L2 Mock LAB- VTP Modes, DHCP Server, InterVLAN Routing andWAN Failover (IPSLA)

5 min readMay 27, 2023

Topics Covered

VTP Modes(Server, Client)
InterVlan Routing
DHCP Server
Primary-Backup WAN (IP SLA)
Convergence and Integration of Topologies

TOPOLOGY:

VTP:

To ensure that a VLAN exists between every pair of Trunked switches, an administrator must manually create all the needed VLANs on each of the switches individually. Cisco’s VLAN Trunking Protocol (VTP) provides an easier method for maintaining consistent VLAN configuration throughout the switched network.

VTP is a protocol used to distribute and synchronize identifying information about VLANs configured throughout a switched network. Configurations made to a single VTP server are propagated across trunk links to all connected switches in the network. VTP enables switched network solutions to scale to large sizes by reducing the network’s manual configuration needs.

VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency throughout a common administrative domain by managing the additions, deletions, and name changes of VLANs across networks. VTP minimizes misconfigurations and configuration inconsistencies that can cause problems, such as duplicate VLAN names or incorrect VLAN-type specifications.

A VTP domain is one switch or several interconnected switches sharing the same VTP environment. A switch can be configured only in one VTP domain.

VTP Modes:

VTP operates in one of three modes:

Server mode
Client mode
Transparent mode

The default VTP mode is server mode, but VLANs are not propagated over the network until a management domain name is specified or learned and Trunking has been established. A Catalyst switch operating in the VTP server mode can create, modify, and delete VLANs and other configuration parameters for the entire VTP domain. In server mode, VLAN configurations are saved in the Catalyst nonvolatile random-access memory (NVRAM). When you make a change to the VLAN configuration on a VTP server, the change is propagated to all switches in the VTP domain. VTP messages are transmitted out all trunk connections, such as ISL.

A device operating as a VTP client cannot create, change, or delete VLANs. A switch in client mode does send VTP messages, however. A VTP client does not save VLAN configurations in nonvolatile memory.

In both client and server mode, the switches synchronize their VLAN configuration to that of the switch with the highest revision number in the VTP domain.

Configurations:

VTP-Server2:

left_Distribution_SW(config)#vtp mode server

Verification:

Command to verify VTP status is “Show vtp status”.

VTP-Server1:

right_Distribution_SW(config)#vtp mode server

Verification:

Command to verify VTP status is “Show vtp status”.

VTP-Client:

In this topology we created VLANs on server and it propagates and advertise to all neighboring switches which is in the same vtp domain and all switches synchronize their database with those switches database which as highest revision number. And we cannot create VLAN on switch which has VTP client mode.

SW6(config)#vtp mode client

Verification:

Command to verify VTP status is “Show vtp status”.

Configuration between VTP-Server and VTP-Client Switches:

The link between switches which is in VTP server mode and VTP Client mode is trunk and we have statically configure those link in the topology as trunk.

One of the switch configuration is pasted:

As SW5 and other access layer switches are in VTP client mode so we cannot create VLAN on those switches:

InterVLAN Routing(ROAS):

Inter-VLAN routing is a process of forwarding network traffic from one VLAN to another VLAN using a router or layer 3 device.

By using VTP we have already flood VLANs 10,20 to the VTP clients. So we will create Sub interface on R7(leftEdgeRouter) and R8(rightEdgeRouter).

Configurations:

Verification:

DHCP Server:

Dynamic Host Configuration Protocol (DHCP) is a network protocol that enables a server to automatically assign an IP address to a computer from a defined range of numbers (i.e., a scope) configured for a given network.

In our topology, we have one DHCP server(R7).

R8:

We configured Router interface as a DHCP helper so it will allow the broadcast for discovery of DHCP server through the router as router do not allow to broadcast to pass through it.

interface GigabitEthernet0/2.10

encapsulation dot1Q 20

ip address 192.168.110.1 255.255.255.0

ip helper-address 1.1.1.1

interface GigabitEthernet0/2.20

encapsulation dot1Q 20

ip address 192.168.220.1 255.255.255.0

ip helper-address 1.1.1.1

VPC20:

As seen, the client which is in VLAN 20 is getting IP from pool which is defined for VLAN 20.