When networks are connected linearly (aka daisy chained), they can cause spanning tree loops and have single points of failure that can sever connections and take down the entire network. Networks should be structured in a way that minimizes these failures.
Two Tier Architecture aka Distribution Model
The two tier model is the best way to start building an enterprise network.
Distribution Switch. This is the switch which will only be connected to critical equipment such as the routers, administration servers and the access switches. Core switches should come in redundant pairs, connected together, connected to the access switches and powered separately. This ensures redundancy and prevents critical network failures. Core / Distribution switches are the level at which VLANS, routing, access control lists and quality of server are managed.
Access Switches. All other equipment is connected to the access switches such as workstations, local WAPs and printers.
Collapsed core can be scaled up to support thousands of employees but is simple enough to work as a basic starting point for a small business network. It is very common for first iteration networks to daisy chain switches which is a mistake due to their potential for critical network outages. When implementing a new network go with the distribution aka collapsed core model.
Three Tier Architecture aka Campus Network
As a two tier network grows, more and more distribution switches are added and the cross connections increase. By adding a new tier on top, you can aggregate the distribution tier and manage cross connections more efficiently.
Core switches. The switches that aggregate the distribution switches together. Fast connection point for efficient data transfer.
Spine and Leaf Architecture
Spine and leaf is a design meant to be implemented in datacenters and server rooms. The best architecture for east-west traffic flows. North-south flow is typified by the two and three tier networks where network traffic flows from computers up through the access and core switches and to the routers toward the internet. East-west flow is when computer hosts on a network communicate with each other.
Server rooms have rows of racks to house servers. In a spine and leaf architecture each rack has a TOR (top of rack) switch. An access level network would just be a few racks networked to the internet. A distribution level network would see the increase in access level racks and have them cross connected to distribution network racks. When the enterprise expands to multiple datacenters, you would add the core level, connecting the distribution level.
“Spine” refers to the network backbone, which are connected to each rack “leaves” (TOR). Each server connects to the rack “leaf”. Cross connections everywhere, there is a full network mesh between spine and leaf. This allows for fast east-west traffic flow, and for combining traffic.
The spine switches are not directly connected together. They are connected through the leaf switches. All spine switched connect to all leaf switches. Leaf switches are only ever one hop away from each other. Every time another spine connection is added, a routed link is added. This means a switch can utilize more than one connection at once. This eliminates bottlenecks.
Wide Area Networks
WANs connect businesses through private connections. Technically the Internet itself is a WAN though its not private. The advantage of having a dedicated private WAN is quality of service which is something the Internet doesn’t guarantee. When a data packet is being sent from one site to another the service provider guarantees it will get there with minimal packet loss and specific times.
There are two primary types of enterprise WAN connections, Leased Line and Packet switched network connections. Dial up modems are another type of WAN connection but are so low bandwidth that it is only used in emergencies when everything else is down.
Leased lines are direct private connections between businesses. They are dedicated single user connections, all the bandwidth is yours to use and when its not is service there is no traffic. T1 lines or E1 lines are Leased Line connections. A disadvantage of Leased Lines is it’s 1:1, 1 site to 1 site and doesn’t scale well when you have multiple locations. They can also be expensive.
MPLS or METROE (Multi Protocol Label Switching or Metropolitan Ethernet) are more commonly used than Leased Lines. They are Packet Switched networks. The carrier uses their own network to distribute our traffic to the sites we need. They use virtual circuits to direct traffic. This is cheaper than dedicated Leased Lines. MetroE is a massive bundle of fiber optics installed underground that connects a metropolitan area together. More fiber is put in the ground at time of installation with the anticipation that demand will grow and can be accommodated without ripping up the street again to install more fiber.
Small Office / Home Office
SOHO is increasingly sought after by companies because it allows their employees to work from home and save the company from spending on work space. There’s no specific model of SOHO and can vary greatly depending on requirements.
The SOHO will have one or more routers connected to either the internal service or to a PSTN or MPLS. If the router may connect to a switch with a WAP connection, or the router may function as a WAP. WAPs can either be cloud based or there can be a controller. Host computers can daisy chain to the switch through POE Cisco phones. A company maybe have a standardized template for what the require of employees WFH SOHO set ups.
On Premise vs Cloud vs Hybrid
Today companies utilize a variety of cloud services to access resources. They use public cloud but may also have their own private cloud or a hybrid cloud. Most businesses use a mix of resource locations.
Public cloud examples: AWS, Azure, Office 365, Google Apps, IBM Cloud. On premises cloud examples, Active Directory Server, Print server. Private cloud: private corporate datacenter or datacenter of datacenter colocation where resources are kept.
Sources:
Cisco Certified Network Associate (200-301 CCNA) Online Training
https://www.cbtnuggets.com/it-training/cisco/ccna
Jeremy Cioara, Keith Barker, Chuck Keith, Knox Hutchinson
Computer Networking Course – Network Engineering [CompTIA Network+ Exam Prep]
https://www.youtube.com/watch?v=qiQR5rTSshw
Brian Ferrel
CCNA Certification Study Guide, Volume 2: Exam 200-301
Todd Lammle
Netstream 360 