Comment 1 for bug 1655049

Can you provide the first 3 octets of one of the bad MACs? If you're not sure which one, the following is sure to catch it:

sudo maas-region dbshell
select distinct substring(cast(mac_address as varchar) for 8) from maasserver_interface;

This would appear to be a bug in the python3-netaddr, which MAAS should probably armor itself against.