- About IP addresses
Most modern networks, including the Internet itself, use a network protocol known as IP. Devices connected to an IP network talk to each other using numbers known as IP addresses. Each device must have an IP address
that is unique on the network to which it is connected. If that network is the public Internet, the IP address must be unique across the whole world. In order to prevent duplication of public IP addresses,
they are recorded and allocated from a global register. In practice, only a small proportion of devices are directly connected to the public Internet. Most are on private networks in homes or offices that connect
indirectly to the Internet through a NAT router. Only the NAT router needs a unique public IP address. The other devices inside a private network share a range of private IP addresses that are reserved
for the purpose.
- IPv4 and IPv6
Even though only a small proportion of devices need registered IP addresses, there are still an awful lot of them. The original IP address scheme, known as IPv4, has some 3.7 billion
possible addresses but demand is so great that we are running out. Concerns about exhausting the pool of IPv4 addresses led to the creation of IPv6, which has a virtually limitless address pool, but adoption
has been slow. Most people, especially providers of consumer equipment and services, prefer to use IPv4 addresses.
- About DNS
IP addresses are long numbers. Humans have a poor memory for long numbers. Some IP addresses therefore have text aliases to make them easier to remember. These aliases are known as "Domain Names".
You are probably familiar with some: "www.amazon.com" and "www.bbc.co.uk", for instance. The technology that converts to-and-fro between IP addresses and Domain Names is known as the
"Domain Name System" or DNS. Reference devices that store and lookup IP addresses that are aliased by a Domain Name are known as "DNS servers". A Domain Name can be thought of as a
pointer to a specific device, as long as that device has a specific IP address. DNS does such a good job of hiding IP addresses that most Internet users do not even know that they exist.
- Dynamic IP addresses
ISPs are each allocated a limited number of registered IPv4 addresses for themselves and their customers. They must manage their pool of IPv4 addresses frugally. Each of their customers needs at least
one IP address when they are connected to the Internet. Most want to use an IPv4 address. Luckily many of them turn off their Internet connection when it isn't being used, which allows their IPv4 address
to be returned to the pool for someone else to use. If a customer reconnects but their previous IPv4 address has been allocated to someone else, they will get a different IPv4 address from the pool.
The process is often referred to as Dynamic IP addressing. It might allow an ISP, for example, to have twice as many customers as they have IPv4 addresses.
- Dynamic DNS
One consequence of Dynamic IP addressing is that a consumer's public IP address might change when they turn on their router. In IT terms, their public IP address is "mutable". Most Internet users
only have outbound traffic and responses, both of which are designed to cope with mutable IP addresses. Inbound Internet traffic is not. A small but growing number of consumers want to access a device inside
a mutable network from a remote location. They face the Catch 22 that they cannot get into the network to discover the new public IP address because they don't know its current IP address. A normal Domain Name
is no help here: it is tied to the current owner of a a specific IP address, which moves around in the case of Dynamic IPs. Dynamic DNS is designed to overcome these issues. It automatically updates the
appropriate Domain Name entries whenever a Dynamic IP address changes, so that it always points to the same device.
- How Dynamic DNS works
Dynamic DNS relies on software on a device inside an Internet connected network that regularly reports its public IP address to a Dynamic DNS server. If the public IP address is different from the DNS reference,
the Dynamic DNS server updates the reference accordingly. The updated information disseminates to other DNS servers through the normal mechanism. In order for this to happen in a timely fashion, Dynamic DNS
Domain Names are usually configured to disseminate every ten minutes rather than the more normal 24 hours. From the outside world a Dynamic DNS Domain Name will always point to the same Internet connected
device, no matter what its public IPv4 address happens to be at any one time.
- What can Dynamic DNS do for me?
Dynamic DNS is for people that want to access a device within a mutable network from a remote location. Typically these devices are within someone's home or small office:
security cameras, Webcams, baby monitors, alarms, smart boxes, tannoys and the like. Demand is growing thanks to the "Internet of Things" which allows all sorts of other
devices to be connected to the Internet. Popular IoT devices include lighting controllers, heating controllers, security controllers and white goods. In future they might include furniture, doors,
windows, curtains and pretty much anything that can have a power source, even if it is only a battery.
- Are there alternatives?
There is an alternative to Dynamic DNS that is known as "Static IPs". A Static IP, exactly as it sounds, is guaranteed not to change. A Static IP that has an associated Domain Name alias will always
point to the same device. Static IPv4 IPs are ubiquitous in business but consumer ISPs need to be more careful with them. Some simply refuse to issue Static IPv4 IPs. Others discourage their use by making
them expensive. It is far easier to get Static IPv6 IPs but they are incompatible with some older and/or cheaper network equipment. Consequently consumer adoption of IPv6 is almost non-existent.
If consumers want remote access to network connected devices within their home or small office, Dynamic DNS is usually their only practical and cost-effective option.