If you need to troubleshoot TCP connection issues from your ESX host. You will notice that Telnet isn’t available on your ESX host. But VMware posted a workaround in KB1010747. The reason why VMware did not include the Telnet package is simple:

The TELNET package does not ship with the ESX service console. While the TELNET daemon is clearly a security risk, the TELNET client may be a useful tool in diagnosing TCP session connectivity between the ESX Service Console and TCP ports on a foreign host.

The workaround is a Python script. You can copy the following script to your ESX host and place it in /tmp directory.

#!/usr/bin/python
# TCP connection "tester" -
# provide the hostname/IP address followed by port number (if no port
# is specified, 23 is assumed ;)
# program will connect to the port and read till either it receives a
# newline or 5 seconds expire
# be sure to chmod 755
import sys
import telnetlib
import socket

PORT = ""
argc = len(sys.argv)

if argc == 3 :
    PORT = sys.argv[2]
elif argc < 2 or argc > 3:
    print "usage %s host <port> \n" % sys.argv[0]
    sys.exit()

HOST = sys.argv[1]

try:
    tn = telnetlib.Telnet(HOST,PORT)
except socket.error, (errno, strerror):
    print " SockerError( %s ) %s\n" %  (errno, strerror)
    sys.exit()

print tn.read_until("\n ",5)
print "connection succeeded\n"
tn.close()
sys.exit()

If you want to test if a particular TCP port is reachable from your ESX host. You can use the script like this:

[root@esx01 ~]# ./testtcp vc01.ict-freak.loc 443

connection succeeded

[root@esx01 ~]#

In case the TCP port is not reachable from your ESX host. The script will just hang on your command and will eventually time out:

[root@esx01 ~]# ./testtcp vc01.ict-freak.loc 443
SockerError( 110 ) Connection timed out

You can also cancel the script by pressing CTRL + C

I didn’t test the script from ESXi. If you did, please leave a comment.

Source:

KB1010747