elasticsearch nest SniffingConnectionPool not working - elasticsearch-net

Question

I'm using Nest.ElasticClient to connect to Elasticsearch cluster. The cluster is located in Azure VM with just one node.
the cluster is accessible outside the vm by url : http://xxxx.cloudapp.net:9200 and also accessible by ElasticClient if not using SniffingConnectionPool. But not accessible by ElasticClient if using SniffingConnectionPool.
Here is the network config
network.host: [_local_, _site_]
Below is the source code I'm using to get client and check index exists.
var pool = new SniffingConnectionPool(urls.Select(url => new Uri(url)));
ConnectionSettings config = new ConnectionSettings(pool) ;
client = new Nest.ElasticClient(config);
IExistsResponse indexExistsResponse = client.IndexExists(indexName);
The debug info message when I try to use the client to check whether a Index exists, the hostnanme and ip address is modified:
Invalid NEST response built from a unsuccessful low level call on HEAD: /globalleads
# Audit trail of this API call:
- SniffOnStartup: Took: 00:00:00.9846171
- SniffSuccess: Node: http://xxxx.cloudapp.net:9200/ Took: 00:00:00.9595496
- PingFailure: Node: http://10.85.xxx.xx:9200/ Exception: PipelineException Took: 00:00:21.4154660
- SniffOnFail: Took: 00:00:21.1967809
- SniffFailure: Node: http://10.85.xxx.xx:9200/ Exception: PipelineException Took: 00:00:21.1787333
# OriginalException: Elasticsearch.Net.ElasticsearchClientException: One or more errors occurred. ---> System.AggregateException: One or more errors occurred. ---> Elasticsearch.Net.PipelineException: Failed sniffing cluster state. ---> System.AggregateException: One or more errors occurred. ---> Elasticsearch.Net.PipelineException: An error occurred trying to establish a connection with the specified node.
at Elasticsearch.Net.RequestPipeline.Sniff() in D:\dev\git\elasticsearch-net-2.x\src\Elasticsearch.Net\Transport\Pipeline\RequestPipeline.cs:line 326
--- End of inner exception stack trace ---
--- End of inner exception stack trace ---
at Elasticsearch.Net.RequestPipeline.Sniff() in D:\dev\git\elasticsearch-net-2.x\src\Elasticsearch.Net\Transport\Pipeline\RequestPipeline.cs:line 341
at Elasticsearch.Net.RequestPipeline.SniffOnConnectionFailure() in D:\dev\git\elasticsearch-net-2.x\src\Elasticsearch.Net\Transport\Pipeline\RequestPipeline.cs:line 301
at Elasticsearch.Net.Transport`1.Ping(IRequestPipeline pipeline, Node node) in D:\dev\git\elasticsearch-net-2.x\src\Elasticsearch.Net\Transport\Transport.cs:line 179
at Elasticsearch.Net.Transport`1.Request[TReturn](HttpMethod method, String path, PostData`1 data, IRequestParameters requestParameters) in D:\dev\git\elasticsearch-net-2.x\src\Elasticsearch.Net\Transport\Transport.cs:line 68
--- End of inner exception stack trace ---
--- End of inner exception stack trace ---
# Audit exception in step 2 PingFailure:
Elasticsearch.Net.PipelineException: An error occurred trying to establish a connection with the specified node.
at Elasticsearch.Net.RequestPipeline.Ping(Node node) in D:\dev\git\elasticsearch-net-2.x\src\Elasticsearch.Net\Transport\Pipeline\RequestPipeline.cs:line 248
# Audit exception in step 4 SniffFailure:
Elasticsearch.Net.PipelineException: An error occurred trying to establish a connection with the specified node.
at Elasticsearch.Net.RequestPipeline.Sniff() in D:\dev\git\elasticsearch-net-2.x\src\Elasticsearch.Net\Transport\Pipeline\RequestPipeline.cs:line 326
# Request:
<Request stream not captured or already read to completion by serializer. Set DisableDirectStreaming() on ConnectionSettings to force it to be set on the response.>
# Response:
<Response stream not captured or already read to completion by serializer. Set DisableDirectStreaming() on ConnectionSettings to force it to be set on the response.>