Basics of cisco switch administration

1. Basics of Cisco Switch Administration
Basics of Cisco Switch Administration–Part 1
Introduction
Perhaps you are asked to configure a switch port or see what MAC address is on
what port. Maybe this isn’t something you do every day and need a refresher course
on the most basic Cisco switch administration tasks. Let’s find out how to perform
some basic Cisco switch administration tasks.
Log in
Before you can administer the switch you are going to need some basic information:
What is the switches IP address or DNS name?
What is the username/password you can use to login?
What Ethernet switch port is the device in question connected to?
One option to configure the switch might be a web-based administration interface. If
this is the case, basic configurations aren’t going to be that difficult and perhaps you
don’t need much more help. On the other hand, GUI interfaces aren’t always
available, but on Cisco IOS switches, the Cisco IOS Command Line Interface (CLI)
always is. Plus, in a GUI interface, you won’t be able to configure every possible
configuration as you can with the CLI. For that reason, I encourage you to use the IOS
CLI. The Cisco IOS CLI will be used in this article to perform several common switch
administration tasks.
Showing the switch configuration
Just like on a router, the most common switch IOS command is to show the switch’s
configuration. This will show you the configuration for the entire switch, including all
the Ethernet ports on the switch. To see switch configuration, just type show
running-config, like this:
http://www.router-switch.com/

2. Showing interface port status
Most of the time you are going to a switch, you want to troubleshoot a switch port,
or change a switch port configuration. The quickest way to see the status of your
switch ports is to use the show interfaces status, like this:
This command shows each port: if the port is connected to the device, the VLAN the
port is in, the port duplex, the port speed, and port type. This is an excellent quick
way to see status for your switch ports.
Changing interface speed & duplex
Say that you see that interface Fa0/21 is set to auto (auto negotiate) for its speed but
it needs to be set to 10Mb/sec. To change the speed of any port, you go to interface
http://www.router-switch.com/

3. configuration mode and use the speed command, like this:
On this switch, the possible speeds for the 10/100 Ethernet ports are auto, 10, and
100. On the Gigabit Ethernet ports, you can only tell the switch to either negotiate
port speed or not to negotiate port speed. Once the speed is configured to 10Mb,
you can verify it with the show interfaces fa0/21 status, like this:
As you can see, the speed is now set to 10. To change the duplex of a port, you
perform the same steps but use the duplex command. Duplex can be set to auto, full,
or half.
Enabling and disabling interfaces
To enable and disable interfaces, you use the no shutdown and the shutdown
command in interface configuration mode. Here is an example:
Notice how when the port was shutdown, console messages appear that told you the
administrative state had changed to down, and the line protocol changed to down.
When the port was enabled (no shutdown), the link went down, then the line when
up, then the line protocol changed to up.
You could now do a show interfaces status to see the state of the interface.
http://www.router-switch.com/

4. Summary
Here is what we have learned:
How to show a switch’s configuration
How to show the status of switch interfaces
Change the speed and duplex of a switch port
How to disable (shutdown) and enable (no shutdown) ports on a Cisco IOS
switch
Basics of Cisco Switch Administration– Part 2
Introduction
In Basics of Cisco Switch Administration - Part 1, we covered some of the basics of
Cisco switch administration – how to log in, how to show configuration, how to
change interface speed & duplex, how to enable switch ports, and how to show
switch port status. In Part 2, we will stick to the basics of switch administration by
covering how to save your configuration, how to use the Cisco Network Assistant,
how to speed up switch port startup, and basic VLAN commands.
How to save your switch configuration
In Part 1 of this series, we talked about how to enable/disable ports and how to
change speed & duplex settings. Those are necessary administrator functions but,
when you are done, you must save your configuration. Cisco switches will not
automatically save your changes. If you make these changes and the switch loses
power, those changes are gone. You must save your changes when you are done. The
minimum that is required is to save your changes to the local switch NVRAM. There
are two ways to do this, let me demonstrate:
The textbook method of savings your configuration is: Switch# copy running-config
startup-config However, a legacy command that is short and sweet is:
Switch# wr Both of these commands save your running configuration in RAM to the
file NVRAM:startup-config. When the switch is powered off, the running-config is lost.
The startup-config is read when the switch boots and the running-configis created. I
http://www.router-switch.com/

5. also highly recommend that you save your configuration onto TFTP server, in case
your switch’s local NVRAM is completely lost. Once you have a TFTP server running,
you can easily save your configuration to it like this: Switch#copy running-configtftp
How to use the Cisco Network Assistant
The Cisco Network Assistant (CNA) is a free graphics tool included when you
purchase a new switch. It is used to administer Cisco network devices. CNA is a
feature-rich tool and I cannot possibly go into everything it can do in this short article.
I recommend CNA to anyone who would like a graphical interface for their Cisco
network devices. Basically, CNA gives you an overview screen of your Cisco devices,
like this:
Once you click on Configure then Port Settings, you will see something like this:
From here, you can configure the state, duplex, speed, and other options for your
switch ports. In fact, you can configure most switch features with the CNA. Keep in
mind that for all Cisco switches, there is also the web-based interface. It may be
more limited than what CNA offers. This interface can be accessed directly with your
web browser, or it can be launched via CNA. Here is a sample screenshot of my Cisco
http://www.router-switch.com/

6. 3550 web-based interface:
How to speed up switch port startup
Switch ports could be connected to a variety of devices – other switches, routers,
trunk ports, PC’s, or VoIP phones. Each of these devices has a different configuration.
When a device is connected to a switch port, the switch will attempt to negotiate
settings to match this device. These negotiations include ones for the Dynamic Trunk
Protocol (DTP) (to see if the connected device wants to setup a trunk) and Spanning
Tree Protocol (STP) (Used to ensure that the connection will not cause a loop).
These both take time and will delay the ability of your device (such as a PC) to
transmit and receive data from the network. Most of the time, you are connecting a
PC to a switch and you just want to be able to use the network as soon as possible,
right?
The commands I recommend enabling on all PC/laptop/printer switch ports include
these (All configured in interface configuration mode):
switchport mode access: Sets the switchport into a non-trunking mode
switchportnonegotiate (optional): Disables the switchport from negotiating
spanning-treeportfast: Disables STP negotiations which speeds switchport
forwarding (ensure this switchport only connects to an endpoint device)
http://www.router-switch.com/

7. Basic VLAN commands
Most companies today use Virtual LANs (VLANs). As an administrator, you should
know how to 1) see what device is on what VLAN and 2) to change the VLAN that a
device is in. As you know, if your device is in the wrong VLAN, it won’t be able to
communicate with the servers that it needs to talk to and/or it may be on the wrong
IP subnet. To see what VLAN a device is in, my favorite command is show vlan brief.
Here is an example:
As you can see, this command shows you what VLANs exist on this switch, and what
switch ports are in what VLAN. Now, say that you want to change interface/port
Fa0/21 from VLAN 1 (the default) to vlan 131. Let me show you how to do that:
That’s right, you simply go into interface configuration mode on the interface you
want to change the VLAN, and use the switchport access vlan XXX command. Once
you are done, to verify the vlan membership, just run the show vlan brief command
again, like this:
http://www.router-switch.com/

8. You can see from the command output that Fa0/21 is now a member of VLAN 131.
Summary
Here is what we have learned:
How to save your switch's configuration
How to use the Cisco Network Assistant
How to speed up your switch port startup
Basic VLAN commands
---Original resources from petri.co.il
More CISCO Switch Tips:
How to Configure A Cisco Switch?
General Information of Cisco Switch Commands
Layer 2 Switches & Layer 3 switches
Switch Types and LAN Switching
How to Configure DHCP on a Cisco Router or Cisco Switch?
How to Know What Device is on What Port on a Cisco Switch?
http://www.router-switch.com/