While the ping command confirms connectivity, it does not necessarily mean that all TCP ports on the remote host can be reached. It is possible for a network firewall to allow or block access to certain ports on a host.

 

To check if specific TCP ports are running on the remote host, you can use the telnet command to confirm if a port is online.

# telnet destination-ip destination-port

When trying to establish a telnet connection to TCP port 80, you see an output similar to:

 

# telnet 192.168.1.11 80Trying 192.168.1.11…

Connected to 192.168.1.11.

Escape character is ‘^]’.

In this sample output, you can see that you are connected to port 80 (http) on the server with IP address 192.168.1.11.

 

If you choose a port number for a service that is not running on the host, you see an output similar to:

 

# telnet 192.168.48.1.11 

Trying 192.168.1.11…

telnet: Unable to connect to remote host: Connection timed out

In this case, you can see that there is no response when you attempt to connect to port 81 on the server 192.168.48.133.

Note: Telnet is an application that operates using the TCP protocol. UDP connectivity can not be tested using Telnet.

 

Viewing active TCP/UDP connections with netstat and esxcli network

When troubleshooting network connectivity issues, it may be helpful to see all the active incoming and outgoing TCP/UDP connections on an ESX/ESXi host. ESX hosts can use the netstat command and ESXi 4.1 and later hosts can use esxcli network to show the list of TCP/UDP connections. The commands are: 

ESX 3.5/4.x – # netstat -tnp

ESXi 4.1 – # esxcli network connection list

ESXi 5.0 – # esxcli network ip connection list

 

ESXi 5.1 – # esxcli network ip connection list 

ESXi 5.5 – # esxcli network ip connection list

ESXi 6.0 – # esxcli network ip connection list

ESXi 6.5 – # esxcli network ip connection list

Sample output from an ESXi 4.1 host:

 

# esxcli network connection list 

Proto  Recv-Q  Send-Q  Local Address       Foreign Address     State        World ID

tcp    0       52      192.168.1.11:22   192.168.25.1:55169  ESTABLISHED  0

tcp    0       0       127.0.0.1:62024     127.0.0.1:5988      TIME_WAIT    0

tcp    0       0       127.0.0.1:57867     127.0.0.1:5988      TIME_WAIT    0

tcp    0       0       127.0.0.1:62196     127.0.0.1:5988      TIME_WAIT    0

tcp    0       0       127.0.0.1:8307      127.0.0.1:52943     ESTABLISHED  5790

tcp    0       0       127.0.0.1:52943     127.0.0.1:8307      ESTABLISHED  5790

tcp    0       0       127.0.0.1:80        127.0.0.1:55629     ESTABLISHED  5785

tcp    0       0       127.0.0.1:55629     127.0.0.1:80        ESTABLISHED  6613

tcp    0       0       127.0.0.1:8307      127.0.0.1:56319     ESTABLISHED  5785

tcp    0       0       127.0.0.1:56319     127.0.0.1:8307      ESTABLISHED  5785

tcp    0       0       127.0.0.1:80        127.0.0.1:62782     ESTABLISHED  5166

tcp    0       0       127.0.0.1:62782     127.0.0.1:80        ESTABLISHED  6613

tcp    0       0       127.0.0.1:5988      127.0.0.1:53808     FIN_WAIT_2   0

tcp    0       0       127.0.0.1:53808     127.0.0.1:5988      CLOSE_WAIT   5166

tcp    0       0       127.0.0.1:8307      127.0.0.1:56963     CLOSE_WAIT   5788

tcp    0       0       127.0.0.1:56963     127.0.0.1:8307      FIN_WAIT_2   5785

tcp    0       0       127.0.0.1:8307      0.0.0.0:0           LISTEN       5031

tcp    0       0       127.0.0.1:8309      0.0.0.0:0           LISTEN       5031

tcp    0       0       127.0.0.1:5988      0.0.0.0:0           LISTEN       0

tcp    0       0       0.0.0.0:5989        0.0.0.0:0           LISTEN       0

tcp    0       0       0.0.0.0:80          0.0.0.0:0           LISTEN       5031

tcp    0       0       0.0.0.0:443         0.0.0.0:0           LISTEN       5031

tcp    0       0       127.0.0.1:12001     0.0.0.0:0           LISTEN       5031

tcp    0       0       127.0.0.1:8889      0.0.0.0:0           LISTEN       5331

tcp    0       0       192.168.1.11:427  0.0.0.0:0           LISTEN       0

tcp    0       0       127.0.0.1:427       0.0.0.0:0           LISTEN       0

tcp    0       0       0.0.0.0:22          0.0.0.0:0           LISTEN       0

tcp    0       0       0.0.0.0:902         0.0.0.0:0           LISTEN       0

tcp    0       0       0.0.0.0:8000        0.0.0.0:0           LISTEN       4801

tcp    0       0       0.0.0.0:8100        0.0.0.0:0           LISTEN       4795

udp    0       0       192.168.1.11:427  0.0.0.0:0                        0

udp    0       0       0.0.0.0:427         0.0.0.0:0                        0

udp    0       0       192.168.1.11:68   0.0.0.0:0                        4693

udp    0       0       0.0.0.0:8200        0.0.0.0:0                        4795

udp    0       0       0.0.0.0:8301        0.0.0.0:0                        4686

udp    0       0       0.0.0.0:8302        0.0.0.0:0                        4686

To retrieve errors and statistics for a network adapter, run this command:

# esxcli network nic stats get -n <vmnicX>

Where <vmnicX> is the name of a NIC in your ESXi host.