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:
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:
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 5.5 – # 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:
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.
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