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I have always noticed an IP something "169.254.x.x" attached even when I am not connected to any network in my Windows operating system.

In Linux, when I list my routing table.

$ ip route show 

I get an entry like

169.254.0.0/16 dev eth0  scope link  metric 1000 

Can somebody explain me what is this ip actually. Whether its something like the 127.0.0.0/8 family.

Edit: In ec2, each instance can get meta-data regarding their own by making HTTP requests to this IP.

$ curl -s http://169.254.169.254/user-data/

So can someone tell me to whom this ip is actually assigned ?

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3 Answers 3

These are dynamically configured link-local addresses. They are only valid on a single network segment and are not to be routed.

Of particular note, 169.254.169.254 is used in Amazon EC2 and other cloud computing platforms to distribute metadata to cloud instances.

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So can u tell me that 169.254.169.154 is assigned to whom in ec2. –  pradeepchhetri Sep 13 '12 at 10:04
    
The blue text means a link that you can click on for more information. Please do so. –  Michael Hampton Sep 13 '12 at 10:06
    
But there is nothing mentioned to whom this ip is assigned to ..regarding the internals in terms of virtualization. –  pradeepchhetri Sep 13 '12 at 10:13
    
That address is not a public address, it is in the same scope as 10.x.x.x, 192.168.x.x etc, many people around the world could have this address, it is private. –  Alex Berry Sep 13 '12 at 10:14
1  
@pradeepchhetri It's not assigned to anyone. It's a special-use address. –  Michael Hampton Sep 13 '12 at 10:18

In almost all circumstances that's a IP assigned automatically by an interface that's set to get its IP via DHCP but can't get one.

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It's a IPv4 link local address, as defined in rfc3927. Usually ZeroConfig/Bonjour/mdns et al enabled boxes are setup to have IPv4 ll address to enable (home) networking without the presence of an DHCP or unicast DNS server.

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