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Switches / Hubs

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Solutions

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A switch is a device that filters and forwards packets of data between LAN segments. Switches operate at the data link layer or the network layer of the Open Systems Interconnection (OSI) Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs. A hub is a connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports; when a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

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This article will show how Aten was able to supply easy management and control for Artear's video walls and wide range display configurations of their newsroom.
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Flash Dir Head

WARNING:  If you follow the instructions here, you will wipe out your VTP and VLAN configurations.  Make sure you have backed up your switch!!!


I recently had some issues with a few low-end Cisco routers (RV325) and I opened a case with Cisco TAC.  The basic problem was that I couldn't get the routers to route traffic in this kind of environment:



I wasn't using the firewall feature; just routing.  (The firewalls in the diagram were ASAs).

Well, the Cisco engineer couldn't figure out what was wrong, so I pulled a couple of routers out of the network and set up a small lab so the engineer could remote in and play with it.  The lab environment looked like this:



The networks were all connected with a Cisco 2950 24-port switch using VLAN and a Cisco 2601 configured as a router-on-a-stick.


I know... really old hardware, but it was just lying around collecting dust and it could do what I needed, so why not?


When I attempted to blank out the config, I couldn't get rid of the VLANs... which reminded me how frustrating VTP can be.


For example, years ago, I borrowed one of these 2950's from the datacenter where I have a few cabinets.  Before I returned it, I wiped the config.  Six months later, I get a call from their head engineer informing me that I had taken down the entire datacenter.


VTP configuration information is stored in the VLAN database, which is NOT deleted when one clears the config.  I had actually used VTP in my network, but they didn't and the VTP operating mode of all of their switches were still the default - "server".  So, when they put that switch back into production, my VTP config was pushed out across their network and every single VLAN database on every single switch was overwritten with my VLAN config.


The VLAN database is stored as a file in the flash memory.  To see it, go into privileged mode and issue a directory command for flash:



The VLAN database is stored in the file "vlan.dat".


Since Cisco represents the state-of-the-art for networking equipment, one could assume the VTP configuration could be reset by issuing a command such as "clear config vtp".  Of course, one would assume incorrectly.


You actually have to delete the file:

 


Once you've done that, you should be good to go.  Reload the switch and you'll find the VTP (and VLAN) configuration has been removed.


If you found this helpful, please click the blue "thumbs up" below!

1
ATEN / Arrow Electronics Case Study
Arrow Electronics was searching for a KVM (Keyboard/Video/Mouse) switch that could display on one single monitor the current status of all units being tested on the rack.
0
I eventually solved a perplexing problem setting up telnet for a new switch.  I installed a new Cisco WS-03560X-24P switch connected to an existing Cisco 4506 running a WS-X4013-10GE Sup II-Plus.

After configuring vlans and trunking,  I could not telnet to the new switch from my existing environment.   I could ping the new switch from my existing environment, a PC workstation attached to the new switch could ping all of my network devices and internet addresses, a workstation connected to the new switch could also get a DHCP address from Windows servers in my existing environment, and I could also RDP to the workstation on the new switch from my existing environment.  

But, I could not telnet from the same PC used for RDP in the existing environment.  I could only telnet from the PC connected to the new switch.  I tried using both MS telnet and Putty.

Here is the problem and the solution:

I had configured 3 vlans on the new 3560 switch
vlan 1  - managment
vlan 6 - new PC and voip vlan
vlan 11 - existing voip network

I had configured the new vlan 6 on the existing 4506 switch and set up trunking between the two switches.

Problem:  
Vlan 3 used in the existing environment was not configured on the new switch.  I was trying to connect from vlan 3 using MS telnet or Putty from a connection on the existing 4506 switch.

Solution:
As soon as I configured vlan 3 on the new 3560 switch I was able to telnet/Putty from my PC …
0
 
LVL 1

Expert Comment

by:patrickh99
Comment Utility
This is a common error.  Configuring a vlan on an access or trunk port or even an SVI does not create the vlan on the switch, therefore no traffic can flow through that vlan until it is created, per the procedure you detailed.

Nice write-up.
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This tutorial will go through the steps required to write a script that will back up the configuration settings of a HP-ProCurve switch.

You will need to get the following things to follow this tutorial:


Telnet Scripting Tool e.g. TST10.exe
Any text editing tool
TFTP Server(I am using TFTP 32 for this tutorial)
List of IP addresses for your switches

1. Installing and starting TFTP32


First thing we need to do is download the software from their web page: "http://tftpd32.jounin.net/tftpd32_download.html".  We need to download "tftpd32 standard edition (zip)".  Create a new folder and name it "SwitchesBackup" open the zip file and copy the .exe and .ini files into the folder since that's the only files we need for TFTP.

Now start the tftpd32.exe and you will be prompted with a Windows firewall warning. We need to allow it to work. After that the program should start up:You will need to save this IP.

2. Getting TST10


Next we will need TST10.exe for the Telnet connection. You can get this file at: http://jerrymannel.com/blog/2008/11/11/telnet-scripting-tool-aka-tst10exe/
scroll down and you will find the file as a .exe or zip; after downloading it place the .exe in the folder "SwitchesBackup".

3. Writing the Script


Now that we have both executables in the folder called "SwitchesBackup". We can continue and start making the script. …
0
 
LVL 15

Administrative Comment

by:Eric AKA Netminder
Comment Utility
DAlper,

Congratulations! Your article has now been published.

ericpete
Page Editor
0
 
LVL 1

Expert Comment

by:speeDemon
Comment Utility
What type of script is this, I named the file "ProcurveBackup.vbs and I get an invalid character error at line 14 char. 29....
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I see many questions here on Experts Exchange regarding switch port configurations and trunks. This article is meant for beginners in the subject to help to get basic knowledge about Virtual Local Area Network (VLAN) and port-configurations in Cisco Catalyst switches.

An Ethernet-frame (packet) can be either tagged or untagged. The default is untagged. When a frame is tagged, an extra 802.1q header is placed first in each frame, containing a VLAN id, a number normally between 1 and 2004. Each VLAN is a separate broadcast domain and should use different IP network addressing. As you probably know, a switch cannot pass traffic between different VLANs.

A switch port can be configured either as an access port or as a trunk. An access port sends and receives traffic to/from one single VLAN, untagged. This is the normal thing for connecting PCs and other non trunk-aware equipment into a switch. The default configuration for a switch port is to be configured as an access port in VLAN 1. It looks like this:
Interface FastEthernet0/1
 switchport mode access (default, invisible)
 switchport access vlan 1 (default, invisible)
!

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In case of connecting non trunk-aware equipment to another VLAN than default VLAN 1, this is specified with the switch port "access vlan" command which is now visible:
Interface FastEthernet0/1
 switchport mode access (default, invisible)
 switchport access vlan 2
!

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To configure a trunk, change the switch mode to trunk. The default is to carry all VLANs.
Interface FastEthernet0/1
 switchport mode trunk
 switchport trunk allowed vlan 1-2004 (default, invisible)
!

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To filter which VLANs should be available on the trunk, add the "allowed vlan" command:
Interface FastEthernet0/1
 switchport mode trunk
 switchport trunk allowed vlan 1,5-7,9
!

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2
The worst thing when starting a new job is when the previous Network Administrator left behind no documentation. How do you get into the devices? If you've been in this situation or just accidently mistyped your password, this article will hopefully shed some light on your problem.
 

1. Console to the device

Console into your switch using a console cable an a program such as HyperTerminal, CRT, SecureCRT or Putty.

2. Enter recovery mode

Unplug the power cable. Then, plug the power cable back in WHILE holding the mode button located on the front panel of the switch.

Note: For 2900/3500XL and 3550 Series switches, release the mode button after the LED above port 1 turns off. For 2950 Series switches, release the mode button after the STAT LED goes out.

3. Initialize the flash

 

switch: flash_init

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4. Issue the load_helper command

 

switch: load_helper
switch:

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5. View the flash

 

switch: dir flash:

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6. Rename the current configuration file

 

switch: rename flash:config.text flash:config.old
switch:

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7. Boot the device

Type "boot" and press enter.

switch: boot

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8. Cancel the the system setup

 

--- System Configuration Dialog ---
At any point you may enter a question mark '?' for help.
Use ctrl-c to abort configuration dialog at any prompt.
Default settings are in square brackets '[]'.
Continue with configuration dialog? [yes/no]: n 


Press RETURN to get started.

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9. Enter enabled mode

 

Switch>en
Switch#

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10. Rename the configuration

 

Switch#rename flash:config.text system:running-config

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11. Copy the configuration into the running-configuration

 

Switch#copy flash:config.text system:running-config

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12. Change the password

 

Switch#configure terminal
Switch(config)#no enable secret 
Switch(config)#enable password NEWPASSWORD

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13. Save your new password

 

Switch#write memory

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2
 
LVL 1

Administrative Comment

by:Vee_Mod
Comment Utility
jjmartineziii,
This appears to be substantially nothing more than the information already provided by Cisco:
http://www-tss.cisco.com/eservice/compass/common/activities/password_cat_2950.htm

Do you have anything further to add that they don't cover already?

Vee_Mod
Experts-Exchange Moderator
0

Switches / Hubs

20K

Solutions

17K

Contributors

A switch is a device that filters and forwards packets of data between LAN segments. Switches operate at the data link layer or the network layer of the Open Systems Interconnection (OSI) Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs. A hub is a connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports; when a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.