In complex networks, managing VLANs can be time-consuming and error-prone. The VLAN Trunking Protocol (VTP) is a means whereby VLAN names and numbers can be managed at central devices, with the resulting configuration distributed automatically to other devices. Take for example the network shown in Figure 6-1. This typical three-tier network is composed completely of layer-2 switches. There are 12 switches in all: 2 in the core, 4 in the distribution layer, and 6 in the access layer. (A real network employing this design might have hundreds of switches.)
Figure 6-1. Three-tier switched network
Let's assume that the network has 10 VLANs throughout the entire design. That's not so bad, right? Here's what a 10-VLAN configuration might look like on a 2950:
vlan 10 name IT ! vlan 20 name Personnel ! vlan 30 name Accounting ! vlan 40 name Warehouse1 ! vlan 50 name Warehouse2 ! vlan 60 name Shipping ! vlan 70 name MainOffice ! vlan 80 name Receiving ! vlan 90 name Lab ! vlan 100 name Production
Now, consider that every switch in the design needs to have information about every VLAN. To accomplish this, you'll need to enter these commands, exactly the same each time, into every switch. Sure, you can copy the whole thing into a text file, and paste it into each of the switches, but the process still won't be fun. Look at the VLAN names. There are two warehouses, ...