CCNA and CCNP candidates who have their own Cisco home labs often email me about an odd situation that occurs when they erase a switch's configuration. Their startup configuration is gone, as they expect, but the VLAN and VTP information is still there!
Laptop Battery Sounds strange, doesn't it? Let's look at an example. On SW1, we run show vlan brief and see in this abbreviated output that there are three additional vlans in use:
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Thinkpad SW1#show vlan br
Interesting traffic brings the link up; by default, any traffic can cross the link once it's up; a lack of interesting traffic is what brings the link down. In Part II of this tutorial, we'll take a look at some common scenarios that make the ISDN link stay up, and what can be done about it. Chris Bryant, 12933, is the owner of The Bryant Advantage ( //www.thebryantadvantage.com), home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, Ultimate CCNP Study Packages, and CCNA CBT video training. Pass the CCNA exam, BSCI exam, and BCMSN exam with Chris Bryant, 12933!
Microsoft
10 VLAN0010 active
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Laptop Computers 20 VLAN0020 active
Occasionally, during your CCNA and CCNP studies, you'll run into a term that just doesn't quite make sense to you. (Okay, more than occasionally!) One such term is "reverse telnet". As a Cisco certification candidate, you know that telnet is simply a protocol that allows you to remotely connect to a networking device such as a router or switch. But what is "reverse telnet", CCNP home lab setup
Laptop Computer 30 VLAN0030 active
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Desktop Computer We want to totally erase the router's startup configuration, so we use the write erase command, confirm it, and reload without saving the running config:
Notebooks SW1#write erase
Lenovo Erasing the nvram filesystem will remove all configuration
files! Continue? [confirm]
Hard Drive
[OK]
Travelstar Erase of nvram: complete
Gateway 00:06:00: %SYS-7-NV_BLOCK_INIT: Initalized the geometry of nvram
Laptop Parts SW1#reload
Software System configuration has been modified. Save? [yes/no]: n
Hard Drives Proceed with reload? [confirm]
Electronics The router reloads, and after exiting setup mode, we run show vlan brief again. And even though the startup configuration was erased, the vlans are still there!
Canon Switch#show vlan br
Desktop Pc
10 VLAN0010 active
Desktop Computers 20 VLAN0020 active
Think Pad 30 VLAN0030 active
Repair The reason is that this vlan and VTP information is actually kept in the VLAN.DAT file in Flash memory, and the contents of Flash are kept on a reload. The file has to be deleted manually.
Data Recovery There's a little trick to deleting this file. The switch will prompt you twice to ask if you really want to get rid of this file. Don't type "y" or "yes"; just accept the defaults by hitting the return key. If you type "y", the router attempts to delete a file named "y", as shown here:
Cisco Switch#delete vlan.dat
Keyboard Delete filename [vlan.dat]? y
Monitor Delete flash:y? [confirm]
Desktop %Error deleting flash:y (No such file or directory)
Infosys
Switch#delete vlan.dat
Refurbished Laptops Delete filename [vlan.dat]?
Wipro Delete flash:vlan.dat? [confirm]
Lap Top
Switch#
Refurbished The best way to prepare for CCNA and CCNP exam success is by working on real Cisco equipment, and by performing lab tasks over and over. Repetition is the mother of skill, and by truly erasing your VLAN and VTP information by deleting the vlan.dat file from Flash, you'll be building your Cisco skills to the point where your CCNA and CCNP exam success is a certainty.
Memory
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