Troubleshoot TCP connection issues from the ESX Service Console

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.