Module 5 - Ethernet LAN Switching.1.pptx

Ethernet LAN Switching Module 5 Local Area Networks (LANs) Ethernet Frame Trailer packet Heade r FCS Preambl SFD Destination Sourc Type e e...

Ethernet LAN Switching Module 5 Local Area Networks (LANs) Ethernet Frame Trailer packet Heade r FCS Preambl SFD Destination Sourc Type e e Start Frame (or Frame Check length) Delimiter Sequenc e Preamble and SFD Preambl SFD e Length – 7- byte (56 - Start Frame Delimiter bit) Length – 1 byte ( 8 - Alternating 1’s and 0’s bit) 10101010 * 7 10101011 Allows devices to Marks the end of the synchronize their preamble, and the receiver clocks beginning of the rest of the frame Destination and Source Destination Sourc e Indicate the devices sending and receiving the frame Consist of the destination and source “MAC address MAC – Media Access Control 6 - byte ( 48 – bit) address of the physical device Type or Length Type 2- byte (16 - bit) field A value of 1500 or less in this field indicate the length of the encapsulated packets (in bytes) A value of 1536 or greater in this field indicates the TYPE of the encapsulated packet ( usually IPv4 or IPv6), and the length are determined via another methods IPv4 =0x0800 (hexadecimal) IPv6 = 0x86DD (hexadecimal) ( 2048 in decimal) (34525 in decimal) Frame Check Sequence FCS Frame check Sequence 4- byte (32-bit) in length Detects corrupted data by running a “CRC” algorithm over the received data CRC – Cyclic Redundancy Check sometimes called Cyclic Redundancy Codes Ethernet Frame 4 7 1 6 6 2 = 26 - byte ( header + trailer) this is an overview of each field of an ethernet frame. MAC Address 6 - byte (48 - bit) physical address assigned to the device when it is made Also known as Burned –In Address (BIA) Is globally unique The first 3 bytes are the OUI ( Organizationally Unique Identifier), which is assigned to the company making the device The last 3 bytes are unique to the device itself Written as 12 hexadecimal characters MAC Address Different Format of MAC Address 1. For Windows – 5C-23-5A-24-2B-3D 2. For Cisco devices – 0011.5ccc.5c00 3. For LINUX and IOS - 5C:23:5A:24:2B:3D  Unicast frame : a MAC Address frame destined for single target Destination : PC2 -.0002 Source: PC 1 - 0001 Unknown Unicast Frame =PC2 MAC Address Table of Flood the frame for all Switch MAC Interface interfaces except for the AAAA.AA00.000 Fa0/1 Known sourceUnicast Frame 1 forward AAAA.AA00.000 Fa0/2 2 Dynamic MAC addresses are Dynamically learned MAC removed from the MAC address address or Dynamic MAC table after 5 min of inactivity. Address Ethernet Frame  Preamble and SFD is usually not considered part of the Ethernet  header The size of the Ethernet header and trailer is 6+6+2+4 = 18 bytes  The minimum size for an Ethernet frame ( header + payload(packet) +trailer) is 64 bytes  64 bytes – 18 bytes (header + trailer size) = 46 bytes  The minimum payload(packet) sized is 46 bytes  If the minimum payload(packet) is less than 46 bytes, padding bytes are added. Ethernet LAN Switching ARP (Address Resolution Protocol) Source IP: 192.168.1.1 Destination IP : 192.168.1.3 Source MAC:.0001 Destination MAC: ? ARP ( Address Resolution Protocol)  ARP is used to discover the layer 2 address( MAC address) of a known Layer 3 address (IP address)  Consist of two messages : ARP Request – sent by the device that wants to know the MAC address of the other device ARP Reply – which is sent to inform the requesting device of the MAC address  ARP Request is broadcast – sent to all host on the network.  ARP Reply is Unicast – sent only to one host ( the host that sent the request) ARP Request ARP Request Source IP: 192.168.1.1 SW1 MAC Address Destination IP : 192.168.1.3 SW2 MAC Address Table Source MAC:.0001 Table MAC Interface Destination MAC: MAC Interface.0001 Fa0/3 FFFF.FFFF.FFFF.0001 Fa0/3.0003 Fa0/1.0003 Fa0/1 ARP Table In command prompt typed arp –a to view the ARP table (window, macOS, Linux) Internet address – IP address (layer 3 address) Physical address – MAC address (layer 2 address) Type Static – default entry Type dynamic – learned via ARP Ping  A network utility that is used to test reachability  Measured round-trip time  Uses two messages: ICMP Echo Request and ICMP Echo Reply  Command to use is ping (IP –address) MAC Address Table Clearing the MAC Address Table Clearing the MAC Address Table Clearing the MAC Address Table Switch Interfaces CLI Commands Switch>en Switch#sh ip int br Router interfaces have the shutdown command applied by default – will be in the administratively down/down state by default Switch interfaces do not have the shutdown command applied by default – will be in up/up state if connected to another device or down/down state if not connected to another device. CLI Commands Switch>en Switch#show interface status CLI Commands Cont… Interface Range Cont… Cont…. Full/Half Duplex Half duplex – the device cannot send and receive data at the same time. If it is receiving a frame, it must wait before sending a frame. Devices attached to a hub must operate in half duplex Full duplex – the device can send and receive data at the same time. It does not have to wait. Devices attached to a switch can operate in full duplex CSMA/CD –Carrier Multiple Access with Collision Detection  Before sending frames, devices listen to the collision domain until they detect that the other devices are not sending.  If a collision does occur, the device sends a jamming signal to inform the other devices that a collision happened.  Each device will wait a random period of time before sending frames again.  The process repeats. Speed/Duplex Autonegotiation  Interfaces that can run at different speeds (10/100 or 10/100/1000) have default settings of speed auto and duplex auto.  Interfaces advertise their capabilities to the neighboring device, and they negotiate the best speed and duplex settings they are both capable of. E = 10 megabits per second F = 10/100 megabits per second G = 10/100/1000 gigabits per second Cont… What if autonegotiation is disable on the device connected to the switch? Speed – the switch will try to sense the speed that the other device is operating at. If it fails to sense the speed, it will use the slowest supported speed. Interfaces Errors Runts – frames that are smaller than the maximum frame size (64 bytes) Giants – frames that are larger than the maximum frame size (1518 bytes) CRC – frames that failed the CRC check(in the ethernet FCS Trailer) Frames – frames that have an incorrect format (due to an error) Input errors – total of various counters, such as the above four Output errors - frames the switch tried to send , but failed due to error