What Carrier-Grade NAT Is and How Starlink Uses It
Carrier-grade NAT (CGNAT) is a network technique where an internet provider shares a single public IPv4 address among many customers by translating thousands of private connections, which conserves scarce IPv4 space but adds limits on how many simultaneous sessions each user can keep open. Starlink Residential and Roam plans rely on CGNAT for their default IPv4 configuration, placing subscribers behind shared addresses instead of giving each terminal its own public IPv4. According to Starlink’s support documentation, these plans have “a limit of 1,200 concurrent sessions” over TCP or UDP, and “when the 1,200-session limit is reached, new sessions automatically cause the oldest sessions to be dropped.” CGNAT is common across modern ISPs and exists mainly because IPv4 addresses are in short supply, even as Starlink and others move large parts of their traffic to native IPv6.
Why CGNAT Creates Internet Session Limits on Starlink
Under CGNAT, every outbound TCP or UDP connection becomes a “session” that must be tracked by the provider’s translation hardware. To prevent a few heavy users from consuming disproportionate resources, the CGNAT standard encourages ISPs to cap active sessions, which is where the Starlink CGNAT limitation of 1,200 concurrent sessions comes from. Each device and app on your network adds to that count. Browsers open multiple connections per tab, streaming services may keep several streams alive, and background sync tools maintain persistent links. Starlink notes that when the limit is hit, new connections can silently drop older ones. Most households will not touch 1,200 IPv4 sessions because a large share of traffic now goes over IPv6, but a busy home lab, dozens of smart devices, or a misconfigured peer-to-peer client can push your connection over the edge.
How CGNAT Feels for Gamers, Power Users, and Home Labs
The Starlink CGNAT limitation tends to show up as strange, intermittent Starlink connectivity issues rather than a complete outage. Online games may randomly disconnect, voice chat can go silent mid-sentence, and long-running VPN tunnels may drop without warning. Starlink’s documentation highlights “applications that use many simultaneous connections,” naming VoIP calls, video conferencing, online gaming, and VPNs as examples. Power users are more at risk because one busy machine can spawn hundreds of sessions—think game launchers, cloud backups, developer tools, or containers in a home lab. Add several streaming devices, smart home gear, and work laptops, and the total count can creep close to the 1,200-session ceiling. When that happens, the CGNAT system starts expiring older sessions to make room for new ones, which shows up as unexplained logouts, stalled downloads, or recurring “connection lost” errors.
Why Starlink Still Needs CGNAT in an IPv6 World
CGNAT exists mainly because IPv4 addresses are scarce, and Starlink is no exception. Instead of assigning a unique IPv4 address to every terminal, Starlink uses ranges such as 100.64.0.0/10 for Residential and Roam plans, with CGNAT mapping many private users to fewer public addresses. At the same time, the company pushes hard toward IPv6, where address space is effectively abundant and one-to-one assignment is easy. Networking consultant Daryll Swer notes that “about 80% of the internet traffic for an average Starlink customer could route through the newer IPv6 protocol” thanks to major content delivery networks being natively IPv6-enabled. But IPv6 is not backward compatible with IPv4, and many important services, including high-profile developer platforms and legacy sites, still lack IPv6. Those IPv4-only destinations keep users tied to CGNAT and its internet session limits.
Practical Workarounds to Reduce Starlink CGNAT Pain
You cannot remove the Starlink CGNAT limitation on Residential or Roam, but you can reduce how often you hit it. Start by trimming unnecessary connections: close unused browser tabs, pause aggressive peer-to-peer or sync tools, and schedule large downloads or backups for off-hours. On your router, enable IPv6 so more traffic bypasses IPv4 CGNAT, and disable overly chatty features like constant device cloud polling where possible. Power users can segment noisy devices onto a separate VLAN or SSID, making them easier to monitor and tame. For gaming and VPNs, limit simultaneous sessions from launchers or clients that keep many servers open. If you run a home lab, cap container counts and connection pools. These tweaks do not raise the 1,200-session ceiling, but they help you stay below it, making your Starlink connection feel far more stable.
