VTP storing VLAN data in RAM on client mode switches...

[mitchell helton]

First off I hope this is in the appropriate place, and I apologize in advance if it isn't (just point me in the right direction )...

In the LAN Switching and Wireless CCNA Exploration Companion Guide, chapter 4: VTP (page 185 in the textbook) states:

"A VTP client stores VLAN information for the entire domain only while the switch is on.  A switch reset deletes the VLAN information"

To me, this means if you turn the trunks off and pull the plug (essentially isolating the client switch from other clients/servers), the switch should contain no information about the VTP domain and VLANs.  However, after testing this in packet tracer and with some physical switches, I can't get this to work.  The only way I can get the switch to "forget" about the VLANs is to delete the VLAN.dat file.  So what does the "VLAN information" actually consist of in the itallicized phrase above?

Thanks in advance for reading this over... I hope someone can clear this up for me (and my class!)

[Peter Paluch · Accepted solution]

Hello Mitch,

Don't use the Packet Tracer to discover the fundamental principles. The algorithms used by real routers/switches are not really implemented in the Packet Tracer, rather, the Packet Tracer merely emulates their behavior. The real equipment is your only source of verified information.

Regarding the VTP Client mode and the alleged storage of VLAN database information in RAM only... This has been around for quite a while. I assume that the first CatOS-based switches really worked this way. However, I was not able to reproduce this behavior on any IOS-based switch. All switches running IOS store the entire VLAN database in the file flash:vlan.dat that is persistent (i.e. will be preserved across reboots). On an IOS-based switch, the entire difference between VTP Server and Client modes - as seen from my experience - is only that the Client mode does not allow you to modify the VLAN database contents, and a Client switch does not originate summary advertisements after initial bootup (they are originated only by VTP Server switches).

Best regards,

Peter

[Calin C. · Accepted solution]

Hello!

This discussion may be interesting for you:

https://learningnetwork.cisco.com/thread/4902

Sometimes some descriptions from Cisco may be a little bit confusing and ambiguous. I didn't want to copy paste all discussions from the link provided.

Calin

[mitchell helton]

Calin and Peter, thank you both so very much for your incredibly timely (and accurate) responses.  That other discussion you linked me

is exactly what I was looking for.  Thanks again and have a blessed day!