Joe Hertvik, a system administrator for a midrange System i shop, recently wrote about the issues around migrating Ethernet line descriptions on the System i.
As you all probably know, Ethernet line descriptions allow i5/OS partitions to speak to one another over a sort of virtual network. Hertvik listed three reasons why someone would want to move line descriptions from one System i to another: to restore i5/OS to a new system during a hardware upgrade; to do failover processing for testing or real-world scenarios; or to restore your System i configuration on a DR machine.
But Hertvik explained that doing this Ethernet line description migration can cause them to not work properly:
In all three cases, the end result is that after the migration, you will have two machines containing the exact same Ethernet line descriptions, complete with all the same configuration parameters. Depending on how your lines are configured and what state each machine is in, this situation could prevent the Ethernet cards on both machines from broadcasting correctly in the same network.
Hertvik described two situations in his own shop, one when he was moving processing from a production box to a Capacity Backup (CBU) machine, and another when they were migrating an i5/OS partition from an old box to a new system. In both cases, Hertvik wrote that the target system’s Ethernet lines “froze up like Minnesota in January.”
As it turns out, the reason for it is that the Ethernet cards in the old systems do not necessarily shut down or stop broadcasting just because you put them in a restricted state. Hertvik goes into a lot more detail about the problem and its resolution, including line commands that he used, so it is worth reading the whole thing.