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What does an IP address look like?

In order to access commercial e-resources, subscribing institutions must provide vendors with their external/public IP address/es as these are used to access the internet.  


The most basic format includes a simple set of 4 blocks of numbers with a minimum of 0.0.0.0 and a maximum of 255.255.255.255 (although neither of these are valid for use for commercial e-resources).


A typical IP address would look like this: 122.140.201.66


IP addresses can also be shown as a range, for example:     122.140.201.66-144 or 122.140.201-205.* (* represents 0-255)


IP addresses can also be shown in CIDR format for example:


122.140.201.0/24 (this represents 122.140.201.*)


For many institutions, the external/public IP address is the address of the proxy server (see Wikipedia entry).


Individual computers which are part of an institutional network may have internal/private IP addresses linking them to the proxy server.  Internal/private IP addresses are not visible on the internet so cannot be used to gain access to commercial e-resources.


The following are examples of internal IP address ranges:


10.0.0.0 – 10.255.255.255 (CIDR = 10.0.0.0/8)


172.16.0.0 – 172.31.255.255 (CIDR = 172.16.0.0/12)


192.168.0.0 – 192.168.255.255 (CIDR = 192.168.0.0/16)