LAN DESIGNS

Question 1

Briefly describe three-tier LAN architecture

Answer 1

A packet flows to the core, is routed to the correct distribution switch, then forwarded on to the access switch where the server was connected; moving through only 3 physical hops which limits the amount of latency added per-packet flow.

*See Netacad for illustration

Question 2

What are the challenges associated with three-tier LAN architecture?

Answer 2

• The main challenge with this design for the modern data center is that much more intra-DC traffic is the new norm. Due to server to server traffic, three hops now quickly become four or more, adding significant
latency per flow, as well as adding more possibility for bottlenecks, buffer overruns and dropped packets.
• It also introduced loops, as seen in the graphic, requiring correct spanning-tree protocol (STP) configuration. Spanning-tree failures cause
continuous looping and are notorious for causing network outages.

Question 3

What is STP?

Answer 3

STP is a network protocol that builds a loop-free logical topology for Ethernet networks by preventing bridge loops and the broadcast radiation that results from them

Question 4

What are the three layers of the three-tier architecture?

Answer 4

The Core Layer
Distribution Layer
Access Layer

Question 5

Briefly explain the core layer and outline its primary purpose

Answer 5

The core layer is the network backbone, connecting several layers of the campus blocks together to form the larger campus network.
• The primary purpose of the core layer is to provide fault isolation and high-speed backbone connectivity.

Question 6

What is the recommended topology for the core layer and why?

Answer 6

To build a simplified, scalable, cost-effective, and efficient physical cable layout design, the recommendation is to build an extended-star
physical network topology from a centralized building location to all other buildings on the same campus.

Question 7

Describe core layer switches

Answer 7

Core layer switches are usually large modular chassis with very high throughput and advanced routing capabilities.

Question 8

What are the functions of the distribution layer?

Answer 8

– Aggregating large-scale wiring closet networks
– Aggregating Layer 2 broadcast domains and Layer 3 routing boundaries
– Providing intelligent switching, routing, and network access policy functions to access the rest of the network
– Providing high availability through redundant distribution layer switches to the end-user and equal cost paths to the core
– Providing differentiated services to various classes of service applications at the edge of the network

Question 9

Describe distribution layer switches

Answer 9

Distribution layer switches are mid-tier speed switches with emphasis on uplink speeds. Services, such as load balancing or firewalls, could often be found at this layer.

Question 10

Describe the access layer

Answer 10

The access layer represents the network edge, where traffic enters or exits the campus network. Traditionally, the primary function of an access layer switch is to provide network access to the user

Question 11

Describe access layer switches

Answer 11

Access Layer Switches are the traditional top-of-rack (TOR) switch that regularly consists of 24 to 48 ports of 1 or 10Gbps ports with similarly sized uplinks.
They connect to distribution layer switches, which
implement network foundation technologies such as routing, quality of service, and security.

Question 12

What improvements have been made to the access layer

Answer 12

The next-generation switching platforms now provide more converged, integrated, and intelligent services to various types of endpoints at the network edge.
Building intelligence into access layer switches allows applications to operate on the network more efficiently and securely.

Question 13

What is Top-of-rack switching?

Answer 13

Top-of-rack switching is a network architecture design in which computing equipment like servers, appliances and other switches located within the same or adjacent rack are connected to an in-rack network switch. Despite the name, ToR switches can be placed anywhere in the rack.

Question 14

Describe two-tier architecture

Answer 14

Also known as collapsed core or spine-leaf architecture/folded CLOS*. It solves the problem of the three tier architecture and meets the needs of modern
applications: high-throughput and low-latency.

Question 15

What is latency?

Answer 15

delay before a transfer of data begins following an instruction for its transfer

Question 16

Describe a CLOS network

Answer 16

A kind of multistage circuit-switching network which represents a theoretical idealization of practical, multistage switching systems, named after Charles Clos.

Question 17

In what situation is the two-tier architecture recommended

Answer 17

In some cases where extensive physical or network scalability does not exist and there are fewer users accessing the network or in campus sites consisting of a single building, maintaining separate distribution and core layers is not required.

Question 18

Describe spine switches

Answer 18

Spine Switches are very high-throughput, low-latency and port-dense switches that have direct high-speed (40-300Gbps) connections to each leaf switch.

Question 19

Describe leaf switches

Answer 19

Leaf Switches are very similar to traditional TOR* switches in that they are often 24 or 48 port 1, 10 or 40Gbps access layer connections, but have the increased capability of either 40, 100 or 300Gbps uplinks to each spine switch.

Question 20

What are the advantages of two- tier architecture

Answer 20

• Resiliency: Each leaf switch connects to every spine switch, spanning-tree is not needed and due to TRILL, SPB or SDN protocols, every uplink can be used concurrently.
• Latency: There is a maximum of 2 hops for any East-West packet flows so ultra-low-latency is standard.
• Performance: True active-active uplinks enable traffic to flow over the least congested high-speed links available.
• Scalability: You are able to increase leaf switch quantity to desired port capacity and add spine switches as needed for uplinks.
• Adaptability: Multiple spine-leaf networks across a multicloud ecosystem can be connected and managed from a single pane of glass.
Also, this topology has benefits in other areas of the enterprise network (for example, industrial cell architecture or corporate LAN).

Question 21

What are some more considerations with regards to LAN designs?

Answer 21

To modernize the logic network, it is recommended adding a software-defined network (SDN) platform like Cisco ACI or VMWare NSX.

Question 22

What are some of the hidden costs of two-tier architecture?

Answer 22

• With a Two-Tier architecture, the data center will need to be recabled. Each leaf will need to connect to each spine. This new design requires a considerable amount of cable as well as optics for connectivity.
• Two-Tier, spine-leaf architectures may still require core switches for layer three routing. Planning both the physical and logical network is critical before purchasing the hardware for a new data center.