Outdated or invalid documentation of whether VTP client saves VLAN configurations?

[amharsaputra]

Here is a link from the latest IOS of Catalyst switch:

http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst3750x_3560x/software/release/15.0_2_se/configuration/guide/swvtp.html#wp1205076

Quote:

In VTP versions 1 and 2, in VTP client mode, VLAN configurations are not saved in NVRAM.

I find that statement (or similar meaning statements) everywhere, from CNAP, Cisco Press, Cisco Documentation. I haven't found a way to prove that statement.

Once I learnt that “saved in NVRAM” means the switch will save the VLAN configurations as vlan.dat in flash (we can verify it with “show flash”). So because the VTP client doesn’t save VLAN configurations in NVRAM, the VLAN information will be lost if the VTP client lost connection to VTP server AND reloaded. But according to my experience, that is not the case. Once a VTP client has synchronized its VLAN configuration with VTP server, it will have vlan.dat also, and will retain VLAN information even if I disconnect link to VTP server and then I reload the VTP client with no links to any other switch. (I’ve just simulated this situation with 2960 and 2950).

I find a discussion in this forum that confirms that (https://supportforums.cisco.com/message/3309465).

And I find conflicting statement (compared to the first link) from Cisco documentation:

http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080890613.shtml#topic2

Quote:
Configuration changes in CatOS are written to NVRAM immediately after a change is made. In contrast, Cisco IOS® Software does not save configuration changes to NVRAM unless you issue the copy running-config startup-config command. VTP client and server systems require VTP updates from other VTP servers to be immediately saved in NVRAM without user intervention. The VTP update requirements are met by the default CatOS operation, but the Cisco IOS update model requires an alternative update operation.

For this alteration, a VLAN database was introduced into Cisco IOS Software as a method to immediately save VTP updates for VTP clients and servers. In some versions of software, this VLAN database is in the form of a separate file in NVRAM, called the vlan.dat file. You can view VTP/VLAN information that is stored in the vlan.dat file for the VTP client or VTP server if you issue the show vtp status command.

This is the first time I find a statement from Cisco that implies VTP client saves VTP configuration (updates) in NVRAM too. So in this statement, VTP updates are immediately saved in NVRAM, from the time of CatOS until the time of IOS, both for VTP clients and servers. I found this in troubleshooting section. Why on earth in Cisco configuration guide section (and any other references) the message is not the same??

Is it safe to say that Configuration Guide documentation of VTP mode client is invalid? So why Cisco keeps that documentation for years, in every Cisco IOS release configuration guide? How can we notify Cisco of this mistake so the documentation gets updated?

[Giuseppe Larosa · Accepted solution]

Hello Amhar,

your findings are correct I have seen too persistency on  IOS switches in VTP client mode.

Another common misunderstanding is that a switch in VTP client mode can't override the Vlan database in the VTP domain if its revision number is higher then that in the VTP domain. When connecting a switch to a production network we need to be careful about revision number even if the switch is in VTP client mode, because it can override the Vlan database.

Documentation should be updated you are right including both configuration guides and course books.

A sentence like the following would be enough:

Actually in IOS implementation of VTP also switches in client mode create a local vlan.dat file in NVRAM. This allows for VTP updates to be stored immediately in NVRAM without waiting for a saving of configuration file.

Hopefully someone of the Cisco guys that participate in the forums may rise a ticket for this.

Hope to help

Giuseppe

[amharsaputra]

Thank you for your response Giuseppe.

Yes I really hope the documentation gets updated to end confusion. Hopefully someone can raise this issue to Cisco. Just now I use Website Feedback found in this link:

http://www.cisco.com/web/siteassets/contacts/index.html

I don't know whether the feedback will get a response though.