Difference between global IP address and Local IP address?


A global IP address is assigned to a computer or modem by an internet service provider and can be communicated with from anywhere on the internet. Global IP addresses are unique and assigned only to a single computer or device.

Local IP addresses (Private IP Addresses) are assigned by a router and include 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255 and 192.168.0.0 to 192.168.255.255. Local IP addresses can only be used to communicate within a closed network.

As an example:

 

  • Bob’s house has two computers and a router.
  • ** Bob is assigned an IP addresses of 78.182.2.17 by his ISP.
    • Both of bob’s computers are connected to a router which is connected to the internet.
    • *** Router IP:
      • **** Local: 192.168.0.100
        • Global: 78.182.2.17
      • Computer one IP: 192.168.0.101
      • Computer two IP: 192.168.0.102

When Bob uses either computer one or two to connect to the internet the traffic is passed by the IP address 78.182.2.17 which is his global IP address. The router acts as a gateway to the internet using this IP address.

Bob can however communicate between his two computers within his house using the 192.168. IP addresses.

If someone on the internet want’s to communicate with Bob they use 78.182.2.17 and the router determines which of Bob’s two computers the traffic is intended for as the 78.182.2.17 IP address in this case is actually Bob’s router and is not directly assigned to either computer.

Local IP addresses must be unique within a network but individual networks can use the same internal IP addresses provided they are not connected. (ie. Company A can only have one 10.0.11.23, however company B can also have a 10.0.11.23)

 

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