iPhone Update Verification Failed from home network

by Daywalker   Last Updated September 03, 2019 22:12 PM

I have a problem when I try to install iOS or whatOS Updates from my home network.
It always stops after the verification process, and tells me that the verification failed, and I should check my internet connection. So I did that

My Firewall is a pfsense box with two internet connections.
ISP_1 is DSL connected
IPS_2 is LTE connected

When I disable ISP_1 OR make the update over my local Internet connection on my phone, the update works.

So It seems to be an issue with ISP_1, but i'm out of ideas what might be the problem?
Updating an iPhone is possible without WLAN, but updating the apple watch is impossible.

May be a network or Firewall guy can help

Additional Information: When Updating over ISP_1 line I see a lot of Retransmits FROM my phone to an Apple owned IP (17.x.x.x/8)
This NOT the case when I do the update over ISP_2!

All those connections are IPv4 only, and all outgoing traffic is allowed without any modifications.

For now I helped myself with a simple rule which sends out all Traffic directed to over ISP_2. But that's only a workaround, not a solution...

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