Cannot connect to mongos Following the MongoDB Sharding Documentation, I start a mongos using a configuration file with the specifics of my config server. 

It seems rather straightforward, yet I am running into an issue. I start mongos on one machine (lets say its ip address is "some_ip"):

$ sudo mongos --config /etc/some_config.conf


And I try connecting to its shell from another machine, but I get connection refused error.

$ mongos some_ip:xxxxx


Here's part of my some_config.conf file:

    net:
      port: xxxxx
      bindIp: 0.0.0.0

   sharding:
      configDB: &lt;configReplSet&gt;/&lt;ip_of_config&gt;:27019


I'm using 0.0.0.0 for testing purposes. I made sure that the ip_addr and port I'm connecting to matches the ip of the host for the mongos and the port I specified in the net.port param. I also opened up this port in my firewall for ingress/ egress connections.

Did I miss anything ? (NOTE: ** I edited post for further clarification)

UPDATE

(note: i replaced the actual ip addr with "ip_of_config")
This is what my log file for my mongos says when I start mongos.

2018-05-02T05:57:48.533+0000 W NETWORK  [monitoring keys for HMAC] Failed to 
connect to &lt;ip_of_config&gt;:27019, in(checking socket for error after poll), reason: 
Connection refused
2018-05-02T05:57:48.533+0000 W NETWORK  [monitoring keys for HMAC] Unable to 
reach primary for set crs0


Now my config server is up and running fine, but its log file shows that it accepts multiple connections from my mongos server, but these connections close almost immediately. Also there are a few warning logs:

W SHARDING [Balancer] Balancer settings could not be loaded and will be 
retried in 10 seconds :: caused by :: ReadConcernMajorityNotAvailableYet: 
Failed to refresh the balancer settings due to 
ReadConcernMajorityNotAvailableYet: Read concern majority reads are currently 
not possible.

W SHARDING [shard registry reload] cant reload ShardRegistry  :: caused by :: 
CallbackCanceled: Callback canceled
mongos for “MongoDB Shard,” is a routing service for MongoDB shard configurations that processes queries from the application layer, and determines the location of this data in the sharded cluster, in order to complete these operations. From the perspective of the application, a mongos instance behaves identically to any other MongoDB instance.

As you have mention here mongos.conf file 

 net:
      port: xxxxx
      bindIp: 0.0.0.0

   sharding:
      configDB: &lt;configReplSet&gt;/&lt;ip_of_config&gt;:27019


As here i would like to say that here as you are bindIp in mongos.conf file with 0.0.0.0 but in sharding section , you are using  with port number 27019 of any replica set. 

Note : As here I am not able to see any logpath destion in your mongos.conf file. 

As per MongoDB BOL documentation here Starting in MongoDB 3.6, mongos bind to localhost (127.0.0.1) by default.

Did you try with this configuration of your mongos.conf file.

sharding:
  configDB: replicasetname/ipaddress:27019 -- external ip of replica set of any node which port is 27019, as you mention in your code. which must be participate the replication. 
 net:
  bindIp: localhost,ipaddress -- external ip address, if you are using  
  port: xxxxx --port number of mongos, it should be different from replica set node port number
systemLog:
  destination: file
  path: -- log destination of mongos file
  logAppend: true
processManagement:
  fork: true             -- if you are using the fork