To establish trunking using VTP among cascaded switched network

                  Fig: cascading between  two switches
Now, consider the  figure. In this figure there are two switches and  both are connected to each other. Let us assume as per the diagram interface 12 of switch 1 is connected to interface 18 of switch 2. Now, we have to establish vlan trunking so that switch 2 can access vlan information of switch 1

//To configure switch 1 as VTP server:

switch# conf t
switch(config)#vtp mode server
switch(config)#vtp domain iop
switch(config)#vtp password 123456#
switch(config)#int fa0/12
switch (config-if)#switchport mode trunk
switch(config-if)#^Z

//To configure switch 2 as VTP client:
switch#conf t
switch(config)#vtp mode client
switch(config)#vtp domain iop
switch(config)#vtp password 123456#
switch(config)#int fa0/18
switch(config-if)#switchport mode trunk
switch(config-if)#^z

//To see vtp status:
switch#sh vtp status

This command would give information about VTP domain, mode(whether sever or client mode) & many more

//To see trunk link
switch# sh vtp counter
This command would give the information that vtp trunk link is established between interface 12 of switch 1 & interface 18 of switch 2

Now, members of switch 2 can access vlan information of switch 1 and can be put on the same vlan created on switch 1. But switch 2 can't create or add vlan.
Through  this we can manage vlan centrally

Now, Consider Fig 2:

fig 2: Two switches connected with each other parallely

The fig 2 is the best scenario of cascading switched network. People think that this would result in a loop but this is managed by Spanning Tree Protocol. Spanning Tree Protocol is by default supported by cisco switches.

To explain this further let us assume that interface 11 of switch1 is connected to the interface 19 of switch 2

Server switch(Switch 1)
switch# conf t
switch(config)#int fa0/13
switch (config-if)#switchport mode trunk
switch(config-if)#^Z

Client switch(Switch 2)
switch# conf t
switch(config)#int fa0/19
switch (config-if)#switchport mode trunk
switch(config-if)#^Z

Now, As per the scenario interface 12 of switch 1is coonected to interface 18 of switch 2 & interface 13 of switch 1 is connected to switch interface 19 of switch 2. Now, in Cisco switches Spanning Tree Protocol by default blocks one port of anyone switch to avoid loop formation & if one line fails then second line automatically takes up whole thing. The algorithim which supports spanning Tree Protocol is
called Spanning Tree Algorithim