Target settled: nh3-servers VLAN 50, static 10.100.50.60. Clear of the four
existing statics and below the .150 DHCP pool where fleet statics live.
The playbook never leaves itself one path back. Wi-Fi stays up throughout while
the wired interface is configured beside it; the new address is verified from
outside before anything is torn down, and Wi-Fi teardown is explicitly a
separate later change. A botched netplan therefore costs a retry over Wi-Fi
rather than a trip to the rack — which is what substitutes for 'netplan try',
whose interactive rollback needs a TTY that elway cannot provide.
Two preconditions are asserted as steps rather than assumed: the interface must
have carrier (writing a static config for a dead NIC and reporting success is
the failure this avoids), and its MAC must match, since interface names can
renumber across kernels but MACs do not.
Requires nothing from the operator beyond racking the box. The wired NIC has a
distinct MAC from the Wi-Fi one, so the post-move address and switch port are
both discoverable from the UDM rather than needing to be relayed.
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