U:1500 Metric:1 RX packets: 193321787 errors:0 dropped:0 overruns:0 frame:0 TX packets: :196670319 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen: 1000 RX bytes 3569684877 (3.3 GB) TX bytes:3127898656 (2.9 GB) Interrupt:16 Here is a similar result from a Cisco router. First the MAC address from the interface: R1#sho int fo/o I inc Hardware Hardware is MV96340 Ethernet, address is 0012.43b9.2c70 (bia 0012.43b9.2c70) And here is the automatically configured link-local address: R1#sho ipv6 interface fo/o I inc link-local IPv6 is enabled, link-local address is FE80::212:43FF: FEB9: 2C70 In the link-local address, you can see the same leading 2 resulting from the flipped bit, and the FF:FE in the middle of the MAC address. Subnetting Because the first 48 bits are reserved for Internet routing, you will likely never have to deal with masks larger than /48 unless you work with Internet routing tables and ag- gregation. Since the next 8 bits are reserved for subnetting, you will have access to 65,535 subnets with over 18 quintillion devices per subnet for each /48 allocated. Now that's cool and all, but do I need to allocate 18 quintillion addresses for each point- to-point link? Need is not really the right word. You don't need to, but you really should. There are a couple of good reasons why. First off, we've grown SO accustomed to trying to limit IP address usage that using only the bare minimum has become second nature. Why use 256 IP address on a point-to- point link when you only need 4? This thinking has saved us in the past, and habits, especially good ones, are hard to break. The fact remains that there are SO many IPv6 addresses that we won't hit the wall for a long, long time. How long? Long after Skynet and the terminators destroy human civilization as we know it. There are protocols that require IPv6 addresses to be 64-bits, Stateless Address Auto- configuration being the most commonly quoted. That means your subnet mask should never be smaller than /64. In fact, all IPv6 networks in common 