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I have a Cisco C2950-24 Switch Out-Of-Box here. But my laptop doesn't have serial port nor I have the console hub.

Is there a way to setup the switch from this state without console access? I have a router that is feeding DHCP to the root port of the switch.

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The standard approach is to use a USB-to-serial adapter and a (Cisco) console cable to perform the initial configuration.

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Basically, the state of your current switch is unknown. Is it new from a factory, refurbished, used? Either way, there's no guarantee on how the switch was configured and what's on the unit. For example, I've had Cisco ASA firewalls come with DHCP enabled and mostly up-to-date, whereas many other devices came new with no network configuration and outdated software.

It may be worth the investment in a serial adapter at this point. The Tripp-Lite USA-19HS unit pictured above is quite popular and supports most operating systems.

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  • So for, Routers and ASAs, I don't need serial port. But for switches, I definitely need one, is what you are saying sir?
    – user192756
    Oct 5, 2013 at 4:31
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    No, you'll find a serial adaptor useful for all of those devices, unless you can be sure they all come with a clean factory config, and you know what their default IP configuration is, and you have a test network which you can set up to do the initial config. Really, the adaptor is a worthwhile investment; mine most definitely was.
    – MadHatter
    Oct 5, 2013 at 6:57
  • Agree with this except to say you may want to test a couple of different devices. We had users that needed a serial port for industrial systems and network gear and some did not work or worked poorly. Startech made some good ones and I am sure there are others. Check some reviews.
    – Dave M
    Oct 5, 2013 at 17:47
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If you are going to be working with network gear you will definitely want a serial port, it is the only guaranteed way to access a device console regardless of it's state or config. Take ewwhite's advice and get yourself an USB-to-serial adapter.

You mentioned that the switch is hooked up to a router, if they are physically near each other you can use the following nifty trick to access the console port in a pinch:

You need a cisco console cable with RJ45 connectors on both ends. You will use that to connect the CON port of the device you want to login to (device A) with the AUX port of a device we you have access to (device B, e.g. the router).

Login to device B and configure it’s AUX port with these settings:

# conf t
# line aux 0
(config-line)# modem InOut
(config-line)# transport preferred all
(config-line)# transport input all
(config-line)# transport output all
(config-line)# stopbits 1
(config-line)# end

Device B has to have a loopback address and it must be up. Now we have to find out which port we are going to have to telnet to. Do a show line from the enable mode, the output should look something like this:

Tty Typ Tx/Rx A Modem
0 CTY – –
* 97 AUX 9600/9600 – inout
* 98 VTY – -

Our line is number 97, telnet to the loopback address and port 2000+our line. If our loopback had the IP 192.168.100.200 the command would be telnet 192.168.100.200 2097 in this example.

I've used this trick a few times in the past when I had to remotely access the CON port of a device when the person on-site didn't have the right cable or laptop.

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You can use DHCP option 66 and 67 to configure the switch by pointing it to a TFTP server with a config file.

We use this feature for initial config of switches. Hold the mode button for 10 seconds and the switch will revert to factory defaults where the VLAN1-interface is a DHCP client.

When it comes to 2950's and DHCP client, I'm not sure if all ios version support it. It's a pretty old piece of kit. To find out what IOS version you are running, connect to the console and do a show version. No console cable say? Well, I guess you better go out and buy one. ;)

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