Scalability
As any organization grows over time, the necessity of adding new devices or requirements also increases. Cisco's 3-layer hierarchical model allows us to create independent but connected modules. Each has specific functions that help growth without affecting other areas. The following image shows the three-layer model applied in the project.
To ensure orderly growth, I standardized the naming convention for equipment to X-00-YY00. Where X is the building, followed by the first numbers that show the floor. Next is YY, the function of the device. Then, the last numbers show the quantity. For example, if Building B needs a new switch (Access Layer) on the second floor. It would connect to the distribution switches and label it as B-02-SW03, which makes expansion easier. It won't impact other areas and allows for quick location of the device if it fails.
Insolation is another fantastic benefit of the hierarchy model. For example, A loop issue between switches in Building B wouldn't affect equipment in other areas. The distribution layer keeps each block separate. It separates broadcast domains because the connection to the core layer is L3, and to the access layer is L2.
The growth of devices also impacts IP addressing, especially in IPv4. For example, the administration office will get 20 new computers. They will need IP addresses to connect to the internet. This reason led to the selection of (CIDR) blocks. They also make management simple, allowing for flexible assignment of the host part. It also makes scaling easy as needs grow.
Both on and off-campus use the 10.0.0.0/8 block for end-user addressing. Building B's 10.0.0.0/16 block has 16 networks, eight subnet bits, and eight host bits. Creating 255 networks in total that can accommodate 254 clients. For buildings off campus and connecting via VPN, they used 10.1.100.0/16 addressing. They used the same 16/8/8 approach, allowing for significant growth. For example, a new office in location XXX connects via VPN to campus services. It could use the 10.1.101.0/16 addressing, and so on.
OSPF in area 0 uses the 192.168.0.0/32 network addressing, and in area 1, the 172.22.32.0/32 addressing. Here is a practical addressing scheme example. The distribution switches B-00-SW01 and B-00-SW02 announce a summarized route via OSPF that includes all user networks. The core switches learn it as one route. This allows us to create networks from 10.0.0.hhh to 10.0.255.hhh in Building B without modifying OSPF. The table below shows the B-00-SW01 summarization. It also shows the learned route on core switch A-00-SW01.
B-00-SW01#show running-config | section ospf
router ospf 109
—----- texto omitido —--------
area 2 range 10.0.0.0 255.255.0.0
A-00-SW01#show ip route ospf
Codes: IA - OSPF inter area
—----- texto omitido —--------
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O IA 10.0.0.0/16 [110/20] via 192.168.0.18, 00:08:43, GigabitEthernet1/0
Click here to access a detailed sheet of IP addressing by VLAN and by device in the network. It provides an in-depth and clear view of how IP addresses and names are assigned in the network.