Chapter 9 Ethernet – Part 1

1. Chapter 9Ethernet – Part 1

2. Ethernet Fundamentals Part 1 • Introduction to Ethernet Part 2 • Layer 2 and Ethernet Switches • Cables, Duplex, and Troubleshooting • Ethernet and the OSI Model – more detail • Ethernet frames – more detail

3. Introduction to Ethernet

4. Ethernet Local Area Networks (LANs) • LAN (Local Area Network) - A computer network connected through a wired or wireless medium by networking devices (hubs, switches, routers) and administered by a single organization. • Ethernet – A family of Layer 2 Data Link protocols for Local Area Networks .

5. IEEE Standards Brief History: • 1970’s - Robert Metcalfe and his coworkers at Xerox PARC • 1980 - Ethernet protocol published by Digital Equipment Corporation, Intel, and Xerox (DIX) • 1985 - Institute of Electrical and Electronics Engineers (IEEE) published IEEE 802.2 and 802.3

6. Data Link Sublayers IEEE 802 Extension to the OSI Model LLC (Logical Link Control) MAC (Media Access Control) • The Institute of Electrical and Electronic Engineers (IEEE) is a professional organization that defines network standards. • IEEE 802.3 “Ethernet” is the predominant and best known LAN standards, along with 802.11 (WLAN). • The IEEE divides the OSI data link layer into two separate sublayers. Recognized IEEE sublayers are: • Media Access Control (MAC) (transitions down to media) • Logical Link Control (LLC) (transitions up to the network layer)

7. LLC – Logical Link Sublayer • Logical Link Control (LLC)defined in the IEEE 802.2 specification • Provides versatility in services to network layer protocols that are above it, while communicating effectively with the variety of technologies below it. • The LLC, as a sublayer, participates in the encapsulation process.

8. 802.2 LLC * * IPX IP APPLE-TALK Layer 3 LLC Layer 2 - LLC * * Ethernet Token Ring FDDI MAC &Layer 1 * Legacy technologies

9. 802.2 LLC Data Encapsulation Example Application Header + data Application Layer Layer 4: Transport Layer Layer 3: Network Layer Layer 2: Data Link Layer 010010100100100100111010010001101000… Layer 1: Physical Layer We have been focusing on the Layer 2, Data Link, Ethernet Frame for now.

10. MAC – Media Access Control Sublayer • The Media Access Control (MAC) sublayer deals with the protocols that a host follows in order to access the physical media. • Defined in IEEE 802.3 specification • Responsible for the actual framing • Builds the 1s and 0s to hand off to the physical layer. • Responsible for media access (CSMA/CD)

11. The IEEE Working Groups 802.1 Networking Overview and Architecture 802.2 Logical Link Control Ethernet 802.3 802.4 Token Bus 802.5 Token Ring 802.6 MANs 802.7 Broadband 802.8 Fiber Optic 802.9 Isochronous LAN 802.11 Wireless LAN ...and more!

12. Network Interface Card (NIC)

13. Network Interface Card (NIC) Network Interface Card (NIC) • Layer 2, Data Link Layer, device • Connects the device (computer) to the LAN • Responsible for the local Layer 2 address (later) • Common Layer 2 NICs: • Ethernet • Token Ring • Common Bandwidth • 10 Mbps, 10/100 Mbps, 10/100/1000 Mbps

14. Tracing the Physical Connection NIC (Network Interface Card)

15. Connecting the NIC to a Hub or Switch…

16. From PC to Ethernet Port…

17. From Ethernet Port to Patch Panel… Back View Front View

18. From Patch Panel to Switch (or hub)

19. From PC to Switch

20. All of that is the same as these!

21. Our focus! • Ethernet protocol is only concerned with how the information gets from one Ethernet host or device to another.

22. Ethernet and IEEE 802.3 • This standard includes the protocol used to “frame” the data by the sending Ethernet host computer. • Most of the time, the term “Ethernet” is used to mean IEEE 802.3 • Ethernet and IEEE 802.3 are used interchangeably, even though they are not really the same thing. (more later)

23. Ethernet “Data” Data may be: • IP Packet • ARP Message • Other

24. The MAC Address • Part of the Ethernet protocol includes the MAC (Media Access Control) • Every Ethernet NIC card has a unique MAC address. • MAC addresses provide a way for computers to identify themselves. • They give hosts a permanent, unique name.

25. The MAC Address • MAC addresses are: • 48 bits in length • Expressed as 12 hexadecimal digits. • The first 6 hexadecimal digits, which are administered by the IEEE, identify the manufacturer or vendor and thus comprise the Organizational Unique Identifier (OUI). • The remaining 6 hexadecimal digits comprise the interface serial number, or another value administered by the specific vendor. • MAC addresses are sometimes referred to as burned-in addresses (BIAs) because they are burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes

26. The MAC Address • The Ethernet protocol uses MAC addresses to identify the source of the Ethernet frame and the destination of the Ethernet frame. • Whenever is computer sends an Ethernet frame, it includes the MAC address on its NIC as the Source “MAC” Address. • We will learn later how it learns the Destination “MAC” Address. • We will see how all of this works in a moment. MAC Address MAC Address

27. 0000 = 0 1000 = 8 0001 = 1 1001 = 9 0010 = 2 1010 = A 0011 = 3 1011 = B 0100 = 4 1100 = C 0101 = 5 1101 = D 0110 = 6 1110 = E 0111 = 7 1111 = F Decimal, Binary, Hex DecBinHexDecBinHex 0 = 0000 = 0 8 = 1000 = 8 1 = 0001 = 1 9 = 1001 = 9 2 = 0010 = 2 10 = 1010 = A 3 = 0011 = 3 11 = 1011 = B 4 = 0100 = 4 12 = 1100 = C 5 = 0101 = 5 13 = 1101 = D 6 = 0110 = 6 14 = 1110 = E 7 = 0111 = 7 15 = 1111 = F

28. MAC Address Format OUIunique • An Intel MAC address: 00-20-E0-6B-17-62 • 0000 0000 - 0010 0000 – 1110 0000 - 0110 1011 – 0001 0111 – 0110 0010 • IEEE OUI FAQs: http://standards.ieee.org/faqs/OUI.html DecBinHexDecBinHex 0 = 0000 = 0 8 = 1000 = 8 1 = 0001 = 1 9 = 1001 = 9 2 = 0010 = 2 10 = 1010 = A 3 = 0011 = 3 11 = 1011 = B 4 = 0100 = 4 12 = 1100 = C 5 = 0101 = 5 13 = 1101 = D 6 = 0110 = 6 14 = 1110 = E 7 = 0111 = 7 15 = 1111 = F

29. What is the Address on my NIC?

30. MAC Addresses Are Flat • MAC addresses provide a way for computers to identify themselves. • They give hosts a permanent, unique name. • The number of possible MAC addresses is 16^12 (or over 2 trillion!). • MAC addresses do have one major disadvantage: • They have no structure, and is considered flat address space. • Like using just a name when sending a letter instead of a structured address.

31. Generic Data Link Frame • A message is “framed” (layer 2) and transmitted on the cable (layer 1) by the Ethernet NIC. • Framing provides order, or structure, to the stream of bits, bitstream.

32. Bringing it all together… • Let’s pause here for a moment and figure all of this out! • Let’s bring the following together: • Ethernet Frames and MAC Addresses • Sending and receiving Ethernet frames on a bus • CSMA/CD • Sending and receiving Ethernet frames via a hub • Sending and receiving Ethernet frames via a switch

33. Serial vs Multiaccess Network Serial Multiaccess

35. Ethernet: Multiaccess Network

36. Bus Topology A bus topology uses a single backbone segment (length of cable) that all the hosts connect to directly. Original Ethernet used a bus topology. By the way, Ethernet hubs work the same as a “bus”.

37. Sending and receiving Ethernet frames on a bus Abbreviated MAC Addresses 1111 2222 3333 nnnn • When an Ethernet frame is sent out on the “bus” all devices on the bus receive it. • What do they do with it? 3333 1111

38. Sending and receiving Ethernet frames on a bus Hey, that’s me! Nope Nope Abbreviated MAC Addresses 1111 2222 3333 nnnn • When information (frame) is transmitted, every PC/NIC on the shared media copies part of the transmitted frame to see if the destination address matches the address of the NIC. • If there is a match, the rest of the frame is copied • If there is NOT a match the rest of the frame is ignored. • Unless you are running a protocol analyzer program such as Ethereal. 3333 1111

39. Sending and receiving Ethernet frames on a bus • So, what happens when multiple computers try to transmit at the same time? Abbreviated MAC Addresses 1111 2222 3333 nnnn

40. Sending and receiving Ethernet frames on a bus Collision! Abbreviated MAC Addresses 1111 2222 3333 nnnn X

41. Access Methods Two common types of access methods for LANs include • Non-Deterministic: Contention methods (Ethernet, IEEE 802.3) • Only one signal can be on a network segment at one time. • Collisions are a normal occurrence on an Ethernet/802.3 LAN • Deterministic: Token Passing (Token Ring) • more later

42. CSMA/CD (Carrier Sense Multiple Access with Collision Detection) CSMA/CD Common contention method used with Ethernet and IEEE 802.3 • “Let everyone have access whenever they want and we will work it out somehow.”

43. CSMA/CD and Collisions CSMA/CD (Carrier Sense Multiple Access with Collision Detection) • Listens to the network’s shared media to see if any other users on “on the line” by trying to sense a neutral electrical signal or carrier. • If no transmission is sensed, then multiple accessallows anyone onto the media without any further permission required. • If two PCs detect a neutral signal and access the shared media at the exact same time, a collision occurs and is detected. • The PCs sense the collision by being unable to deliver the entire frame (coming soon) onto the network. (This is why there are minimum frame lengths along with cable distance and speed limitations. This includes the 5-4-3 rule.) • When a collision occurs, a jamming signal is sent out by the first PC to detect the collision. • Using either a priority or random backoff scheme, the PCs wait certain amount of time before retransmitting. • If collisions continue to occur, the PCs random interval is doubled, lessening the chances of a collision.

44. CSMA/CD and Collisions Hey, that’s me! And as we said, • When information (frame) is transmitted, every PC/NIC on the shared media copies part of the transmitted frame to see if the destination address matches the address of the NIC. • If there is a match, the rest of the frame is copied • If there is NOT a match the rest of the frame is ignored. Nope Nope Abbreviated MAC Addresses 1111 2222 3333 nnnn Notice the location of the DA! 3333 1111

45. Sending and receiving Ethernet frames via a hub Hub or • Only one device on the hub can communicate at a time, otherwise collisions occur. • 10 Mbps ports are the most common. • 100/1000 Mbps also “available”. • The hub acts the same as a “bus”.

46. Sending and receiving Ethernet frames via a hub • So, what does a hub do when it receives information? • A hub is nothing more than a multiport repeater. 3333 1111 1111 ? 2222 5555 3333 4444

47. Repeaters • Signals can only travel so far through media before they weaken, and become garbled. • This weakening of signals is called attenuation. • Attenuation increases when: • Media distances are lengthened • Nodes are added to the media • Repeaters: • take in weakened signals • clean them up • regenerate them • send them on their way along the network

48. Repeater: Layer 1 Device Signal come in … signal go out. (after I amplify it) • Repeaters are Layer 1 devices. • They do NOT look at: • Layer 2, Data Link (MAC, Ethernet) addresses • Layer 3, IP Addresses.

49. Hub • Hub is nothing but a multiport repeater. • Hubs are Layer 1 devices. • Data that comes in one port is sent out all other ports, except for the port it came in on.

50. Hubs • Hubs allow computers and other network devices to communicate with each other, and use a star topology. • Like a repeater, a hub regenerates the signal. • Hubs have the same disadvantage as a repeater, anything it receives on one port, it FLOODS out all other ports. • Wherever possible, hubs should be replace by switches.