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Having following routing table on Windows 7:

Network Destination       Netmask           Gateway         Interface    Metric  
127.0.0.0                 255.0.0.0         On-link         127.0.0.1    306  
127.0.0.1                 255.255.255.255   On-link         127.0.0.1    306

What does the second entry (starting by 127.0.0.1) mean? Is it necessary? I haven't seen it in many other examples in the net.

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127.0.0.1 is localhost, aka your own machine. If is very common. I would almost say 127.0.0.1 and ::1 are always present is you loaded IP networking.

Having a loopback network interface like this allows people to use a common design where you always use the network, even on a computer without any physical network card.

Note that any IP from the 127.0.0.0/8 range is meant to be local.

I haven't seen it in many other examples in the net.

Possibly because it always already is there. For Linux you cannot build a kernel with networking without the loopback interface. It is hardcoded to be the first network interface. I remember somethign similar for windows were 127.1 was hardcoded in DLLs. No need to manually add this. No need to mention it in documentation.

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