mac48.nx

mac48.nx -- IEEE 48-bit Ethernet MAC address parse + format. 6-byte unique identifier, printed as six hex pairs separated by ':' (IETF canonical) or '-' (Microsoft) or '.' (Cisco three-group form -- rare, not produced by us). Use cases: NAS monitoring, firewall rule generation, DHCP static leases, Wake-on-LAN packet construction, switch port lookup, Nishi-controller device identity. OUI lookups (first 3 bytes = manufacturer) are a future mac48_oui.nx if Nishi-monitoring needs them -- that's a data table problem, not algorithm. Invariants: M1 Parse accepts both ':' and '-' separators, case-insensitive hex. Three-group Cisco notation (dotted) NOT accepted. M2 Format emits lowercase hex with ':' separators (IETF canonical). A mac48_format_upper / mac48_format_dash can be added later if needed. M3 Output length fixed at 17 bytes (6*2 hex + 5 separators).