And you are spot-on there. It is unique to a device, which is why it includes at least six octets. When there is an ASP within an OS/System, ASP quotes it. In Mac OS X it is called both ethernet address (in System Preferences/Network/Ethernet) and MAC address (in System Profiler/Network).
Some manufacturers, including Asanté, used three common octets (eg, 00:00:94:nn:nn:nn in Asanté's case) for their production. The lateness in the manufacturing process of assignation of a MAC number is sometimes shown by manuscript addition of the device-specific octets on the MAC label.
Misfortune aside, it should be attached to the outside of the device. However, an IP address, which is mutable, is a far more convenient way of addressing a device. If you have a Mini EN/SC, you have a fixed SCSI ID=6 built into the device, in the same way as the Desktop EN/SC, so no other SCSI (such as the HDD) device may also use ID=6. The considerably larger Asanté EN/SC adapters with Thick/Thin/UTP have SCSI ID selector switches 0-7. I use both desktop kinds for my Classic and Classic II Macs (as expansion-challenged machines), with no difficulties of recognition between them and a (Netgear) 10Base-T hub, which is in turn downstream from a 10/100Base-T switch.
What activity do the LEDs of the EN/SC show? Apart from a steady PWR LED, the LI (Link) LED should stabilize also if there is a successful handshake.
Remember, you have multiplied your peril by mixing SCSI voodoo with ethernet voodoo. If you daisy-chain the external HDD and the EN/SC, you will have difficulty in having the adapter recognized if the HDD also retains its SCSI termination. The EN/SC has non-removable termination, and therefore must be the physically last device in the external daisy-chain. There is the further complication that early PBs lacked SCSI termination at the host-controller end, and sanity is often restored to the user only when a passthrough terminator is connected to the PB before any SCSI devices. The Mini EN/SC probably has this termination built into its connector specially. How then are you connecting the HDD to the EN/SC, which comes with the necessary HDI-30 connection inbuilt? Try your ethernet connection with only the EN/SC attached to the PB. That way you can establish that an ethernet connection is possible, and even then you may run into trouble with the inbuilt (both sides) termination of the Mini EN/SC if you attempt again to daisy-chain the HDD to the EN/SC.
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