While MAC addresses are 48 bits, that is a lot more than the 32 bit IPv4 adresses (even counting the reserved addresses 255, 127, Class D Multicast etc ), will we not eventually run out of them?

Also, IPv6 addresses may be derived from the 48 bit MAC addresses. And IPv6 address space is much larger than the MAC address space. So will we not end up with IPv6 addresses without any MAC address to associate with? Or is there an official plan to duplicate MAC addresses?

Also, are bluetooth MAC addresses in the same space as Ethernet mac addresses?


1) Not in your, mine, or our grand-childrens lifetime. Every grain of sand in the planet would use a microscopic percentage of the available address space.

In fact, assuming the most number of grains of sand - around 10^24 - 294 femtopercent (yes, femto, 10^-15) would be used if every grain were allocated an IP. You could allocate 340 billion planets with the same number of grains of sand before you even came close to filling up the address space. After all that, you'd still have 2.8x10^35 addresses free.

That's why your ISP will give you around 4722366482869645213696 addresses by default (give or take a few)

2) They can be derived from your MAC, yes. But remember MAC addresses are not just for TCP/IP - I could run IPX/SPX or NetBUI over ethernet too. But in theory yes, you would run out of MAC addresses before IPv6 addresses. But you could also assign 1 trillion IP addresses to a single MAC address too.

3) Yes

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    And MAC addresses are only used as part of SLAAC auto configuration. There are still Privacy Extensions that don't rely on the MAC Address, and DHCPv6 Assigned addresses, and you can manually assign addresses. MAC Addresses are only a small part of the addressing scheme. – fukawi2 May 24 '13 at 4:53

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