2 ms·

> Surely the uniqueness is only required at the bottom end of the stack before the first 'router' ie the cell tower Not if you need to send a message to $that

> Surely the uniqueness is only required at the bottom end of the stack before the first 'router' ie the cell tower Not if you need to send a message to $thatUniquePhone. Over simplifying considerably, but if a land line places a call to a mobile, the "220-1234 calling for 220-7890" message enters the network. The `220-7890` phone number needs to map to the unique modem address so you can look up which tower the call setup data should be sent to. If - by sheer coincidence - I also have your MAC address and am attached to a tower 3 states away... which tower(s) do you forward the call setup data to?!

vdqtp3 2y ago
> which tower(s) do you forward the call setup data Whichever one has most recently communicated with the user in question (based on the credentials or certificate provided, in the original example)
kbolino 2y ago
Assuming something like VoIP is in use, you reach other devices with their IP addresses, not MAC addresses.
- thaumasiotes 2y ago
  As far as I know MAC addresses are never used to route a message to a particular recipient. They're used so that devices that overhear the message, but aren't the intended recipient, can ignore that message on the honor system. If you have a wired connection, this makes the MAC completely superfluous. The concept is sort of still valid for wireless connections (or of course for "wired" connections where you have multiple devices physically connected by the same wire, a bus, where the concept originated). It should be rethought.
  - kbolino 2y ago
    A typical Ethernet switch operates only at layer 2 and so does indeed route frames by MAC. You need a more expensive, typically managed, switch in order for it to use layer 3 addresses instead and, even then, the initial setup usually relies on layer 2 routing to get an IP address before layer 3 routing can take over. As a sibling comment points out, the whole stack would/does need a rethink to work differently than this. IPv6 SLAAC as mentioned before can potentially eliminate the need for layer 2 addresses but a lot of networks are still IPv4-only, dual-stack, or even layer 3-agnostic. Note that this is only about last-mile/first-hop. Once you scale past a single LAN segment, routing is mostly layer 3 until you get to core Internet infrastructure which uses ASNs and BGP. At the very least, it is probably sufficient to say that routing across a WAN is all about IP, but if you zoom in on parts of that network of networks, the underlying technologies often use other routing mechanisms internally that don't get exposed to the other parts of the WAN.
  - londons_explore 2y ago
    Yes - the whole MAC/ARP/IP parts of the typical IP stack are a legacy mess and should be sorted out.

vdqtp3 2y ago

> which tower(s) do you forward the call setup data Whichever one has most recently communicated with the user in question (based on the credentials or certificate provided, in the original example)

kbolino 2y ago

Assuming something like VoIP is in use, you reach other devices with their IP addresses, not MAC addresses.

thaumasiotes 2y ago
As far as I know MAC addresses are never used to route a message to a particular recipient. They're used so that devices that overhear the message, but aren't the intended recipient, can ignore that message on the honor system. If you have a wired connection, this makes the MAC completely superfluous. The concept is sort of still valid for wireless connections (or of course for "wired" connections where you have multiple devices physically connected by the same wire, a bus, where the concept originated). It should be rethought.
- kbolino 2y ago
  A typical Ethernet switch operates only at layer 2 and so does indeed route frames by MAC. You need a more expensive, typically managed, switch in order for it to use layer 3 addresses instead and, even then, the initial setup usually relies on layer 2 routing to get an IP address before layer 3 routing can take over. As a sibling comment points out, the whole stack would/does need a rethink to work differently than this. IPv6 SLAAC as mentioned before can potentially eliminate the need for layer 2 addresses but a lot of networks are still IPv4-only, dual-stack, or even layer 3-agnostic. Note that this is only about last-mile/first-hop. Once you scale past a single LAN segment, routing is mostly layer 3 until you get to core Internet infrastructure which uses ASNs and BGP. At the very least, it is probably sufficient to say that routing across a WAN is all about IP, but if you zoom in on parts of that network of networks, the underlying technologies often use other routing mechanisms internally that don't get exposed to the other parts of the WAN.
- londons_explore 2y ago
  Yes - the whole MAC/ARP/IP parts of the typical IP stack are a legacy mess and should be sorted out.