Created attachment 35465 [details] tcpdump showcasing the extra AAAA dns query Azure's Application Gateway forwards the useragent ip via the X-Forwarded-For header as documented [1] and adds the port to it. Trouble is that remoteip picks up and does a AAAA dns query resulting obviously in a negative response. This should not happen - stripping of the port there is no extra dns query. [1] https://docs.microsoft.com/en-us/azure/application-gateway/application-gateway-faq I've attached a tcpdump that showcase the error.