Archives for March 2013

This is how your LAB will need to be configured. You can download this lab via Packet tracer here: Cisco Packet Tracer VLAN Lab.

There are a couple of definitions I think you should know:

Default Switch Behavior

The default behavior of a switch is to forward a broadcast out of every single port except the port on the switch that it came in on. Ie. The switch only has one broadcast domain by default… VLAN1

VLAN’s

VLAN’s allow you to breakup the switch into separate virtual local area networks. VLAN’s can help us save resources by:

1. Limiting broadcasts… particularly the broadcasts to hosts that DO NOT need them. You do this by increasing the number of broadcast domains.
2. Prevent broadcast storms that render a switch virtually useless
3. Help you logically segment the LAN to increase security. ie. Separating departments on a LAN so “accounting users” will not talk with “building maintenance users”.

VLAN Commands

To Show the vlan’s on a given switch you want to use the command:

• show vlan brief

You will see that that default VLAN has already been created (VLAN1). There is also the special 1002-1005 VLAN’s created as well. You can create any VLAN in between 2-1001.

One thing that you might throw you for a loop the first time you see it is when you run the “show vlan” command and there are ports missing. This normally means that someone has setup a thing called trunking on the switch already. More on this later in the post.

First you should make sure all hosts can ping each other on the network.

To put a particular port into a VLAN you need to run several commands on the switch. Here are the commands to get all 4 ports configured as per our graphic.

First get into config mode and select the port:

• conf t
• int fast 0/1

Run the commands to put the port into “Access Mode” and tell the port what VLAN to it should be apart of. If there is no VLAN already created this command will actually automatically create that VLAN for you.

• switchport mode access
• switchport access vlan 2

You will need to do this for the rest of the ports as shown in the network layout graphic. An easy way to do this is by using the “up arrow” to repeat commands and change the characters that are different.

• int fast 0/2
• switchport mode access
• switchport access vlan 3
• int fast 0/3
• switchport mode access
• switchport access vlan 2
• int fast 0/4
• switchport mode access
• switchport access vlan 3

Run “show vlan brief” now to verify that commands were successful. You should now try and ping the different hosts. If you’ve set things up correctly “.1 and .3” should be able to ping each other. “.2 and .4” should be able to ping each other. No other pings should go through.

You might be wondering how we can get traffic to talk to each other on VLAN2 and VLAN3. To do this we need to work with a layer 3 switch. To do this we will need to use a technique called “router on a stick” or use a layer 3 switch instead of a Layer 2 switch. What makes a Layer 3 switch a Layer 3 switch is their ability to run routing protocols (ie. eigrp or ospf).

Supposedly the CCNA will not ask questions on the L3 switches so it’s important that you learn about “router on a stick”. I will eventually create a tutorial on “Router on a stick”.

Your switch will keep a separate switching table for each VLAN. To see this type the command:

• show mac-address-table dynamic vlan 2

So what happens if you have multiple switches. How do we deal with multiple VLANs? We deal with this with a technology called “Trunking”. Please see the next article on “How to setup Truking on a Cisco Switch”.

This is going to be a basic guide for you. Essentially it will be for people too lazy to pickup and read the “Getting Started Guide”. I was pleasantly surprised how similar the commands on this switch were to a cisco switch! If you know anything about cisco switch language IOS than you will feel right at home! These switches are branded Dell are actually made by Nortel.

Needed

1. Dell ships a serial to console cable. My ultrabook didn’t come with a serial connection. I ended up getting a Keyspan USB to Serial converter. Check device manager to see what COM port you are using.
2. You will need to make sure you have some software installed on your machine that you can talk to the switch via the console. I recommend that you use the famous PuTTy Software. I recommend that you just download the all-in-one installer.
3. Dell puts the serials at the back of the switches. I recommend that you take a dymo labler and mark down the serial etc and put it in a place where you will be able to easily see it. You can also get it from the Web Gui or console if needed as well.
4. Plan out the IP addresses for each switch.
5. Plan out the names of the switches

Physically connecting everything:

NOTE – Do not turn on switch until told to!

1.) Plug in your cables into your computer. Most people I am assuming will need a USB to Serial convert.

2.) Check what COM port you are using:

3.) Open PuTTY and make sure the settings are as follows:

Serial:

NOTE – These should all be the defaults. Make sure that you have the same speeds listed as well.

Session:

NOTE – Enter in the serial line what ever COM port you are using via step #2. I save my session and called it “Dell Switch” so that I can easily connect again to the switch.

4.) Hit OPEN in the Putty Session window. This will open a windows that will look similar to a command prompt.

5.) Plug in the power cable to the switch. You will notice the switch will start to boot.

6.) Hit “Y” to setup the switch

7.) I setup SNMP on my switch. I chose the default: Dell_Network_Manager for the SNMP community string.

8.) It will ask you to setup the IP address, Subnet mask, Gateway, Username and password. It will also ask you if you only want certain computer allowed to make changes to the switch.

9.) Once you are done it will ask you to save the configuration. Hit “Y”.

10.) Once done you will need to setup the hostname of the switch:

• enable [enter]
• configure [enter]
• hostname <switchname> [Enter]

You can verify that the change has been made by hitting “Ctrl+z”

• Type “show running”
• Verify that the hostname is in the config file.

Save the changes

• Type: “wr”
• When asked if you want to save hit “yes”.