Enterprise Linux 7.3 makes some backwards-incompatible changes to interface names

Today, I was caught off guard by a change in Enterprise Linux 7.3. Apparently, systemd was assigning interface names like eno16780032 based on “garbage” data. I’m not really a fan of ANY of the names the modern schemes generate, what was the problem with eth#? But that’s beside the point. What hit me was that starting in 7.3 the garbage data is now being discarded and this results in a change in interface names. All this, in a point release. Here’s KB 2592561 that details the change. This applies to both Red Hat EL and CentOS, and presumably other members of the family based on RHEL 7.

The good news is that existing nodes that are updated are left alone. A file is generated to preserve the garbage data and your interface name. Unlike other udev rules, this one ONLY applies to existing systems that want to preserve the naming convention:

[root@kickstarted ~]# cat /etc/udev/rules.d/90-eno-fix.rules
# This file was automatically generated on systemd update
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:50:56:95:de:4e", NAME="eno16780032"

As you can see, it’s based on the MAC. That’s the bad news. If you plan to use the node as a template to deploy other VMs, the resulting VMs will effectively receive “new” interfaces based on the new MAC, resulting in ens192 instead of eno16780032. This definitely introduces at least one minor issue: the eno16780032 configuration is left intact and the interface is missing, so every call to systemctl restart network generates an error. It can also cause other issues for you if you have scripts, tools, provisioning systems, etc., that are predicting your nodes will have interface names like ens192. This is not difficult to remedy, thankfully.

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