Exploring the network

Exploring the network

ETHERNET Chapter 5 Intro to Routing & Switching OBJECTIVES Upon completion of this chapter, you should be able to: Describe the operation of the Ethernet sublayers. Identify the major fields of the Ethernet frame. Describe the purpose and characteristics of the

Ethernet MAC address. Describe the purpose of ARP. Explain how ARP requests impact network and host performance. Explain basic switching concepts. Compare fixed configuration and modular switches. Configure a Layer 3 switch. 5.1.1 ETHERNET OPERATION

ETHERNET OPERATION Most widely used LAN technology What 2 layers does it operate at? Data link & physical

What are the 2 sublayers of the data link? LLC & MAC LLC IEEE 802.2 Helps communicate with network layer

Adds control info Performs it in software MAC SUBLAYER Encapsulates the data Adds MAC addresses Adds error detection to frame Media Access Control

Placing the frames on the media Ethernet is a logical bus; physical star Signal passes to all Can send whenever Can be collisions CSMA

Ethernet is contention-based/non-deterministic Data contends or shares for a spot on the media Doesnt know when itll get access to it Listens for signal on media No signal = transmit data Transmit at same time= collision

Devices do not keep track of whose turn it is More collisions= less throughput SOLUTION: CSMA/CD & CSMA/CA CSMA/CD ON ETHERNET NETWORK

Listens for silence Silence= transmit data If devices transmit at same time, collision Backoff random time, listen for silence, retransmit

Collision detection not a problem much anymore Using switches & full-duplex, this is not a problem anymore CURRENT SWITCHED NETWORK CSMA/CA

Wireless Listen for silence Sends Ready to Send message to AP Gets a Clear to Send message from AP Sends data

MAC ADDRESSES Used to identify frame Each host has a unique address Burned into NIC hardware

48-bits / 12 hex digits / 6 bytes 1st 24 bits OUI; 2nd 24 bits serial # FORWARDING FRAMES ACTIVITY REVIEW How many bits is a MAC address? 48

bits What is the OUI in this MAC? A2:07:CC:F6:AD:32 A2:07:CC What does a wireless network use to avoid collisions? CSMA/CA

What sublayer places the frames on the media? MAC REVIEW The OUI is how many bytes? 3 Ethernet shares access to the media. It

contends for the media and does not take turns transmitting. Not taking turns means the network is Nondeterministic Is the MAC address found in hardware or software? Software End of Day One 5.1.2

ABOUT THE ETHERNET FRAMES FRAME SIZE Min. frame size is 64 bytes; max is 1522 bytes Data is 46-1500 bytes

> 64 bytes is considered a collision ACTIVITY REVIEW What important addresses are encapsulated into a frame? Source

& destination MAC What does the preamble used for? Timing/synchronization What is the minimum frame size? 64 bytes

What happens if a frame is less than 64 bytes? Considered a fragment & dropped REVIEW How many bits in a MAC address? 48

bits How many hex digits? 12 The first 6 hex digits are what? The OUI

The OUI would then be the 1st ____ bytes. 3 What sublayer is used to communicate with the upper layers? LLC 5.1.3 ETHERNET MAC

BINARY/DECIMAL CONVERSION IP Address: 32 bits, 4 octets 8 bits in each octet 11111111.10101010.11001100.00100101 Written in decimal Value in each octet from 0-255 Thats a total of 256 numbers. BINARY/DECIMAL CONVERSIONS Add up the values of the binary 1s

128 64 32 16 8 4 2

1 1 0 0 1 1 1

0 0 156 11100101 229 MAC ADDRESSING

Ipconfig /all Hexadecimal (Base 16) 0-9, A-F (10-15) 16 total #s BINARY/DEC/HEX CONVERSIONS CONVERSION PRACTICE

Handouts HOW MAC ADDRESSES ARE SHOWN Begin with a 0x 0xA4 UNICAST MAC ADDRESS One to one communication

BROADCAST MAC ADDRESS One to all in a network Dest. MAC address will be all Fs DHCP & ARP use broadcasts MULTICAST MAC ADDRESS

One to a group in a network Remote gaming or video conference Dest. IP will be Dest. MAC will begin with 01-00-5E LAB

REVIEW What kind of message gets sent from one PC to a group within a network? Multicast Identify each as unicast, multicast, or broadcast: 5.1.4

MAC & IP MAC & IP MAC address Burned into NIC (DOES NOT CHANGE) Similar to the name of a person Physical address IP address Similar to the address of a person

Based on where the host is actually located Logical address Both the physical MAC & logical IP addresses are required for a computer to communicate just like both the name and address of a person are required to send a letter MAC & IP- TO OTHER NETWORKS

Destination IP NEVER changes! Source & Destination MAC changes at each router interface LAB Wireshark REVIEW How do you change your MAC address?

Get a new NIC T or F. The destination IP address changes during transmission. False What happens to the source & destination MAC addresses as you go

from router to router across the Internet? They change (router port substituted) REVIEW What is IEEE 802.2? LLC

sublayer What is IEEE 802.3? Ethernet/MAC What is a layer 2 address? MAC sublayer

address What is a layer 3 address? IP address 5.2.1 ARP HOW ARP WORKS

ARP table of IP/MACs Added from communication Added from ARP requests You have the dest. IP, not the MAC ARP request is all Fs where? Destination

MAC How is an ARP request sent? Broadcast Who replies to the ARP request? Only one with matching dest. IP HOW ARP WORKS- LOCAL


show ip arp REVIEW If you want to access a remote server, and you dont have the destination MAC, what gets substituted for it? The default gateways MAC address

A router has ports with MAC addresses. How do you view the routers ARP table? Router#sh ip arp What does ARP find? What do you know? Finds the dest. MAC; you know the dest. IP

5.2.2 ARP ISSUES PROBLEMS WITH ARP Broadcasts Its a broadcast. If many devices started at same time, thered be a flood of ARP requests which would cause a reduction in performance for a short period of time.

Security ARP poisoning (or spoofing) Attacker forges MAC address to have frames delivered to different computer Solution: Use a switch USING A SWITCH

Segments network into smaller collision domains Replies go to one device only Implement security too 5.3.1 SWITCHING

HOW A SWITCH WORKS BUILDING A SWITCH TABLE SWITCH DUPLEX SETTINGS Full duplex, Half duplex, Auto Must match setting of device Half duplex uses CSMA/CD to avoid

collisions WHAT CABLE SHOULD IT BE? FORWARDING THE MESSAGE Cisco uses cut-through switching As soon as destination MAC is read, it forwards the frame

Fast-forward Lowest latency; in and out Fragment-free Store first 64 bytes before forwarding Most errors & collision happen there (runts) If it makes it through, should be error-free

ACTIVITY ACTIVITY Complete WHAT WILL HAPPEN? REVIEW 2 switches connect to each other. One port

is 100Mbps and the other is 1000Mbps. What speed will that connection operate at? 100Mbps What feature will allow you to use a straight-through cable to connect two switches together? Auto-MDIX Your switch port is connected to a hub with

3 computers on it. How many MAC addresses will be in the table for that port? 3 ACTIVITY & LAB Switch it! Do it at least 4 times Different scenario each time

Lab together Draw network from MAC address table 5.3.2 TYPES OF CISCO SWITCHES SWITCH FEATURES

Fixed Configuration Switch As is; no add-ons or changing A 24 port switch will always be 24 ports Modular Add-in cards/ports

Stackable Connected by special cable to act as one switch Fixed may be stackable PoE (Power over Ethernet) Delivers power to a device, like an IP phone We use this in school

More $$, faster forwarding rate WHICH IS WHICH? REVIEW Which type of switch can you add a card to add more Ethernet ports or add fiber ports? Modular

You bought a 24 port switch and cannot add more ports to it. What kind of switch did you buy? Fixed You have the switch above and need more ports. You then buy more 24 port switches and connect them with a special cable. What kind of switch do you now have? Fixed & stackable

5.3.3 LAYER 3 SWITCHING LAYER 3 SWITCH Looks like a switch Combined with router functions

Adds in router functions Knows too Fast which IP addresses are out each port ROUTED PORT Make an Ethernet port a routed port To

connect to the ISP Configure a port What have we configured with an IP on a switch? IP for remote management This is similar CONFIGURE ROUTED PORT

/6 F0 LAB Configuring a Layer 3 Switch REVIEW What address(es) does a layer 2 switch read?

MAC What address(es) does a layer 3 switch read? IP addresses & MAC You want to connect your Layer 3 switch to

your ISP instead of using a regular router. What must you configure one of the ports as? Routed port Which command enables the routing function on a switch port? No switchport

REVIEW & STUDY Complete the study guide handout Take the quiz on netacad.com Jeopardy review

SUMMARY In this chapter, you learned: Ethernet is the most widely used LAN technology used today. Ethernet standards define both the Layer 2 protocols and the Layer 1 technologies. The Ethernet frame structure adds headers and trailers around the Layer 3 PDU to encapsulate the message being sent. As an implementation of the IEEE 802.2/3 standards, the Ethernet frame provides MAC addressing and error checking. Using switches in the local network has reduced the probability of frame collisions in half-duplex

links. SUMMARY The Layer 2 addressing provided by Ethernet

supports unicast, multicast, and broadcast communications. Ethernet uses the ARP to determine the MAC addresses of destinations and map them against known IP addresses. Each node on a network has both a MAC address and an IP address. The ARP protocol resolves IPv4 addresses to MAC addresses and maintains a table of mappings. A Layer 2 switch builds a MAC address table that it uses to make forwarding decisions. SUMMARY

Layer 3 switches are also capable of performing Layer 3 routing functions, reducing the need for dedicated routers on a LAN. Layer 3 switches have specialized switching hardware so they can typically route data as quickly as they can switch. ETHERNET Chapter 5

Intro to Routing & Switching

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