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This could be a no-brainer, but when I look in ifconfig it lists two different global IPv6 addresses. Is there a reason why I'm getting two assigned? Shouldn't I just get a single address?

valorin@gandalf:~$ ifconfig
eth0      Link encap:Ethernet  HWaddr e8:9a:8f:6d:6a:aa  
          inet addr:172.10.10.1  Bcast:172.10.10.255  Mask:255.255.255.0

          inet6 addr: 2400:4000:cafe:2014:48c8:f262:ebe8:297b/64 Scope:Global
          inet6 addr: 2400:4000:cafe:2014:ea9a:8fff:fe6d:6aaa/64 Scope:Global

          inet6 addr: fe80::ea9a:8fff:fe6d:6aaa/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:258 errors:0 dropped:0 overruns:0 frame:0
          TX packets:313 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:78280 (78.2 KB)  TX bytes:46173 (46.1 KB)
          Interrupt:41 Base address:0xe000 
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Don't use ifconfig, use ip addr instead. –  Michael Hampton Feb 1 at 1:57

1 Answer 1

up vote 27 down vote accepted

The address containing ea9a:8fff:fe6d:6aaa is an automatically configured address based on your Ethernet MAC address. You can recognize them because they contain ...ff:fe... in the middle of the last 64 bits. The rest of the bits is derived from your MAC address. Compare

ea9a:8fff:fe6d:6aaa

with

e8:9a:8f:6d:6a:aa

Because some people are worried that making your MAC address visible on the internet would cause content / website providers to track your behavior by your mac address (and such behavior wouldn't surprise me, although they can more easily track you with cookies, browser-local storage etc etc etc) the privacy extensions were introduced.

The address containing 48c8:f262:ebe8:297b is such an address. That is the address that will be used to connect to websites and other outgoing connections. It will change over time to maintain your privacy and make you harder to track.

Both addresses are available for you to use. Outgoing connections will use the privacy address, unless configured otherwise. You can also still receive incoming connections on the MAC address based IPv6 address. This is all done to give you lots of flexibility. If you want you could add even more addresses.

PS: another tool to see IPv6 addresses is

ip -6 addr

It will show you a bit more detail. You will see the word temporary after the privacy address, which indicates what it is.

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Exactly what I was after, thank you! –  Valorin May 24 '12 at 22:28

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