While the CCNA provides a brief overview of the three-tier network concept, I chose to build my own three-tier network from the ground up. This decision allowed me to apply the skills I had gained through the CCNA and integrate them into a project. I drew inspiration from Keith Barker’s Three-Tier Network for this topology. However, as you’ll discover later on, I made the decision to run my Core and Distribution layers on Layer 3 with a routing protocol, in comparison to Keith’s configuration at Layer 2.
This topology includes the use of Layer 3 switches in the Core and Distribution Layers allowing for the use of routing protocols and IP routing in layer 3 as well as VLANs and Switch Virtual Interfaces (SVIs) in layer 2. It also includes an ISP connection and an outside server that my hosts can ping. There is also a DHCP server in place to allow my hosts to request addresses for their VLANs. I’ve implemented HSRP at the Distribution Layer for redundancy as well as multiple interfaces per network device for added redundancy.
I started by configuring IP addresses on the interfaces connecting the Core and Distribution layers. I used the 10.10.X.X network to keep it simple. Additionally, I configured the interface on C1 leading to the ISP and the DHCP server on C2. I also went ahead and configured the addresses and static routing on the ISP router, ensuring that by the end of the project, I would be able to successfully ping them.
Starting from the top and working my way down, I began by configuring OSPF between the Core and Distribution layers. I advertised the network 10.10.0.0 using the first two octets as the network and the last two as hosts, simply because it doesn’t need to be a very specific network in this scenario. I configured the 10.10.0.0 0.0.255.255 network on both Core and all Distribution Switches.
In Block 1, I assigned VLANs 10 and 20 for Sales and Finance on switches D1, D2, SW1 and SW2. Meanwhile, in Block 2, switches D3, D4, SW3 and SW4 are configured with VLANs 30 and 40 for HR and Marketing.
Continuing the configuration, I established Switch Virtual Interfaces (SVIs) for VLAN 10 and 20 on D1 and D2, while on D3 and D4, I set up SVIs for VLAN 30 and 40. To enhance redundancy, I configured HSRP for each SVI. I assigned virtual IP gateways 192.168.10.1 and 20.1 for VLANs 10 and 20, 30.1 and 40.1 for VLANs 30 and 40, aligning with their respective VLAN numbers.
I enabled trunking on the ports connecting the Distribution and Access layer switches, enabling the flow of multiple VLANs across the two layers, allowing HSRP to proceed with its active and standby router selection.
I proceeded by adding the network between the Distribution and Access layers into my OSPF configuration. This allows the Distribution Switches to advertise the 192.168.X.0 network to the Core layer, covering the hosts in VLAN 10, 20, 30, and 40.
To enable routing to the ISP and the internet, I configured a default static route. To include this default route in my routing table, I employed the command “default-information originate” in my OSPF configuration.
Given that the CCNA covers DHCP through a router rather than a server, I decided to configure DHCP on my router connected to C2. I named each DHCP pool after the respective VLAN numbers, excluded the initial 50 host addresses and assigned the HSRP virtual IP address as the default router for the configuration.
To allow hosts to discover DHCP, I configured the ip helper-address command into my SVIs. After a couple of attempts to request DHCP, my hosts received their addresses.
Finally, I tested a ping to the external server at 20.20.10.5. The initial request timed out but on the second try, I received a successful reply.
The Three-Tier Network provided me the opportunity to apply the skills acquired from the CCNA and grasp the essentials of how a large enterprise structures its network by using a Core layer that is connected to individual blocks. Additionally, I was able to learn about the Collapsed Core Two-Tier Network design commonly used by smaller organisations for a cheaper option in comparison to the Three-Tier Network.
