3 ms·

A MAC address is needed to bootstrap IP, even if non-routable - and because we don't want to bootstrap MAC addresses, we just assign them statically. From the v

A MAC address is needed to bootstrap IP, even if non-routable - and because we don't want to bootstrap MAC addresses, we just assign them statically. From the very beginning (oversimplifying a bit, but I digress), a MAC has really just been the key in a hashed map from MAC to switch port. You _could_ design a system where MAC addresses were always randomized, but this technology evolved at a time where processing power and the bandwidth of your switches likely might have struggled with the additional load. If we were designing a system from scratch it would probably make sense for everything to have hierarchical, switch-local identities that were cheap to allocate and check and put a bit more extra routing storage in the switch chips to efficiently route these.

themafia 1y ago
> a MAC has really just been the key in a hashed map from MAC to switch port. Until you consider broadcast/multicast traffic.
Polizeiposaune 1y ago
In the very beginning of ethernet there were no switches - you just had a bunch of transceivers connected to a length of coax cable. Every NIC on the wire saw every packet; the destination mac address indicated whether the packet was interesting enough to each node to be worth putting a copy in host memory and bothering the CPU to look at.
- kstrauser 1y ago
  For the young’uns amongst us: switches use to be an expensive luxury. Most small LANs used cheap hubs at the edges, where every inbound Ethernet frame was sprayed out to all the other ports. They commonly had “collision” lights, and they used ‘em.
  - eszed 1y ago
    Yup. Was going to say the same thing. I remember my first encounter with a switched network bent my brain. What, I have to give everything an address? Where'd this 192.168 come from? Networking used to be so easy! Anyway, we all learned and adapted.
windexh8er 1y ago
> A MAC address is needed to bootstrap IP... This is fundamentally incorrect. IPv4 for LAN, sure - but "bootstrap" it is not. There's plenty of L2 that have no MAC: PPP, ATM, Frame Relay, etc. Also, MACs aren't needed for IPv6. ND works without MAC in v6. And, finally... There's no MAC for loopbacks.
- chasing0entropy 1y ago
  None of those l2 protocols can traverse a wan without an encapsulation layer which always requires an address or link to the physical layer.
  - immibis 1y ago
    Sure they can - a WAN is the same as a LAN, but bigger. However, that comes with different tradeoffs, in particular the need to reduce bandwidth by using less chatty protocols. But you can absolutely rent a fiber between two buildings in the same city and run Ethernet on it.

themafia 1y ago

> a MAC has really just been the key in a hashed map from MAC to switch port. Until you consider broadcast/multicast traffic.

Polizeiposaune 1y ago

In the very beginning of ethernet there were no switches - you just had a bunch of transceivers connected to a length of coax cable. Every NIC on the wire saw every packet; the destination mac address indicated whether the packet was interesting enough to each node to be worth putting a copy in host memory and bothering the CPU to look at.

kstrauser 1y ago
For the young’uns amongst us: switches use to be an expensive luxury. Most small LANs used cheap hubs at the edges, where every inbound Ethernet frame was sprayed out to all the other ports. They commonly had “collision” lights, and they used ‘em.
- eszed 1y ago
  Yup. Was going to say the same thing. I remember my first encounter with a switched network bent my brain. What, I have to give everything an address? Where'd this 192.168 come from? Networking used to be so easy! Anyway, we all learned and adapted.

windexh8er 1y ago

> A MAC address is needed to bootstrap IP... This is fundamentally incorrect. IPv4 for LAN, sure - but "bootstrap" it is not. There's plenty of L2 that have no MAC: PPP, ATM, Frame Relay, etc. Also, MACs aren't needed for IPv6. ND works without MAC in v6. And, finally... There's no MAC for loopbacks.

chasing0entropy 1y ago
None of those l2 protocols can traverse a wan without an encapsulation layer which always requires an address or link to the physical layer.
- immibis 1y ago
  Sure they can - a WAN is the same as a LAN, but bigger. However, that comes with different tradeoffs, in particular the need to reduce bandwidth by using less chatty protocols. But you can absolutely rent a fiber between two buildings in the same city and run Ethernet on it.