SWITCHED NETWORKSLAN SWITCHING – SWITCHES

Pristina, November 2015

Lecturer: Fleurat GovoriCompTIA A+

CONTENT• Converged network • “Hubbed” network• Switched network• Types of Switches• Switch procedures (Boot sequence, bootloader and LED indicators)• Hierarchy in the Switched Network (Core, Distribution and Access)• MAC Address Table• Symmetric and Asymmetric switching• Frame Forwarding Methods• Memory buffering on switches • Multilayer Switch

INTRODUCTION

• A switched network is a computer network which uses only network switches rather than network hubs on Ethernet local area networks. The switches allow for a dedicated connection to each workstation. A switch allows for many conversations to occur simultaneously.

CONVERGED NETWORK • Converged network deliver voice, video streams, text and

graphics between many different types of devices over the same communication channel and network structure.

“HUBBED” NETWORK

• Advantages- Cheap

• Disadvantages - Everything

SWITCHED NETWORK• A switched LAN allows more flexibility, traffic management,

and additional features, such as:• Quality of service• Additional security• Support for wireless networking and connectivity• Support for new technologies, such as IP telephony and mobility

servicesDisadvantages- More expensive

HUBS VS SWITCHES

HUBS VS SWITCHESHub Switch

Layer Layer 1 devices of the OSI model.

Layer 2 of the OSI model.

Ports 4/12 ports 24/48 portsDevice Type Passive Device (Without

Software)Active Device (With Software)

Data transmission

Electrical signal or bits Frame (L2 Switch) & Packet (L3 switch)

Security No privacy More secureTable Cannot learn or store MAC

addresses.MAC address table is key factor in Switches

Transmission Mode

Half duplex Half/Full duplex

Broadcast Domain

Hub has one Broadcast Domain.

Switch has one broadcast domain [unless VLAN implemented]

Collisions Yes (Half-duplex) No (Full-duplex)

TYPES OF SWITCHES• Fixed Configuration Switches

- Features and options are limited to those that originally come with the switch.

• Modular Configuration Switches- The chassis accepts line cards that contain the ports

• Stackable Configuration Switches- Stackable switches, connected by a special cable, effectively operate as one large switch.

FIXED CONFIGURATION SWITCHES

MODULAR CONFIGURATION SWITCHES

STACKABLE CONFIGURATION SWITCHES

SWITCH BOOT SEQUENCE

1. Power-on self test (POST).2. Run boot loader software. 3. Boot loader performs low-level CPU initialization. 4. Boot loader initializes the flash file system 5. Boot loader locates and loads a default IOS operating

system software image into memory and passes control of the switch over to the IOS. 

SWITCH LED INDICATORS

• Each port on switches have status LED indicator lights. • The following modes are available on switches:

- System LED - Redundant Power System (RPS) LED - Port Status LED - Port Duplex LED - Port Speed LED - Power over Ethernet (PoE) Mode LED Presentation

ACCESSING BOOTLOADER(RECOVERING FROM A SYSTEM CRASH)• The boot loader can also be used to manage the switch if the IOS

cannot be loaded.• The boot loader can be accessed through a console connection by:

1. Connecting a PC by console cable to the switch console port.Unplug the switch power cord.2. Reconnecting the power cord to the switch and press and hold the Mode

button.3. The System LED turns briefly amber and then solid green.Release the Mode button.And the boot loader is loaded.

CONSOLE CONNECTION

HIERARCHY IN THE SWITCHED NETWORK

• Core Layer- The core layer is the network backbone.

• Distribution Layer- The distribution layer interfaces between the access layer and the core layer to provide many important functions

• Access Layer- The primary function of an access layer switch is to provide network access to the user.

CORE DISTRIBUTION ACCESS

HIERARCHICAL NETWORKS

MAC ADDRESS TABLE• Switches use MAC addresses to direct network

communications through the switch to the appropriate port toward the destination. 

Step 1: The switch receives a frame from PC1 on Port 1

Step 2: The switch examines the source MAC address and compares it to MAC address table.

Step 3: After the switch has recorded the source address information, the switch examines the destination MAC address and generates an ARP request (if MAC isn’t present in Table)

Step 4: The destination device (PC3) replies to the frame with a unicast frame addressed to PC1

• Step 5: The switch enters the source MAC address of PC3 and the port number of the ingress port into the address table. The destination address of the frame and its associated egress port is found in the MAC address table

Step 6: The switch can now forward frames between these source and destination devices without flooding, because it has entries in the address table that identify the associated ports

SYMMETRIC AND ASYMMETRIC SWITCHING

• Symmetric switching • Asymmetric switching

Note: Most switches are now 10/100/1000, which allow you to use them symmetrically or asymmetrically.

FRAME FORWARDING METHODS ON SWITCHES• Switches use one of the following forwarding methods for

switching data between network ports:- Store-and-forward switching

- A store-and-forward switch receives the entire frame, and computes the CRC. If the CRC is valid, the switch looks up the destination address, which determines the outgoing interface. The frame is then forwarded out the correct port.

- Cut-through switching- Forwards the frame before it is entirely received. At a minimum, the

destination address of the frame must be read before the frame can be forwarded.

STORE-AND-FORWARD SWITCHING

CUT-THROUGH SWITCHING

MEMORY BUFFERING ON SWITCHES

• Port-based Memory Buffering- Frames are stored in queues that are linked to specific

incoming and outgoing ports.• Shared Memory Buffering

- deposits all frames into a common memory buffer that all the ports on the switch share.

• Shared Memory Buffering • Port-based Memory Buffering

MULTILAYER SWITCH (MLS)

SUMMARY

In this presentation you learned:• Hub vs Switch network• Switch procedures (Boot sequence, bootloader and LED

indicators)• MAC Address Table• Symmetric and Asymmetric switching• Frame Forwarding Methods• Memory buffering on switches • Multilayer Switch

REFERENCES

• http://www.diffen.com• http://www.netacad.com• http://moodle.ubt-uni.net/

QUESTIONS?