AR750 (W)WAN MAC addresses

Technical Support for Routers
1

Please help me understand……

I just bought an AR750, which I want to use in WISP / Router mode

It is running the latest software I could find, 3.026.

When I select More Settings - MAC clone it shows me a default Your Router (WAN) MAC address xx:xx:xx:xx:xE:74. This address is also found on the sticker on the bottom of the device.

When I connect the router wireless to my home router however it uses MAC address xx:xx:xx:xx:xE:76

When I use the More Settings - Advanced - Network - Interfaces screen I see that MAC address xx:xx:xx:xx:xE:76 is actually the WWAN interface

Now I expected that the WAN interface would be used connect to the host router and that the WWAN interface would be serving the clients behind the NAT firewall. This would be in accordance with what is specified in the MAC clone box and the sticker on the device.

So it seems to me that WAN and WWAN MAC addresses are swapped.

Is this how it is supposed to be? Or am I just misunderstanding things?

Thank you for your advice,

Best regards,

Herman.

2

wwan is for your WISP repeater. So if you clone Mac address, it will use for both WAN and WWAN.

If you want to change the Mac address of its own wifi, you may need to do this in advanced->network->wireless

3

Dear alzhao,

Thank you for your almost immediate answer!
Such a response time is really impressive.

I am trying to wrap my brain around this subject, but I still don’t get it.

What I would like to do is to use the default MAC address as stamped on the sticker and found in the MAC clone box to connect to my home router.
How would I do that, what action do I have to take?

Thank you again for your time,

Best regards,

Herman.

4

In most cases, the MAC address used is immaterial, as long as there are no conflicts with another MAC on the same subnet. MAC-address cloning (changing) is primarily for users that have an ISP that “registers” a specific MAC address for their subscriber’s equipment and won’t connect to anything else.

The MAC address for the wireless, if you don’t modify the settings, will be repeatable. If, for some meaningful reason, you need to set it for your upstream wireless, I would just use what you see, the …:76 address, as I understood your post.

Perhaps a side note, or perhaps meaningful, is that MAC-address filtering provides virtually no additional security. As you can see, they can be trivially changed and are “visible” to anyone, without connecting to your wireless network.

5

I understand what you are saying, and it is probably the most pragmatic approach to just accept the MAC address the router is offering upstream.

Nevertheless I find it very strange that the router advertises a default MAC address in the MAC clone box that is not being used.

Only when I actually clone the address of my phone or tablet the content of the MAC clone box is communicated to the upstream router, which is what is supposed to happen of course.

I would consider this a software glitch, but nothing that stops me from using the device.

6

This confuses me – the upstream router doesn’t set the MAC of its clients.

Reading target/linux/ar71xx/files/arch/mips/ath79/mach-gl-ar750.c tells me that the MAC address is set from on-flash data

#define GL_AR750_MAC0_OFFSET            0
#define GL_AR750_WMAC2G_CALDATA_OFFSET  0x1000
#define GL_AR750_WMAC5G_CALDATA_OFFSET  0x5000
[...]
        ath79_init_mac(ath79_eth0_data.mac_addr, art + GL_AR750_MAC0_OFFSET, 0);
        ath79_init_mac(ath79_eth1_data.mac_addr, art + GL_AR750_MAC0_OFFSET, 1);
        ath79_register_wmac(art + GL_AR750_WMAC2G_CALDATA_OFFSET, NULL);

Now, which one is the “label” MAC I’d have to check, but the MACs are deterministic, and set at the factory.

The behavior in the newer ath79 port, submitted as [OpenWrt-Devel] ath79: add support for gl-ar750 - Patchwork, is the same.

7

I am sorry, not an native English speaker here…
I meant to say the MAC address the AR750 is offering to the upstream router.

Which probably means there is no chance a user can alter it?

1 Like
8

You can alter it in /etc/config/network, or by using LuCI to change it (which changes that file).

That code is what sets the “right” values when the device boots.

MAC addresses are generally assigned to a specific manufacturer. That manufacturer assigns a different set of them to every device they make. That way there are never duplicates.

9

Thanks! I will edit the addresses there tomorrow (it is close to midnight over here now), will come back then.

1 Like
10

Just to help clarify things a little bit here, for your information sake.
The reason that the MAC address printed on the bottom sticker of the device is different from the Wireless MAC you are seeing is that technically they are two different interfaces. That is, the MAC printed on the sticker is the one GLI assigned to the physical WAN port on the unit.

Typically on these types of devices if you look closely you will see a number of MAC addresses by default:

  1. First one for the physical WAN port
  2. Second for the LAN interface/wired ports
  3. Third for the Wireless radio (2.4Ghz)
  4. Fourth for the other Wireless radio (5Ghz)

These are populated by the code that @jeffsf mentions in post #6 above. Most manufacturers make them sequential. So if you’re familiar with HEX, in your case they read:

  1. Physical WAN Port - xx:xx:xx:xx:xE:74
  2. LAN Ports - xx:xx:xx:xx:xE:75
  3. Wifi 2Ghz Radio - xx:xx:xx:xx:xE:76
  4. Wifi 5Ghz Radio - xx:xx:xx:xx:xE:77

Without getting into the whole specifics of how networking actually works, the idea of MAC addresses is that they give a physical interface a unique identifier on the local network. As @jeffsf pointed out, you can change that arbitrarily if you want (though there’s no real reason to), but it doesn’t achieve much. You may also introduce problems if you are not careful, because if you end up manually assigning the same MAC address to more than one interface then theoretically other devices on the network may get confused as to how to actually communicate with your router. (From the description of your setup it doesn’t sound like this would happen, but I wanted to point it out.)

1 Like
11

Changing the MAC may actually cause “unexpected behavior” in the future, as there are tree-wide changes afoot to identify the interface that is assigned to the “label MAC address” in the DTS for run-time access.

While the applications haven’t been fully defined yet, my strong suggestion would be to not change MAC addresses unless that is the only way your ISP will let you connect to them, or you have a compelling reason, such as preserving a DNS-registered public IP an IA_PD when changing out the router to which you connect to your ISP (which would cause you to have to modify firewall rules and reassign dozens of IPv6 addresses on dozens of machines and in DNS).

12

@jeffsf and @jolouis

Thank you both so much for your patience with me and for your time!
I am beginning to understand what caused my confusion about this default MAC address in the clone box.

My Pi-hole identifies the radios as IEEE Registration Authority devices. It is what they look-up in a MAC-database. Usually it says something like Microsoft Corporation or Apple, inc. Probably some registration hiccup.

Thank you for your advise. I listened to it, left the assigned addresses alone.

As far as I can see in LuCi there are only three MAC addresses involved in this device.

  1. WAN / WAN6, xx:xx:xx:xx:xE:74. It is the address used when I connect the device wired to my router.
  2. radio0, the 5 GHz device, xx:xx:xx:xx:xE:75
  3. radio1, the 2,4 GHz device, xx:xx:xx:xx:xE:76

I have seen both radios connecting to my upstream router (obviously not at the same time).
So, when I return to my opening post, the MAC clone selection box gives me a choice of either xx:xx:xx:xx:xE:74 or the MAC of the connected device (phone, tablet) to clone, whereas in reality it uses xx:xx:xx:xx:xE:75 or xx:xx:xx:xx:xE:76 to connect as long as I don’t give it something to clone.
Oh well…