Where is network configuration "hidden" on Ubuntu 16.04?

Dan Streetman dan.streetman at canonical.com
Mon Oct 8 22:51:21 UTC 2018

On Fri, Oct 5, 2018 at 3:31 PM Leroy Tennison <leroy at datavoiceint.com> wrote:
> I have two identical hardware devices, call them "2" (running Ubuntu 16.04.5 x86_64) and "5" (running Ubuntu 16.04.3 i686).  On "2" a couple of NICs failed so I replaced the chassis by doing a hard drive swap between "2" and "5".  I updated /etc/udev/rules.d/70-persistent-net.rules on the swapped hard drive and everything worked on "2" with the swapped chassis (this was the subject of my last post to this list).
> The chassis of "2" (the original "2") has enough good NICs to use for testing a planned keepalived enhancement but has the unit "5" hard drive.  I updated /etc/network/* (recursive) to have the configuration from "2" but, upon boot, the device keeps getting it's old IP address for eth3 and eth9 (the unit "5" IP addresses).  It gets the correct IP address for eth0, no IP address for eth5, eth6 or eth8 (all of which are configured as static in the interfaces.d file).  eth9 is the more unusual IP address so I did a recursive grep of /etc for it's first two octets and found nothing.  In fact /etc/rc.local has the default contents and neither /etc/network/interfaces or the file in /etc/network/interfaces.d even configures eth9.

It's unclear what configuration exactly you're using for each
interface, but if you're using dhcp then the dhcp server is likely
giving the same IP address to the nic mac address, so it would follow
the hardware (not your configuration).

If you're not using dhcp, then I suggest you post exactly your config
and what you want your nics to be configured as, and people can help
you adjust your files.

> Where else can I look for the remnnts of the "5" configuration which are being applied at boot and preventing parts of the file-based configuration from working?  I even decompressed a copy of initrd.img... and found nothing.
> Leroy Tennison
> Network Information/Cyber Security Specialist
> E: leroy at datavoiceint.com
> 2220 Bush Dr
> McKinney, Texas
> 75070
> www.datavoiceint.com
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