Prior to Receiver 4.0, Administrators were unable to connect through certain Proxies that restrict connections from certain IP address, requiring the administrators to configure the client side ProxyUseFQDN registry setting.

Use the minimum required Citrix Receiver 4.x for Windows or latest version available which automatically connects by FQDN (without the need for client side changes) through a Proxy Server if a Proxy server is detected for the ICA connection, otherwise it will resolve the FQDN to IP address and then connect by IP address to the target device.

Problem Cause

Prior to Receiver 4.0, by default the Receiver client would attempt to resolve the FQDN of the target device (example: SG/AG Server, XA server) to IP address and then attempt to connect to the IP Address through a configured Proxy Server.

The issue with this approach is that some Proxy Servers might block connections that are made by IP address through the Proxy Server.

In some environments, the DNS server might not be configured to return the correct IP address for an external device. Such an environment depends on the Proxy Server to resolve the FQDN of the target device to an IP.

The workaround in the past was to set client side setting ProxyUseFQDN=on OR off in the Receiver for Windows client registry so that the Receiver for Windows client would CONNECT by FQDN to the Proxy Server and depend on the Proxy Server to resolve the FQDN to IP.

Use of this workaround at times for various reasons in the past would result in issues in environments that might not have a Proxy server or that might have a non-standard Proxy type setup.

Citrix Documentation - ICA Settings Reference​