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What Is CGNAT and How Does It Affect Your Broadband?
CGNAT means Carrier-Grade Network Address Translation. It lets an internet provider share public IPv4 addresses between customers. The practical distinction is most important when you want a connection from the internet to reach a device or service inside your home.
How CGNAT differs from your router’s NAT
A home router commonly translates traffic between private addresses on the local network and its internet-facing address. CGNAT adds translation within the provider’s network. Configuring your own router does not give you control of that additional layer.
Why inbound connections and port forwarding matter
If you host a server, VPN endpoint or another service that needs unsolicited inbound IPv4 connections, CGNAT can prevent conventional router port forwarding from making it reachable. The solution depends on the provider and application: a public address, supported IPv6 or an appropriate relay or tunnel may be options.
That does not mean ordinary browsing, streaming or every VPN stops working. Many applications initiate their connections outwards or use traversal and relay mechanisms. Gaming behaviour also depends on the particular game and network arrangement; lag alone does not establish that CGNAT is the cause.
Is a public address the same as a static address?
No. A public address is routable on the public internet. A static address is intended to remain assigned rather than changing dynamically. Ask separately whether the service uses CGNAT, provides a public IPv4 address and offers a static-address option.
What about IPv6?
IPv6 uses a much larger address space and can provide a separate path for compatible services. Both ends need the relevant support, and firewall rules still matter. IPv6 availability does not by itself tell you whether a provider uses CGNAT for IPv4.
Questions to ask your broadband provider
Explain the application you need to use. Ask whether inbound access is supported, which IP address options are available and whether any extra configuration or charge applies. Keep router and device security settings appropriate for anything exposed to the internet.
Exascale’s current CityFibre offering is advertised without CGNAT. Check the CityFibre service page for current package details and ask Exascale about static IPv4 and IPv6 options for your service rather than assuming every address feature is automatically enabled.
Related technical guides
For router configuration, see bringing your own router to Exascale. For connection protocols rather than address sharing, read PPPoE vs DHCP. The IETF’s RFC 6598 describes the shared address space reserved for carrier-grade NAT.
