Create VLAN In Text Mode

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Jul 2, 2009 5:39 AM
Jul 2nd, 2009

On a VTP sever vlan information is not stored in the "text mode" config. Despite configuring "text mode", it’s still in binary mode stored in a separate binary block in NVRAM.

If we allowed creation of vlan information in "text mode" it would be possible to create a DoS attack e.g each time a vtp-server switch received a VTP update it involves some CPU processing overhead and maliciously formed VTP advertisements could cause issues. So "text mode" was designed to keep VLAN information in binary mode and not save it in the text mode.

The command show vlan is required to see the VLAN information. To create or to make any changes to the VLAN the below given procedure may be followed.

  1. set config mode text.
  2. make any configuration changes you would like to make.
  3. backup the text config. (So you will have configuration w/o vlan information)
  4. remove one linecard. (This will reduce the configuration, but vlan information would be same)
  5. set config mode binary (This time it should let you convert binary since you have removed a linecard)
  6. backup the binary config. (So you will have all configs + vlan information)
  7. insert the linecard back in.
  8. set config mode text.
  9. upload previously saved text mode config.

In "text mode" you will not be able to save vlan creation information. You will always have to change the config mode to binary and then save the config, to get vlan creation information.

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