How to disable ESX 6.5 virtual serial port telnet server to echo FF FD 25?

[totoroliu]

After enable Virtual Serial Port over network using telnet protocol on ESX 6.5,

when using Python telnetlib library to do telnet connection,

ESX telnet server would echo back '\xff\xfd%' after the first write.

After digging into RFC 854 - Telnet Protocol Specification ,

'\xff\xfd%' is IAC DO command.

Is there any easy way I can config Virtual Serial Port telnet server from ESX server to disable the echo?

Here's a sample Python script to try:

import time
import telnetlib
HOST = "172.18.125.43"
PORT = "7004"
tn = telnetlib.Telnet(HOST, PORT)
tn.set_debuglevel(10)
for i in range(5):
    tn.write("\n")
    time.sleep(1)
    tn.read_very_eager()
tn.close()

Example output:

Telnet(172.18.125.43,7004): send '\n'

Telnet(172.18.125.43,7004): recv '\xff\xfd%\r\n\r\nLogin: '

Telnet(172.18.125.43,7004): IAC DO 37

Telnet(172.18.125.43,7004): send '\n'

Telnet(172.18.125.43,7004): recv '%\r\nPassword: '

Telnet(172.18.125.43,7004): send '\n'

Telnet(172.18.125.43,7004): recv '\r\n'

Telnet(172.18.125.43,7004): send '\n'

Telnet(172.18.125.43,7004): recv '\r\n'

Telnet(172.18.125.43,7004): send '\n'

Telnet(172.18.125.43,7004): recv '\r\n'

[mhampto]

To confirm what is being done, you are configuring a Serial port to a virtual machine or to the ESXi host?

[totoroliu]

I'm configuring a Virtual Serial Port to a virtual machine.

[totoroliu]

It looks like there's noe way to turn off the echo of control-stream "FF FD 25".

Eventually, we add extra handling to expect the control-stream.