Semester 3—LAN Switching Chapter 2

Objectives  By the end of this chapter we will be able to perform tasks related to: – Various LAN Communication Problems – Full-Duplex transmitting, Fast Ethernet, and LAN Segmentation. – Switching and VLANs – The Spanning Tree Protocol.

Elements of Ethernet Networks  The data frame broadcast delivery nature of Ethernet/802.3 LANs.  Carrier sense multiple access collision detect (CSMA/CD) access methods allowing only one station to transmit at a time.  Multimedia applications with higher bandwidth demand such as video and the Internet, coupled with the broadcast nature of Ethernet, can create network congestion.  Normal latency as the frames travel across the Layer 1 medium and through Layer 1, 2, and 3 networking devices, and the latency added by the extension of Ethernet/802.3 LANs by adding repeaters.  Extending the distances of the Ethernet/802.3 LANs by using Layer 1 repeaters.

Elements of Ethernet  One of the inherent problems with CSMA/CD technology is collisions.  All Devices are connected to same delivery medium.

Half-Duplex Ethernet Operation 1.NIC sends a frame. 2.NIC Loops the sent frame into its receive pair. 3.The hub receives the frame. 4.The hub sends the frame across an internal bus. 5.The hub repeats the signal out to all other devices.

Half Duplex Ethernet  Receive Rx. (Pin 2, 6; orange, green)  Transmit TX. (Pin 1,3; WOrange, WGreen)  Loop Back.  Collision Detection.  Jam Signal.  Backoff Algorithm.

Full-Duplex Ethernet  Frames that are sent can not collide with frames being received; no collisions are possible.  Loop back and collision segments are omitted.  Waiting for others to send their frames is not necessary because there is only one sender for each twisted pair.  There is 10 Mbps in each direction, increasing the available band width.  Requirements: NIC with Full- Duplex capability, Ethernet switch; transmission and receipt of data occurs on separate non- competitive circuits.

Fast Ethernet  Two main features of Fast Ethernet: – Faster speed. – Auto Negotiation  Requirements – Fast switch port – Fast NIC

Ethernet LAN Segmentation CCNA Objectives  Describe LAN segmentation using bridges, switches, and routers.  Describe network congestion problem in Ethernet.  Describe the benefits of network segmentation with bridges, switches and routers.  Describe the advantage of LAN Segmentation

LAN Segmentation Using Bridges  Transparent bridging the process of forwarding frames when appropriate. To accomplish this, transparent bridges perform three key functions:  Learning MAC addresses by examining the source MAC address of each frame received by the bridge.  Deciding when to forward a frame and when to filter a frame, based on the destination MAC address.  Creating a loop-free environment with other bridges using the Spanning-Tree Protocol.

LAN Segmentation Using Bridges

Characterizations of transparent bridge  Broadcast and multicast frames are forwarded by a bridge.  Bridges perform switching of frames using layer 2 headers, and are layer 3 protocol-independent.  Store and forward operation is typical in transparent bridging devices.  The transparent bridge must perform processing on the frame, which also can increase latency(as compared to a single LAN Segment.

LAN Segmentation Using a Switch  An Ethernet Switch uses the same logic as a transparent bridge. However the internal logic of the switch is optimized for performing the basic function of choosing when to forward and when to filter a frame. (Switched Fabric). The basic logic of a LAN switch is as follows: 1. A frame is received. 2. If the destination is a broadcast or multicast, forward on all ports. 3. If the destination is a unicast and the address is not in the address table, forward on all ports. 4. If the destination is a unicast and the address is in the address table, forward the frame out the associated port

LAN Segmentation Using a Switch.

Characteristics of LAN Segmentation Using a Switch 1.The two ARP broadcasts (Steps 1 and 5) are sent out all switch ports because switches and bridges do not perform the broadcast fire wall function. 2.After the switching table is built, the switch forwards unicasts only out of the appropriate ports. 3.The switch network has created three separate Ethernet segments. Each segment is called a collision domain.

Collision Domains-Bridges VS. Switches A collision domain is a set of interface cards (NICs) for which a frame sent by one NIC could result in a collision with a frame sent by any other NIC in the collision domain.

Switch Internal Processing

LAN Segmentation Using a Router The ARP broadcasts are not forwarded by the router. Communicating with a different segment will result on saving one MAC address on the clients ARP table: The router’s

Broadcast Domains A broadcast domain is a set of NICs for which a broadcast frame sent by one NIC will be received by all other NICs in the broadcast domain.

Comparison of Segmentation Option