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I've been reading about VLANs recently and how switches have the ability to modify ethernet frames by inserting/removing VLAN tags. This got me thinking, would we ever update the Ethernet standard such that hosts do not need to include their source/dest MAC address in each message in order to save bandwidth?

For example, imagine I'm a host plugged into a switch. If I were to let the switch know my MAC address on start-up, I could then just have the switch tag my MAC address onto all future messages I send out. That saves me time from having to send 6 bytes for each message.

Similarly, if I'm now receiving messages. The switch is smart enough to only send me messages that are addressed to me. So I really don't need to check the dest address since I have confidence in my switch to only send me messages that are addressed to me.

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    What if there is a hub, other switch, or host with multiple MAC addresses connected to the switch interface? That is common enough. Join the IEEE to propose your solutions, but such speculation is off-topic her. This is not a discussion forum, and questions seeking primarily opinion-based answers are off-topic. Commented Nov 16, 2024 at 15:57
  • @RonMaupin, yes I neglected the case where multiple MACs can be on a single port so you are correct. You gave me a technical answer to my question. I don't believe my question was off topic, if anything, the I phrased the title so it might have appeared that way by referring to "standards". However, it was more about the technical feasibility. Commented Nov 16, 2024 at 16:04
  • (sigh) NO. This is yet another hair-brained scheme from someone who does not understand what they're trying to change. SRC/DST MAC's exist at layer-2 for a reason. (there is an infinity of edge cases you're ignoring or are simply unaware of.) Read all of the questions w.r.t. doing away with IP "because we have MACs". (also, those 6 bytes are about 0.4% of an ethernet frame.) Commented Nov 16, 2024 at 16:14
  • @Ricky, Hair-brained scheme or a question from someone new to the topic? :) Commented Nov 16, 2024 at 16:25

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This got me thinking, would we ever update the Ethernet standard such that hosts do not need to include their source/dest MAC address in each message in order to save bandwidth?

No, not possible. Ethernet switches require proper addressing information to forward Ethernet frames. The destination is used for direction and the source for updating the switch's MAC table.

I'm a host plugged into a switch. If I were to let the switch know my MAC address on start-up, I could then just have the switch tag my MAC address onto all future messages I send out.

This ignores the possibility that another switch is connected, with multiple MAC addresses behind it. Your approach for 'saving bandwidth' would require an explicit protocol for updating all MAC addresses in the network.

The switch is smart enough to only send me messages that are addressed to me.

That's the exact purpose of the destination MAC address in a frame. How else would a switch know where a frame is supposed to go? If the switch is supposed to use IP addresses instead, forwarding by IP address is what a router does. Remember that Ethernet transports more than just IP traffic.

Somewhat related question: Why do we still use Ethernet?

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  • You bring up a good point that multiple MACs can be behind the same switch port. That pretty much ruins the idea. However, assuming that wasn't the case. The expectation is that sources would only need to tag the dest address on each ethernet frame since switch could fill out the src (again assuming one MAC address per port) Commented Nov 16, 2024 at 16:00
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    A single switch is only sufficient for a small network - switches need to be able to connect to each other. And Ethernet's success is largely due to its simplicity and universality (along with low cost). Different host and interlink protocols would kill that. Commented Nov 16, 2024 at 17:29
  • Also, just because you are talking to a host, doesn't guarantee that you'll only see one MAC. Technologies like bridged hypervisor virtual NICs can result in one physical host NIC sending and receiving traffic with multiple MACs. Commented Nov 17, 2024 at 23:14
  • @user1937198 I was considering mentioning shared management ports, virtual switches, or virtual MACs but decided to keep it simpler. ;-) Commented Nov 18, 2024 at 6:35

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