External Service Entry to support ldap,netconf

I try to use serviceEntry with TCP,but it doesn’t work,I got te log like this:
[Envoy (Epoch 0)] [2020-06-12 06:46:32.240][15][trace][connection] [external/envoy/source/common/network/raw_buffer_socket.cc:38] [C1] read error: Resource temporarily unavailable

Is there any other logs to need to debug this problem?