Connection data to etcd outside of istio get modified

I’m using istio 1.3.6 with kubernetes, and I use etcdctl in pod to connect to an external ip address to get etcd data. The external etcd use the same port number as the etcd deployment alongside with istio which is 2379.
It is supposed that because the ip is out side the cluster , the data can pass istio-proxy and be transfered directly to the external etcd node. but it seems that, the data is modified.
If i deploy a ServiceEntry for the external etcd node , then everything will be ok.