Moving the server’s physical location, and carrier-grade NATs.

So for the past several years, my server that is hosting this blog has been located at my father’s place. The only real reason for this was because his upload speed was 100Mbit/s and the one I have at home is 100Mbit down, but only “up to” 10Mbit/s upload. So even though it made it slower to access files on the server from my own home compared to if I just had it located there, it made more sense to have it at my father’s since it would mean that everyone that accesses it has the potential of downloading from it at 100Mbit/s.

But now, an era has passed, and my father is switching to a new ISP. In fact, he’s switching to the same ISP that I have at home, ComHem. Which means the upload speed at his place will also be “up to” 10Mbit/s. So after learning this I decided that it was time to move the server to my home instead, since now the upload speed will be the same regardless. And it also means that while I am at home I have gigabit access to the files which is nice.

So we move it to my place and I hook everything up. Everything just works with my network, as expected. I didn’t really change anything on the server itself so it should just work. Then I go to open the ports in my router, which it does allow me to do. But to my horror, I notice that the ports don’t appear to actually be opened to the outside world.

I google around quite a bit, and find info that suggests that ComHem utilizes a carrier-grade NAT (CGN) solution which basically means that I’m screwed. They have an internal NAT, where my public IP is assigned to many different customers, and obviously I can’t open the ports in ComHem’s routers. So I decide to give them a call to see if there’s anything I can do about the situation.

I call them up the next day, and get to speak to a lady on the broadband technical support team. I explain that I’ve been trying to open ports in my router but that I suspect my public IP might be shared with other customers. She tells me definitely that every router gets its own IP. So I ask, why then does the IP in my router differ from what I see on She is perplexed by this and can’t explain why. Then I see the hostname on whatsmyip, which includes the letters “cgn” at the start of it. I tell her this and says it must be that they’re using a carrier-grade NAT, and she says someone that knows a bit more about this specific issue will call me up. They never did.

I figure it might not be possible with ComHem with the way their networks are set up. I forget about it for a while since I was busy with other things, but this Monday I called them up again. I explained from the start that I had called before and figured out that I’m behind a CGN, and I ask if its possible to get my own public IP instead because otherwise I will never be able to open any ports. The lady I talked to this time was much more knowledgeable, and within minutes she had changed my router to be on its own public IP.

Not only that, but she saw that I was on a 100/10 connection and told me that they don’t offer that anymore. The lowest they have now is 150/10, which is the same price. So she also went ahead and upgraded me to that which was nice. To be fair, ComHem should’ve notified me about this at some point since now I’ve been paying for something I didn’t actually receive… but it was still nice of her to do.

My opinion of ComHem has been pretty bad since I got it. I don’t have a choice where I live, so I’m stuck with it. But it has definitely changed for the better after that last call to their support. I’m definitely more positively inclined towards them after this Monday. So thank you, lady on the broadband tech support, you really made my day. It’s thanks to you that it’s possible to read this blog entry!

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