Is there some MAC address value, that can be used to denote that device does not have MAC set (something like 0.0.0.0 for IP).? I thought of ff:ff:ff:ff:ff:ff, but afraid that it could be meaningful when set for interface.

The question is how to state the fact that specific interface does/should not have MAC - if i cannot just leave the field empty (in docs, such a restriction) what value should I use.? For ip i can specify 0.0.0.0 for that purpose.

Lets take the following TR-098 parameter: InternetGatewayDevice.WANDevice.{i}.WANConnectionDevice.{i}.WANPPPConnection.{i}.MACAddress - its value is required to be either empty (n case of PPPoA) or contain mac of underlying device (if PPPoE). But in my case empty value cannot be specified - i have to give some MAC.

closed as off-topic by Ron Maupin May 29 at 15:11

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    Why would a device not have a MAC address set? What's the real problem you're trying to solve here? – Teun Vink May 29 at 8:28
  • PPPoX for instance. – Green Tree May 29 at 8:54
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    MAC addresses are called BIA (Burned-In Addresses) for a reason. Each interface will have one from the manufacturer. – Ron Maupin May 29 at 14:11
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    Some LAN protocols use MAC addresses. Those are the IEEE LAN protocols (ethernet, Wi-Fi, token ring, etc.). Some use 48-bit MAC addresses, and some use 64-bit MAC addresses. Other protocols (frame relay, ATM, PPP, etc.) do not use MAC addresses. Some use something else (DLCI, VPI/VCI, etc.), and some (PPP, etc.) use no addressing. It makes no sense to use MAC addresses on a protocol that doesn't have MAC (Media Access Control). – Ron Maupin May 29 at 14:30
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    No, a PPP interface would never have a MAC address because PPP doesn't use any addressing (there being only two endpoints, it doesn't need it). The ethernet hardware interface will have a MAC address assigned by the manufacturer. An ATM hardware interface will not. What you are asking makes no sense. – Ron Maupin May 29 at 14:41

Ethernet across switches doesn't work without a valid MAC, no matter what you do on top.

With a dedicated point-to-point link you can do whatever you want if both sides are fine with it. However, Ethernet is not a simple serial line. PPoX requires its special Ethernet variant PPPoE in order to work on Ethernet (unless you build your own, similar variant) because Ethernet is not point-to-point.

An IP address of 0.0.0.0 is only used for very special cases (esp. address probing in DHCP) when addressing is ensured by the underlying layer (usually Ethernet). Ethernet has nothing else to rely on, so an "empty" MAC address simply won't work.

However, if you require a temporary MAC address for some time you can freely use any locally administered address: set the two least significant bits in the MAC address's first octet to 10 and simply make sure the address is unique within your network.

  • why are you answering about ethernet, why switches, not dslam.? the question is how to state fact that specific interface does/should not have MAC - if i cannot just leave the field in, say, docs empty, (such a restriction) what value should I use.? For ip i can specify 0.0.0.0.0 for that purpose. I'M NOT GOING TO ASSIGN such address to interface actually. – Green Tree May 29 at 12:07
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    I'm not clairvoyant and can't simply know what your question is about unless you include the details. The standard use of Ethernet is across switches. A DSL modem usually uses Ethernet. A DSLAM can use just about anything (Ethernet, ATM, ...) and you gave no hint into that direction. If you're not using Ethernet you might not need a MAC but unless you provide specific details no one will be able to answer that question. – Zac67 May 29 at 12:16

I am not sure what you are trying to do. MAC Adresses are essential for communicating in a network like ethernet. ff:ff:ff:ff:ff:ff is a so called Broadcast MAC Adress, which means that a ethernet frame with destination MAC of ff:... will be send to every station in a switched network. Even for PPPoE for example, you need correct MAC adresses for the communication of the underlying ethernet.

  • No. I'm asking about some value like 0.0.0.0 for IP - for instance if you set 0.0.0.0 for interface with ifconfig it ip address would be reset, related routes reconfigured, etc. And PPP is not related to MAC - it can be encapsulated not only in ethernet, and underlying layers are not forced to have ethernet. – Green Tree May 29 at 9:50
  • Maybe I am not understanding what you are going to do. Please be more specific. Show please an example of your ppp config. A diagram of your setup would also be fine. On a physical Interface for MAC based Networks you are not able to empty or delete the MAC address. – Winnie Tigger May 29 at 11:40

AFIK mac addresses can't be a matter of negotiation like ip addresses. However like already mentioned there are magic destination mac addresses like FF:FF:FF:FF:FF:FF intended to be received by all lan network participants.

For negotiation of ip addresses the usage is somehow like: "Is there anybody out there who can give me an ip address ...."

Learning switches typically repeat broadcast frames on all oher ports. this is why nowadays with a network analyzer like wireshark you see only communication between your and other devices plus broadcast frames.

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