So we moved a RHEL6.x server from one colocation to another. Unfortunately since RHEL 6, Redhat decided to include network manager by default. This makes for some fun times when trying to manually change IP information.

Another unfortunate was that the uninstaller of the system failed to document where each ethernet cable was connected. We needed 2x LAN LACP, 1x backup, 1x IPMI. The IPMI was easy, but this server had 4 onboard gig ports and 2 pcie riser gig ports to contend with. And both sets were BCM drivers – Broadcom.

Network manager was less than helpful in telling me which ports to plug into. NM was showing eth4 (configured), eth5, eth6, eth7 (configured), eth8, eth9. WTF.

I needed to find out which ethernet devices were active now that I plugged them in.

ip link show
Showed me all of the interfaces, physical addresses, and if it was up or down (connect)

From there I learned that eth9 was now LAN and eth7 was backup – so I could edit the network files to change those.

NM, however, had different plans. Since the eth4 was still configured with the old IP range, routing wasn’t happy when I tried to access said range over the MPLS.
ifdown eth4

Error: Device ‘eth4’ (/org/freedesktop/NetworkManager/Devices/4) disconnecting failed: This device is not active.

F YOU!

ip link set dev eth4 down
or
ifconfig eth4 down
Worked much better.