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Windows updates (win10) causes internet connection to become unstable

Recently, started since Windows 10 build 1607 (Anniversary update) and newer win10 editions like Creator and fall creators update, different sites/customers experience unstable internet connections to the internet when a single or multiple Win10 devices are performing windows updates from the internet. Internet responses are very slow, connections are dropping. When we manually disable Windows update on the client, internet is responsive again.

We already disabled the Windows Update Delivery Optimization "feature" in Windows 10 to no avail.

The strange thing is that a customer with multiple sites only experiences this behavior on sites where we have installed a Fortigate firewall. Some sites have a Draytek firewall with the same type of workstation and topology but don't experience this behavior when windows updates are occurring.



Happens on different customers/sites with different SMB Fortigate models 30, 40, 60  and different types C, D or E. 60D/E most used. Firmware is 5.2.x or 5.4.x.

The Fortinet firewall setup is plain and simple. Fortinet in NAT mode, just a fiber WAN connection (minimum of 30mbps) a single LAN connection and a simple all>all any > any policy from LAN to WAN. No UTM, No shapers.

Networkdevices behind firewall ranging from 5 to 40 win10 devices.

When we test the internetconnection with downloading or uploading large multigig files (by FTP for example) we don't experience internet unstability. It only happens with Windows update.

When a client is performing windows updates we can't see any indicators on the firewall device like high cpu, high mem, a lot of sessions, or sometimes even high bandwith. I use "get system performance status" on the devices and can't see anything unusual.


Does anyone have any idea why this is happening? Especially since win10 1607 and why a draytek for example does not experience this symptom.

When we use a traffic shaper as a workarround by limiting the bandwith to half of the available bandwith the connection seems to be stable, but this does not happen all the time.










one of my customer have this issue. once the win update start internet having issue. win10 using huge data on update from different server and also in fortigate it is not using the windows update application. it is using https.downloadaccelert  signature to detect this. 


i have blocked the update and suggest to use windows update service (windows wsus).





New Contributor III

We had a similar issue recently with certain machines having intermittent internet issues.  The web sessions would be closed immediately by the FG, but only for some users and at some times.  Other users on the same machine would have no problems.

We fixed it by upgrading our network card drivers on the machines in question.  It appeared to be related to the Realtek network cards in the affected machines. 




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