Starlink is a popular way to get fast internet connectivity pretty much anywhere in the world. There are some limitations however, which we'll explore later in this article. The main topic for discussion is what CGNAT is and how to relates to Starlink. To understand what CGNAT is, we need to look at how ISPs get connectivity to you in the first place.

ISPs use the following technology to get you online:

• Static public IP addresses
• Dynamic public IP addresses
• Shared public IP address
• CGNAT (Carrier-grade NAT)

Dynamic Public IP address

Most ISPs use either static or dynamic public IP addresses. Using dynamic public IP addresses means that the WAN IP address you get from your ISP will be a public IP address, so applications such as Xbox Live that require a certain level of NAT would still work. Because IPv4 IP addresses are scarce, when a user has their router or equipment switched off, that IPv4 address can go back in the pool to be repurposed if needed.

Static Public IP address

Having a static public IP address gives you the same benefits as a dynamic one, with proper support for Xbox Live and making sure that NAT levels are what they should be. However, as the name suggests it is static, meaning you will always have that same IP address, even if your equipment gets turned off. This does provide some added benefits such as port forward, IP whitelisting and hosting. Most ISPs will even offer multiple IP addresses, which can be used for various applications such as email servers and web servers, if needed.

Static IP addresses usually command a premium on top of your monthly charge, due to IPv4 addresses being scarce.

CGNAT

CGNAT (Carrier-grade NAT) is used by some smaller ISPs that find it difficult to get a huge allocation of IPv4 addresses. It helps prevent IP exhaustion, without the need to switch over to IPv6. There are a number of downsides in using CGNAT, such as issues with NAT, due to the CGNAT added another layer. Port forwarding is also out of the question too, but some services such as VPNs and Xbox Live will be able to work, in some cases.

Some VPN services can be used to get around the CGNAT restrictions on Port Forwarding, such as PureVPN.

Starlink and CGNAT

Starlink uses CGNAT to avoid the need for 1,000s of IPv4 addresses and due to how some users are using Starlink, this would be quite a huge issue. Starlink could have used Dynamic Public IP address, but instead it opted to use CGNAT. For the most part, it isn't a huge issue and users have managed to use workarounds to get port forwarding working.

So what are the main issues with CGNAT?

• Shared public IP address with multiple users
• Reduced flexibility
• No port forwarding support
• Extra layer of NAT, breaks some services

Late last year, some users on Reddit noticed that they were starting to get a routed IPv4 IP address too, but not everyone has since seen this. This could be a one off or for testing purposes.

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