CCIE R&S Written Section 1.20 – Implement VLAN and VTP


Standard VLANs from 1 – 999 Extended VLANs from 1000 – 4094
To create VLANs 1000 – 4094 you must be in VTP Transparant mode in you’re running VTP 1 or 2, otherwise you must be using VTP v 3 to create VLANs in this range.

If a client, SW2, sees two VTP Servers SW1 and SW3 which are not themselves directly connected, but are connected through SW2 and SW2 loses connection with SW1, then the client receives an update to add vlan 999 from the SW3, the client will UPDATE the SW1 that’s been offline with that new VLAN information when it comes back on!

SW1, will see that its configuration revision number is lower than SW2, and even though SW2 is a “client” SW1 will use the updated information in the VTP advertisement from SW2 to update to its VLAN database, and get in “sync” with the rest of the VTP domain, including knowing about VLAN 999. So even though Clients cannot modify the VLAN database, they can pass changes to other servers if the configuration revision is higher than the server assuming the security credentials – domain and VTP password are correct.

Default for a new switch is to startup in VTP Server mode with a NULL domain name and no password.
If a switch in this condition is connected using a trunk port with a switch to a VTP domain with no password, that switch will automagically assume a role within that domain and add information from that domain to its VLAN database.

Should a switch with the correct domain name, no password (or the correct current password for the domain) and a higher VTP revision number attach itself to the network – client OR Server remember! – that switch will overwrite the other swtiches VLAN database information with the information that it holds, which could be disastrous!

#show vtp status
#show vtp password
(config)#vtp version 1|2
(config)#vtp domain NAME
(config)#vtp password PASSWORD

These are the main configuration commands for VTP.

VTP pruning

VTP pruning can only be enabled on switches that are VTP 2 capable. They don’t actually have to be running VTP v2, but they must be capable.

Enabling VTP pruning on the VTP Server in a Client/Server topology will enforce pruning throughout the VTP domain.

To enable VTP Pruning, either visit the server or transparant mode VTP switch and enter:-

(config)#vtp pruning

Confirm it’s in effect using simply

#show vtp status

In the output of this command you should expect to see

VTP Pruning Mode                : Enabled

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