ah ok, see that is more helpful. but i have seen lots more threads, and to account for the people who are not posting and just browsing it seems like more of a possibility to me that its game related. my opinion. hopefully someone can fig this out id like to play the game
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This game is a PC and modem wrecker
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I had the same issue,
IF you guys are connected via ethernet cable to your router, then check out your CAT Type of your cable.
A (high tier) cat8.1 cable might try to use ressources your router or PC might not offer, this can finally lead to packetloss and/or disconnection and redial of your PC into your local network.
That’s what was told to me, when my problem was solved. Try out a Wlan-dongle before buying a new cable XD
300 million of my braincells just decided they don’t want to continue existing after reading that and a little drool went down my chin as a result, cheers for that! The bandwidth of the cable makes zero difference, the endpoints may saturate the connection, but having extra remaining does not… waiting for the braincells to repopulate… does not cause your entire Internet connection to drop.
Same issue as many others here and unique to Diablo 4 downloads/updates only. Never had any issues with other Blizzard games through battle.net client. Basically cripples my modem and affects my entire LAN’s internet connection. It’s crazy to me that there is a single official reply to this thread here when it’s clear there’s a somewhat widespread issue that’s pretty unique to Diablo 4 installs/updates.
Edit: I’m wondering if D4 update is acting like a torrent and distributing the patch amongst peers based on other posts I’m seeing about this issue.
Same for me. Diablo 4 crashes my internet and down. I can spend a whole day playing without anything happening, like suddenly it happens continuously. I’m using PC, and when I see that it goes wrong and something fails, I open the internet browser to see if the web pages work and youtube, and nothing works. But, right as soon as I close the game, EVERYTHING works again at the exact same moment I closed the game.
It all started in the middle ofJune more or less, by the date in the DDoS attack maybe. By 1.0.3. But I can’t say for sure when. I only know that the first weeks the game was perfect and never blocked the internet (even in the 3 betas it was all great).
obviously, I still didn’t dare to play Hardcore mode with this problem. and I want to play hardcore.
i can also add that i dont even have a router since im on a fiber optic cable provided diretcly into my house i have it straight into my computer. so it aint a router issue
make 0 sense it worked to this patch? we dont have trubbles whit other games? do we all have broken cables suddenly? i dont have a router fiber direclty into mycomputer…
it worked for me 
a network technican tried to explain it to me like that, sorry i damaged your neurons
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I have had the same issue every update after the launch. Acts like a DDOS and shuts down the whole network. Today I brainstormed with my brothers analyzing the router traffic and task manager. The only thing that “solved” the problem was to limit the bandwidth in battle.net launcher. (It did not work in the router settings as we tried that first). Sitting on a 100mbit fiberoptics and throttled first down to 2000kbps and then up to 4000kbps when realizing it worked. Gonna “finetune” it and find the limit another day. The download is of course slower but atleast everything works.
Oddly enough it SEEMS like it worked for me too. I tried 2 different cable (both cat 8) and always got my internet connection to crash. Now since the season started, I tried an older cable (cat 6) and so far - all good. Maybe I just got lucky so far, but considering I couldn’t stay in the game for more than 20 minutes before and now I’m grinding for hours … I don’t know. Might also be because of the new patch, but couldn’t find anything in Patch Notes that they changed something. If my internet connection should crash later on, I’ll update my post though 
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Works with every other game in the world except D4. I think the problem is Blizzard.
I just started having this issue when trying to download the latest patch. It starts to download then kills my entire internet connection, both TV and Internet Service (Bell 1.5g fiber). Only fix is to reboot the modem and things will come back online.
I had the same problem with my internet a lot of times when i downloaded the update/installation of diablo 4. But now it worked for me after i checked out the alternative high resoultion when install it. Just because it is for the players that have 4K monitors.
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Impressive that you have played every other game in the world to date. Not many people can claim that accolade.
I FOUND A FIX!
Add communication port com3 to windows 10 device manager and my ethernet hasn’t had problem since!
I believe all of you are using Browsers open while playing and searching and streaming, and watch streams ands alot of other stuffs… and Edge runs on Background when is closed unless you disable the run on background.
Test this:
Chrome: Security and Privacy, → Security → and disable → Use Secure DNS
Edge: Privacy, search, and services, → and disable → Use Secure DNS
Fixed
Nope, don’t assume things. All that is open is Battle.net & Steam. Steam is a constant and has no effect on the game. The only new thing is D4 with Battle.net.
If you are not assuming things, how are you counting on having help from anyone? Taking into account the number of people here with problems, would you want each person here to have a well-defined and fixed solution? The troubleshoot is anyway sometimes assuming something, in an attempt to discover the root of the problem, unless you are the smartest person in the world and know the future to know all the solutions to your problems.
People are really toxic. Did you at least test what I explained or did you simply post to pour out poison? You must play Rogue. Do you at least understand that Edge stays in the computer’s memory even if it is closed and has this new functionality that encrypts packets and bypasses your DNS connections from your ISP?.. and that can break your internet connection.
You are also assuming things.
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I have problems with Diablo 4 Xbox X Series, many times during the game disconnects and user game session is closed, it seems also xbox internet connection is closed for a few seconds.
I’m from Italy and use Telecom internet connection.
Can someone from support help me? Thanks