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I guess thats the MTU issue @Sacha Thomet describes here: https://blog.sachathomet.ch/de/2020/06/04/citrix-cvad-und-mtu-discovery/

I have also observed the same issue with Service Provider specific, I suggested customer to disable just IPv6 for client machine and reboot then try

Here the english one: https://blog.sachathomet.ch/2020/06/04/citrix-cvad-und-mtu-discovery/

MTU Discovery seems to be solution. However it seems to be something wrong with configuration on Vodafone as it’s the only one internet provider with such issue for us. Am I right ?

No I have the problem with several small German isp. Because the have only ipv6 and that ipv6 to ipv4 redirection shit kills the mtu. The whole citrix udp connection are allergic to it.

@Rody Kossen I vaguely recall you reporting something like this as well?

same problem with other small isps in Italy.

I always write the same answer: I‘m a MSP in Germany, we have to disable UDP/EDT in every single CVAD deployment. It just never works.

@Kees Baggerman indeed. I've worked with a Dutch ISP to solve this issue. Conclusion: DS-LITE ( IPv4 over a v6 tunnel) had a firmware issue that breaks MTU discovery. This is something the ISP should fix ( which the Dutch ISP did) and it can cause issues with other udp based apps as well. You can check the MTU size by running ctxsession -v, if you see issues and MTU is around 1500 then it's probably the same issue. I'm happy to help out if somebody has a contact at the ISP. As a work around either use TCP for these users or disable EDT MTU Discovery and set a fixed size in the default.ica