"Finding a server's BMC / IPMI IP address with ipmitool" – Jeff Geerling
This was useful, but I found it only showed IPv4 details.
My OOB network is IPv6 only (because I am a masochist).
After some searching I found that
ipmitool lan6 print
does the same but for IPv6. This appears undocumented in Debian despite it being the case since September 2016. I submitted a bug report.