Gaining access to an unconfigured Cisco 3750 Switch without Console, Telnet and SSH Access

Huh!! What happens when you need to configure a Cisco 3750 immediately for production network but unfortunately you don’t have console, telnet, or SSH access? I know it’s damn scary and if it happens at 02:00 hours then you have no one to help you.

Problem:

Recently during an installation, I faced the exact same situation where I was presented with a Cisco 3750 switch but no methods of accessing it. Forget about SSH and Telnet as no Management VLAN was configured in it [It was totally an unconfigured one].

You might be thinking of Console access. Right? Damn it was not accessible too. Let me tell you the problems in brief.

  • Only 1 PC had a Serial port and had only Ethernet to Console cable. No USB to Serial Converter were there.
  • Console only displayed debug messages but keystrokes were were accepted.
  • All the settings on my hyper terminal were correct and it was as per Cisco’s recommendation.
  • Tried variations of Flow Control, baud rate etc but none helped.
  • Tried atleast 4 different applications for console access including putty, hyper terminal, secure crt, tera term. Results were all same.
  • Tried 4 brand new console cables.

After spending about 1 hour trying to figure out getting access to console, I was pretty sure something was messed up in the console access and I didnot have the USB converter to check it alternatively.

Tried Recovery mode too but as keystrokes were not accepted no way of typing anything into recovery mode.

Solution:

  • Let the switch boot itself and you can see all the logging messages in the console screen.
  • After the switch is ready, press and hold the Mode button located in the front left side of the switch.
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  • Release the button as all the light starts glowing.
  • Now in your console screen you will see a message – “Express Setup Mode”.
  • Connect an ethernet cable and plug it into the switch (any port). Make sure your NIC is set to “Obtain IP Address Automatically”.
  • You will notice that your PC will get an IP address in the 10.X.X.X series and DHCP allocation message will also be displayed on the console screen.
  • Now, find the default gateway assigned to you but the Switch’s DHCP Server.
  • Login via telnet to that server. No password will be asked.
  • Issue the following command – setup
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  • You will be presented with a “System configuration Dialog”. Type Yes to enter the system.
  • Give the following details one by one:
    #Hostname
    #Enable Secret
    #Password
    #Management Interface (I selected Management VLAN 1)
    #Assign IP & Subnet Mask (Assign some Class C or Class B IP. Don’t Give Class A IP now as this is already assigned by DHCP Server, I gave 192.168.254.1/24)
  • After you have given the above mentioned details, you will be presented with a configuration script automatically created based on your given details.
  • Double check all configurations. Then if your are sure then press 2.
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  • It will save the configs.
  • Your remote connection will be terminated immediately as Express setup will now exit followed by switch reboot but no worries.
  • Next Set your PC’s IP to the same network as set in Management VLAN 1. ( I set it to 192.168.254.254/24).
  • Telnet into your switch’s IP (192.168.254.1). Enter the passwords and voila you are good to go.

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  • Dwayne Wayne

    Wait a minute !!! Your troubleshooting says you couldn’t see anything on the Console.. but your solution says to boot and wait message in Console. Which is it? Did you see data appear in console or not?

    Your words: You might be thinking of Console access. Right? Damn it was not accessible too.

    Also your solution: Let the switch boot itself and you can see all the logging messages in the console screen.

    So how can you see data form the switch booting if you cant get the console to work?