Private network

Author: Leandro Alegsa Creation date: November 13, 2022

In Internet terminology a private network is typically a network that uses private IP address space, following the RFC 1918 standard. Computers may be allocated addresses from this address space when it is necessary for them to communicate with other computing devices on an Intranet network (internal private computer network that uses the Internet Protocol).

Private networks are quite common in home and office local area network (LAN) designs, as many organizations do not see a need for globally unique IP addresses for every computer, printer and other devices that the organizations use. Private IP addresses were created due to the shortage of publicly registered IP addresses created by the IPv4 standard. One of the reasons IPv6 was created is to overcome this limitation of the IPv4 standard. However IPv6 still did not achieve a widespread use.

Routers on the Internet should be configured to discard any packets containing private IP addresses in the IP packet header. This isolation gives private networks a basic form of security as it is not usually possible for the outside world to establish a connection directly to a machine using these private addresses. As connections cannot be made between different private networks via the internet, different organizations can use the same private address range without risking address conflicts (communications accidents caused by reaching a third party using the same IP address).

If a device on a private network needs to communicate with other networks, a "mediating gateway" (in-between gateway) is needed to ensure that the outside network is presented with an address that is "real" (or publicly reachable) so that Internet routers allow the communication. This gateway is typically a NAT device or a proxy server. Public Internet Routers by default will not forward packets with RFC 1918 addresses. Unlike public Internet routers that need additional configuration to forward these packets, internal routers do not need any additional configuration to forward these packets.

This can cause problems, however, when organizations try to connect networks that both use the same private address spaces. There is a potential for clashes and routing problems if both networks use the same IP addresses for their private networks, or if both networks depend on NAT to connect them through the Internet.

Questions and Answers

Q: What is a private network?

A: A private network is a computer network that uses private IP address space, following the RFC 1918 standard. It is typically used for internal networks within an organization or home and office local area networks (LANs).

Q: What was the reason for creating private IP addresses?

A: Private IP addresses were created due to the shortage of publicly registered IP addresses created by the IPv4 standard. One of the reasons IPv6 was created is to overcome this limitation of the IPv4 standard.

Q: How does isolation give private networks security?

A: Isolation gives private networks a basic form of security as it is not usually possible for outside devices to establish a connection directly to machines using these private addresses. Routers on the Internet should be configured to discard any packets containing these addresses in order to provide this protection.

Q: How can different organizations use the same private address range without risking address conflicts?

A: As connections cannot be made between different private networks via the internet, different organizations can use the same private address range without risking address conflicts (communications accidents caused by reaching a third party using the same IP address).

Q: What type of device is needed if a device on a private network needs to communicate with other networks?

A: If a device on a private network needs to communicate with other networks, a "mediating gateway" (in-between gateway) is needed to ensure that outside devices are presented with an address that is publicly reachable so that Internet routers allow communication. This gateway is typically either NAT device or proxy server.

Q: Do public Internet Routers need additional configuration in order to forward packets with RFC 1918 addresses?

A: Public Internet Routers by default will not forward packets with RFC 1918 addresses and require additional configuration in order for them do so. Internal routers, however, do not need any additional configuration in order forward these packets which can cause problems when connecting two separate networks both using similar IP addressing schemes.