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Media server behind CGNAT: why remote streaming fails

Your media server works fine at home, but your phone can't reach it on mobile data or at a friend's place. If your ISP uses CGNAT, that's expected: the connection from outside never reaches your house.

Why CGNAT gets in the way

To watch from outside your home, your phone or TV has to open a connection into your network, to the server's port. Normally you forward that port on your router. Behind CGNAT, your router doesn't hold a public IPv4 address, so the port would also have to be opened on the ISP's NAT, which only the ISP controls (RFC 6269, section 5.2.1).

What works and what doesn't

Streaming inside your home network: CGNAT doesn't touch local traffic.
Your server downloading things (metadata, updates): that's outgoing, so it works.
Watching from outside over IPv4: blocked, unless your ISP gives you a public IPv4.
Watching from outside over IPv6: can work if your ISP gives you IPv6, the viewing device's network has IPv6 too, and your router's IPv6 firewall allows the port.

Check whether you're behind CGNAT

Compare your router's WAN address with your public IP using the CGNAT checker or the step-by-step guide. A WAN address between 100.64.0.0 and 100.127.255.255 is the CGNAT range (100.64.0.0/10 explained). If the two addresses match, CGNAT isn't your problem; check the port forward and any inbound port blocks your ISP lists.

What to ask your ISP

"Can you move my line off CGNAT and give me my own public IPv4?" Some ISPs do this for free on request; others only with a paid static IP.
"Do you sell a static IP on residential plans, and what does it cost?" Some ISPs only sell it on business plans.
"Is IPv6 available on my line, and is it turned on?" IPv6 doesn't go through the CGNAT, but the other side needs IPv6 too.
"What upload speed does my plan really have?" Remote streams leave your house over your upload, so a slow upload limits how many people can watch and at what quality. The ISP finder shows which providers offer symmetrical upload.

Which ISPs make this easier

Of the 41 ISPs we track, 12 give home customers a public IPv4 by default, 3 offer a free CGNAT opt-out and 8 sell a static IP on home plans, per our sources. See ISPs without CGNAT, ISPs that use CGNAT, or filter the ISPs without CGNAT that offer symmetrical upload in your state. Each ISP page also quotes what the terms say about running servers at home.

FAQ

Why can't I reach my media server from outside my home?

If your ISP uses CGNAT, your router doesn't have its own public IPv4 address, so incoming connections from the internet stop at the ISP's NAT and never reach your server. Port forwarding on your router can't fix that by itself.

Does CGNAT affect streaming inside my house?

No. Devices on your home network talk to the server directly, so local streaming works the same with or without CGNAT.

What should I ask my ISP?

Ask whether it can move your line off CGNAT to a public IPv4, whether it sells a static IP on home plans, and whether IPv6 is available and turned on. Also check your upload speed, since remote streams use it.

Is running a media server allowed on a home plan?

It depends on the ISP. Some residential terms restrict running servers. Each ISP page on this site quotes what the terms say.

This site sticks to ISP facts. It doesn't review or recommend third-party products or services.