I'm not sure about your problem but it really seems like a network config in DCOS.
Let's start from the beginning, try to figure out the address and port of Kibana by trying to access it from a server inside DCOS cluster and using the command line with curl -XGET 10.128.0.6:5601/api/status.
If you get a connection refused error you are simply not pointing to the right address:port and you must first ensure of where it is. If address:port is correctly set, you'll get either a Kibana server is not ready yet or a long JSON response with data.