Chapter 4 – Sections & Objectives
- 4.1 LAN Design
- Explain how switched networks support small to medium-sized businesses.
- Explain how data, voice, and video are converged in a switched network.
- Describe a switched network in a small to medium-sized business.
- 4.2 The Switched Environment
- Explain how Layer 2 switches forward data in a small to medium-sized LAN.
- Explain how frames are forwarded in a switched network.
- Compare a collision domain to a broadcast domain.
4.1 LAN Design
4.1.1 Converged Networks
Growing Complexity of Networks
- Our digital world is changing.
- Information must be accessed from anywhere in the world.
Elements of a Converged Network
- To support collaboration, networks employ converged solutions.
- Data services include voice systems, IP phones, voice gateways, video support, and video conferencing.
- Call control, voice messaging, mobility, and automated attendant are also common features.
- Multiple types of traffic; only one network to manage.
- Substantial savings over installation and management of separate voice, video, and data networks.
- Integrates IT management.
Cisco Borderless Networks
- A network architecture that allows organizations to connect anyone, anywhere, anytime, and on any device securely, reliably, and seamlessly.
- Designed to address IT and business challenges, such as supporting the converged network and changing work patterns.
Hierarchy in the Borderless Switched Network
- Borderless switched network design guidelines are built upon the following principles:
Access, Distribution, and Core Layers
4.1.2 Switched Networks
Role of Switched Networks
- Switching technologies are crucial to network design.
- Switching allows traffic to be sent only where it is needed in most cases, using fast methods.
- A switched LAN:
- Allows more flexibility
- Allows more traffic management
- Supports quality of service, additional security, wireless, IP telephony, and mobility services
4.2 The Switched Environment
4.2.1 Frame Forwarding
Switching as a General Concept in Networking and Telecommunications
- A switch makes a decision based on ingress and a destination port.
- A LAN switch keeps a table that it uses to determine how to forward traffic through the switch.
- Cisco LAN switches forward Ethernet frames based on the destination MAC address of the frames.
Dynamically Populating a Switch MAC Address Table
- A switch must first learn which devices exist on each port before it can transmit a frame.
- As a switch learns the relationship of ports to devices, it builds a table called a MAC address or content addressable memory (CAM) table.
- CAM is a special type of memory used in high-speed searching applications.
- The information in the MAC address table is used to send frames.
- When a switch receives an incoming frame with a MAC address that is not found in the CAM table, it floods it to all ports, except the one that received the frame.
Switch Forwarding Methods
- Allows the switch to:
- Check for errors (via FCS check)
- Perform automatic buffering
- Slower forwarding process
- Allows the switch to start forwarding in about 10 microseconds
- No FCS check
- No automatic buffering
4.2.2 Switching Domains
- Collision domain – Segment where devices compete to communicate.
- Ethernet switch port:
- Operating in half duplex, each segment is in its own collision domain.
- Operating in full duplex eliminates collisions.
- By default, will auto-negotiate full duplex when the adjacent device can also operate in full duplex.
- A broadcast domain is the extent of the network where a broadcast frame can be heard.
- Switches forward broadcast frames to all ports; therefore, switches do not break broadcast domains.
- All ports of a switch, with its default configuration, belong to the same broadcast domain.
- If two or more switches are connected, broadcasts are forwarded to all ports of all switches, except for the port that originally received the broadcast.
Alleviating Network Congestion
- Switches help alleviate network congestion by:
- Facilitating the segmentation of a LAN into separate collision domains.
- Providing full-duplex communication between devices.
- Taking advantage of their high-port density.
- Buffering large frames.
- Employing high-speed ports.
- Taking advantage of their fast internal switching process.
- Having a low, per-port cost.
4.3 Chapter Summary
The trend in networks is towards convergence using a single set of wires and devices to handle voice, video, and data transmission.
There has been a dramatic shift in the way businesses operate.
There are no physical offices or geographic boundaries constraints. Resources must now be seamlessly available anytime and anywhere.
The Cisco Borderless Network architecture enables different elements, from access switches to wireless access points, to work together and allow users to access resources from any place, at any time.
The traditional, three-layer hierarchical design model divides the network into core, distribution, and access layers, and allows each portion of the network to be optimized for specific functionality.
It provides modularity, resiliency, and flexibility, which provides a foundation that allows network designers to overlay security, mobility, and unified communication features.
Switches use either store-and-forward or cut-through switching.
Every port on a switch forms a separate collision domain allowing for extremely high-speed, full-duplex communication.
Switch ports do not block broadcasts and connecting switches can extend the size of the broadcast domain, often resulting in degraded network performance.
Terms and Commands
- Converged network
- Cisco borderless networks
- Core layer
- Distribution layer
- Fixed configuration switches
- Modular configuration switches
- Stackable configuration switches
- Cost of a switch
- Frame buffers
Terms and Commands
- Ingress port
- Content addressable memory (CAM)
- Cut-through switching
- Store-and-forward switching
- Frame-check-sequence (FCS)
- Fragment free switching
- Collision domain
- Broadcast domain
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