Non-Routable Address Space

The IPv4 standard does not support enough IP addresses for every person, i.e., IPv4 addresses are now depleting. To prevent IPv4 exhaustion, in 1996, RFC1918 was published (Request for Comments), it outlined networks that are can be used by anyone within an autonomous system and are known as Non-Routable Address Spaces.

Ranges of IP addresses defined by RFC1918 are –

• 10.0.0.0/8 ( Range: 10.0.0.0 – 10.255.255.255 )
• 172.16.0.0/12 ( Range: 172.16.0.0 – 172.31.255.255 )
• 192.168.0.0/16 ( Range: 192.168.0.0 – 192.168.255.255 )

These IP addresses are reserved for private networks, interior gateway protocols will route these address spaces within network. Non-routable address space allows for nodes to communicate with each other on same network. Since every computer need not be connected to every other computer on Internet, non-routable address spaces can be used locally in various private networks.

Even if computer has to communicate to another computer, not on the same network, Network Address Translation (NAT) is used, in which one or more local IP address is translated into one or more Global IP address. Non routable address spaces are in use today because of technologies like NAT. Till IPv6 becomes the solution of exhaustion of IPv4 addresses, non routable address spaces and NAT will help in preventing collisions of IP addresses around the globe.

Advantages :

1. It helps in conserving IPv4 address space.
2. Extra layer of security, since these networks cannot be accessed by exterior gateway routers. So, network is safe from malware and viruses.
3. Data protection and privacy- Since data can be accessed only inside network. It is good for small businesses that handle lot of data and sensitive information.

Disadvantages :

1. End to end IP tracing gets lost. It gets difficult to troubleshoot your network from remote site.
2. Isolation : Nodes inside private network are not reachable by nodes outside the network.
3. Private networks have higher maintenance requirements, because of non-standard configurations and setups for the network interface.

Private IP networks are used by organizations where security and data privacy are important over public IP addresses. Now-a-days, non-routable address spaces and NAT are being preferred to save IPv4 address space because IPv4 addresses are now depleting.