DHCP Service

R1(config)#ip dhcp excluded-address 10.1.10.1 10.1.10.10

R1(config)#exit

R1(config)#ip dhcp pool vlan10

R1(dhcp-config)#network 10.1.10.0 255.255.255.0

R1(dhcp-config)#default-router 10.1.10.1

R1(dhcp-config)#dns-server 10.1.1.254

R1(dhcp-config)#end

Enable CDP Protocol

CDP (Cisco Discovery Protocol) is a proprietary Layer 2 network discovery protocol developed by Cisco. It allows Cisco devices (such as switches, routers, and access points) to discover each other on the network and gather information about their neighbouring devices. This protocol operates at the Data Link Layer (Layer 2) of the OSI model and is used for exchanging information about network topology and device attributes such as device name, IP address, and hardware capabilities.

Enabling CDP on a Cisco switch allows administrators to identify and troubleshoot network issues.

When CDP is enabled on a Cisco switch, it will periodically send out CDP packets to its directly connected neighbours and receive CDP packets from them as well.

We can enable the CDP neighbours on the switch and router as shown in the scripts below:

Implement Helper

In Cisco networking, the helper address on a Layer 3 switch is primarily used to enable DHCP relay for a VLAN or subnet. This feature is especially important when DHCP servers are located on a different network segment than the clients.

Here's how it works and why it's useful:

Facilitates DHCP Relay: When devices in a VLAN send DHCP requests, these requests are broadcast-based, and broadcasts don't cross Layer 3 boundaries by default. By configuring a helper address on the multilayer switch, you can relay these broadcasts to a specific DHCP server on another subnet. The switch forwards the request as a unicast message to the DHCP server, ensuring the client receives an IP address.

Supports Centralized DHCP Servers: In larger networks, having DHCP servers centrally located is often preferable. With the helper address, the Layer 3 switch can route requests to a DHCP server outside the client’s VLAN, simplifying IP address management.

Allows Multiple Protocols: Though commonly used for DHCP, the helper address can relay other types of broadcasts, like TFTP or DNS, by specifying protocols to forward in the configuration.

In short, the intention of using a helper address is to allow devices on a VLAN to receive DHCP addresses or other services from a server outside of their local subnet, enabling efficient network configuration and scalability.

In our example we use helper address to find the DHCP server on a different subnet.

Below we are adding the helper address for each VLAN (VLAN 10, VLAN 20). We are specifying the IP address of the helper.

Static Routing on Multilayer Switch

On the router we are ready to create a static route to be able to send packets to and from the switch.

The static route settings are a relatively simple task. We need to specify the network we want to go with the subnet masks and the next hop address. In our case, it will be the IP address of the router of each VLAN and router IP address. 

Check Connectivity

A router R1 should be able to ping with the switch virtual interfaces of VLAN 10 and VLAN 20 to confirm successful setup. Supposedly you will lose the first packet due to the ARP process, but the second ping will be fully successful with a100% rate of completion.

Routing path from the switch to loopback on the router

We need to add an extra route to the loopback on the router with the purpose of forwarding packets to the router using a static routing protocol.

First we need to enable routing on the multilayer switch. The command for enabling routing on the switch is "ip routing."

Next, we should add a static path to the loopback of the router IP with the destination of the router's default gateway (router’s interface). It sounds complicated, but it is not. In other words, we need to go to the destination on loopback through the router interface. This will help ensure proper routing of traffic between the loopback and the default gateway.

We are now prepared to verify whether the DHCP service is operational and operational by utilising router 1's DHCP settings commands.