CCIE Pursuit Blog

July 6, 2007

VTP Gotchas: Reloading Switch In Client Mode With No Domain Name

Filed under: IOS,Switching,VTP — cciepursuit @ 12:25 pm

This gotcha probably won’t be an issue in the lab, but it may crop up in real life: If you configure a default switch as a VTP client but don’t configure a VTP domain and then reload the switch, the switch will come back up in VTP server mode.  This could be a problem if you were to configure a default switch as a client and then shipped it to site with the intention of the switch inheriting the current VTP domain name once it was connected to the network.  Although the switch will inherit the VTP domain name, it will be in VTP server mode rather than client mode.

Set VTP mode to client on a defaulted switch:
sw3(config)#vtp mode client
Setting device to VTP CLIENT mode.
sw3(config)#^Z
sw3#sh vtp s
*Mar  1 00:13:33: %SYS-5-CONFIG_I: Configured from console by console

Notice that the VTP domain is NULL:
sw3#sh vtp statu
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 5
VTP Operating Mode              : Client
VTP Domain Name                 :

VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x57 0xCD 0x40 0x65 0x63 0x59 0x47 0xBD
Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00

Let’s write the config and reload:
sw3#wr
Building configuration…
[OK]
sw3#reload
Proceed with reload? [confirm]

*Mar  1 00:13:43: %SYS-5-RELOAD: Reload requestedBase ethernet MAC Address: …

After the switch comes back up – notice the VTP mode:
sw3#sh vtp status
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 5
VTP Operating Mode              : Server
VTP Domain Name                 :

VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x57 0xCD 0x40 0x65 0x63 0x59 0x47 0xBD
Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00
Local updater ID is 0.0.0.0 (no valid interface found)

Okay….let’s try it again, but with a VTP domain configured this time:

sw3(config)#vtp domain CISCO
Changing VTP domain name from NULL to CISCO

sw3(config)#vtp mode client
Setting device to VTP CLIENT mode.
sw3(config)#^Z
*Mar  1 00:28:14: %SYS-5-CONFIG_I: Configured from console by console
sw3#sh vtp statu
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 5
VTP Operating Mode              : Client
VTP Domain Name                 : CISCO

VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0xD3 0x78 0x41 0xC8 0x35 0x56 0x89 0x97
Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00

Write the configuration and reload:
sw3#wr
Building configuration…
[OK]
sw3#reload
Proceed with reload? [confirm]

*Mar  1 00:28:28: %SYS-5-RELOAD: Reload requested

After the switch restores – notice VTP mode is still client:
sw3#sh vtp status
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 5
VTP Operating Mode              : Client
VTP Domain Name                 : CISCO
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0xD3 0x78 0x41 0xC8 0x35 0x56 0x89 0x97
Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00

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1 Comment »

  1. […] revision and asking the Google about some weird questions CCIE Pursuit came up with the asnwers, this one has happened to me IRL where the switch came back up as Server. Also a question about the MD5 and […]

    Pingback by VTP Configuration at Network Ninja — July 19, 2008 @ 8:40 am | Reply


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