ePMP mac address derived from LAN - Confirm understanding & long term stability

Hi Cambium team, I’m working on network automation stuff based on Cambium Devices.

I’ve observed that the mac addresses for subscriber modules are derived from the LAN mac address as follows:

Type Network mode Value Description
LAN Mac Address Both BC:E6:7C:AA:BB:C0 Always the same
WLAN Mac Address Bridge BC:E6:7C:AA:BB:C1 It adds 1 to LAN Mac
WLAN Mac Address NAT 02:E6:7C:AA:BB:C1 It adds 1 to LAN Mac, and replaces the first two letters with 02
WAN Mac Address NAT BC:E6:7C:AA:BB:C1 Same as WLAN bridge

I would like to confirm the following:

  1. That the understanding based on the table above is correct
  2. That you’re always replacing the first two digits with 02 on NAT network mode
  3. If this can be considered a stable/long-term API that won’t break changes in the future

Thanks!

Hi,

Currently the following logic is implemented:

Type Network mode Value Description
LAN MAC address Both BC:E6:7C:AA:BB:C0 Eth MAC = ESN
WLAN MAC Both BC:E6:7C:AA:BB:C1 ESN +1
Separate MGMT Interface MAC NAT 02:E6:7C:AA:BB:C1 Currently the first octet is converted to 02, however in the 4.7.1 firmware and later the UAA address will be converted to LAA
Separate MGMT Interface MAC in 4.7.1 final release and newer NAT UAA->LAA conversion The example of the conversion please find below

Universally administered addresses (UAA) to locally administered addresses (LAA) conversion logic:
Locally administered addresses are distinguished from universally administered addresses by setting (assigning the value of 1 to) the second-least-significant bit of the first octet of the address. This bit is also referred to as the U/L bit, short for Universal/Local, which identifies how the address is administered.

UAA

HEX 1st octet Binary
BC:E6:7C:AA:BB:C1 BC = 10111100

LAA

HEX 1st octet Binary
BE:E6:7C:AA:BB:C1 BE = 10111110

Thank you.

Will that break existing implementations, and/or, existing networks that rely on NAT mac addresses to assign static IP addresses with DHCP?

Good point. We will keep the current logic in 4.7.1 and newer releases.

Thanks.

1 Like

I’m having some trouble converting certain mac addresses using this info.

If I have a force 300 with the mac address 58:c1:7a:xx:xx:xx how would this convert for the seperate management interface

I’ve tried using LAA and starting it with 5A and using UAA and starting with 02, neither worked. I also tried 52 just to see, but this also didn’t work.

I figured it out, the correct mac is 3A:C1:7A:xx:xx:xx

2 Likes