here, I'd
> like to hear them.
>
> thanks in advance!
>