Ethernet: A Multi-access Network Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet Protocol Ethernet – Most common LAN technology used today. Multi-access network: Multiple devices on the same medium and able to communicate with each other without the services of a router. Supports data bandwidths of 10 Mb/s, 100 Mb/s, 1 Gb/s, 100 Gb/s, and more Operates in the data link layer and the physical layer. Defined in the IEEE 802.2 and 802.3 standards.

Multi-access Topology A logical multi-access topology - Enables a number of nodes to communicate by using the same shared media. Ethernet LANs – Connected by Ethernet switches (legacy hubs) “Every node “may” see all the frames that are on the medium. Data Link Destination Address denote which device the frame is for.

Bus Topology Original Ethernet used a bus topology. A bus topology uses a single backbone segment (length of cable) that all the hosts connect to directly. Ethernet hubs work the same as a “bus”. And the reason why we have a minimum Ethernet frame size of 64 bytes and specific cable lengths depending upon bandwidth. (See slot time, 5-4-3 rule)

Today’s Ethernet Networks Use Full Duplex NICs and Switches router switch switch switch switch switch switch switch switch Multi-access network: Multiple devices on the same medium and able to communicate with each other without the services of a router.

Ethernet is Best Effort Delivery Ethernet is best-effort delivery, no guarantee. Nothing in the Ethernet frame to ensure delivery. Like a trucking service, it doesn’t really know or care about the what it is carrying.

Ethernet: A Multi-access Network Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet: Ethernet Frame Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet Frame Attributes

Ethernet Frame Attributes Ethernet Frame Size Section 5.1.2.2 Ethernet II and IEEE 802.3 standards define: minimum frame size as 64 bytes maximum as 1518 bytes (1520 with 802.1Q tag) “Collision fragment" or "runt frame” – Frame less than 64 bytes If size of a transmitted frame is less than the minimum or greater than the maximum, the receiving device drops the frame (usually)

Ethernet: Ethernet Frame Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet: Speed (Bandwidth) and Duplex Rick Graziani Cabrillo College graziani@cabrillo.edu

NIC to NIC Ethernet protocol is only concerned with how the information gets from one Ethernet NIC to another. Layer 2, Data Link Layer, device Connects the device (computer) to the LAN Responsible for the local Layer 2 address (later) Default: Full duplex (optional Half duplex) Common Bandwidth 10 Mbps, 10/100 Mbps, 10/100/1000 Mbps

Auto negotiation: Speed and Duplex PC-A Port 1 Autonegotiation Duplex Duplex Full Full Half Half Media Notes: Use graphic in slide. Keep colors consistent. Speed 1000 Mb/s Speed 100 Mb/s 100 Mb/s 10 Mb/s 10 Mb/s

What would be the duplex settings? Half-duplex router Full-duplex switch switch switch hub hub switch switch switch switch Full-duplex

I’m full-duplex so I can send when ever I want. Duplex Mismatch I’m full-duplex so I can send when ever I want. I’m half-duplex so I can only send when the link is clear but I am also getting a lot of collisions! S1 S2 Full-duplex Half-duplex S2 will continually experience collisions because S1 keeps sending frames any time it has something to send. Media Notes: Use graphic in slide.

Ethernet: Speed and Duplex Rick Graziani Cabrillo College graziani@cabrillo.edu

Number Systems: Hexadecimal Rick Graziani Cabrillo College graziani@cabrillo.edu

Rick’s Number System Rules All digits start with 0 A Base-n number system has n number of digits: Decimal: Base-10 has 10 digits Binary: Base-2 has 2 digits Hexadecimal: Base-16 has 16 digits The first column is always the number of 1’s Each of the following columns is n times the previous column (n = Base-n) Base 10: 10,000 1,000 100 10 1 Base 2: 16 8 4 2 1 Base 16: 65,536 4,096 256 16 1

Hexadecimal Digits Dec Hex Dec Hex 0 0 8 8 1 1 9 9 2 2 10 A 3 3 11 B 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 Dec Hex 8 8 9 9 10 A 11 B 12 C 13 D 14 E 15 F Rick Graziani graziani@cabrillo.edu

Hexadecimal Decimal 16’s 1’s 15 F 16 1 0 0, 1, 2, 3, 4, 5, 6, 7 ,8, 9, A, B, C, D, E, F Hexadecimal Decimal 16’s 1’s 15 F 16 1 0

Why Hexadecimal? Hexadecimal is perfect for matching 4 bits. Every combination of 4 bits can be matched with one hex number. 4 bits can be represented by 1 Hex value 8 bits can be represented by 2 Hex values Rick Graziani graziani@cabrillo.edu

Hexadecimal Digits 4 bits can be represented by 1 Hex value Dec Hex Binary 8421 8 8 1000 9 9 1001 10 A 1010 11 B 1011 12 C 1100 13 D 1101 14 E 1110 15 F 1111 Hexadecimal: 16 digits Dec Hex Binary 8421 0 0 0000 1 1 0001 2 2 0010 3 3 0011 4 4 0100 5 5 0101 6 6 0110 7 7 0111

Hexadecimal Digits 4 bits can be represented by 1 Hex value Hexadecimal is perfect for matching 4 bits. Every combination of 4 bits can be matched with one hex number. 4 bits can be represented by 1 Hex value 8 bits can be represented by 2 Hex values Dec. Hex. Binary Dec. Hex. Binary 0 0 0000 8 8 1000 1 1 0001 9 9 1001 2 2 0010 10 A 1010 3 3 0011 11 B 1011 4 4 0100 12 C 1100 5 5 0101 13 D 1101 6 6 0110 14 E 1110 7 7 0111 15 F 1111 Rick Graziani graziani@cabrillo.edu

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

Number Systems: Hexadecimal Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet: MAC Addresses Rick Graziani Cabrillo College graziani@cabrillo.edu

MAC Address: Ethernet Identity Layer 2 Ethernet MAC address is a 48-bit binary value expressed as 12 hexadecimal digits IEEE requires a vendor to follow two simple rules: Must use that vendor's assigned OUI as the first 3 bytes All MAC addresses with the same OUI must be assigned a unique value in the last 3 bytes aka physical address, bia Section 5.1.1.4

MAC Address Format OUI unique An Intel MAC address: 00-21-CC-BA-44-C4 Dec Bin Hex Dec Bin Hex 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 OUI unique An Intel MAC address: 00-21-CC-BA-44-C4 0000 0000 - 0010 0001 – 1100 1100 - 1011 1010 – 0100 0100 – 1100 0100 IEEE OUI FAQs: http://standards.ieee.org/faqs/OUI.html

Ethernet MAC MAC Address Representations Section 5.1.3.2

The MAC Address MAC Address 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…. (ARP)

Ethernet MAC Unicast MAC Address Section 5.1.3.3

Ethernet MAC Broadcast MAC Address Section 5.1.3.4

Ethernet MAC Multicast MAC Address Section 5.1.3.5 Multicast MAC address is a special value that begins with 01-00-5E in hexadecimal Range of IPV4 multicast addresses is 224.0.0.0 to 239.255.255.255

Ethernet: MAC Addresses Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet: Switches and Broadcast Domains Rick Graziani Cabrillo College graziani@cabrillo.edu

Full-duplex Switches Full-duplex is allows simultaneous communication between a pair of stations or devices. 100% bandwidth utilization

Broadcast Domain

Ethernet: Switches and Broadcast Domains Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet: CSMA/CD, Hubs and Collision Domains Rick Graziani Cabrillo College graziani@cabrillo.edu

Original Ethernet – Shared Bus Not for me  It's for me!  Not for me  When an Ethernet frame is sent all devices on the “bus” receive it. What do they do with it? All devices check the destination MAC address to see if it matches their MAC address

Collision! Collisions X Abbreviated MAC Addresses 1111 2222 3333 nnnn X When two devices transmit at the same time we have a collision Collision!

Media Access Control Section 5.1.1.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) process NICs operating in half duplex Used to first detect if the media is carrying a signal If no carrier signal is detected, the device transmits its data If two devices transmit at the same time - data collision Devices sense collision and stop transmitting – algorithm to determine when to send

(Hub)

X Collision Domain Shared Collision Domain 2222 1111 1111 2222 X 4444 3333 NICs and hub ports operate in half duplex Insufficient use of bandwidth About 50% bandwidth utilization (one direction only) Similar to 802.11 (CSMA/CA) 5555 Shared Collision Domain 3333 4444

Switches (and routers) segment collision domains

Ethernet: CSMA/CD, Hubs and Collision Domains Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet: Switch Forwarding Process Rick Graziani Cabrillo College graziani@cabrillo.edu

Forwarding decisions Hub: Layer 1 device Multiport repeater Router (multilayer switch): Layer 3 device Connects different subnets Makes forwarding decision based on layer 3 – Destination IP Address Maintains a routing table Switch: Layer 2 device Connects devices on same link layer Makes forwarding decision based on layer 2 – Destination MAC Address Maintains a MAC address table Hub: Layer 1 device Multiport repeater Makes forwarding decision based on layer 1 – forwards bits Everything that comes in one port, is sent out all other ports (regenerated)

Switch: Learning and Forwarding 1. Learn - Examine source MAC address and incoming port # In MAC address table? No: Add source MAC and port # to table (start 5 minute timer) Yes: Reset 5 minute timer 2. Forward – Examine destination MAC address Unicast No: Forward out all ports except incoming port Yes: Forward out port for that MAC address (learned previously) Broadcast/Multicast (unless using IGMP) Forward out all ports except incoming port

Learn: Examine Source MAC Address MAC Address Table Port MAC Address 1 2 3 4 A B C D MAC 00-0A MAC 00-0B MAC 00-0C MAC 00-0D Media Notes: Use graphic in slide MAC addresses are shortened for demonstration purposes.

Learn: Examine Source MAC Address MAC Address Table Port MAC Address I don’t have this source MAC address and the incoming port in my table so I will add it. Port and Source MAC address added 2 1 2 3 4 1 A B C D MAC 00-0A MAC 00-0B MAC 00-0C MAC 00-0D Media Notes: Use graphic in slide. Keep colors consistent. Destination MAC 00-0D Source MAC 00-0A Type Data FCS MAC addresses are shortened for demonstration purposes.

Forward: Examine Destination MAC Address MAC Address Table Port MAC Address I don’t have this destination MAC address in my table so I will send this unknown unicast out all ports. 1 00-0A Destination MAC address not in table 1 1 2 3 4 2 A B C D MAC 00-0A MAC 00-0B MAC 00-0C MAC 00-0D Media Notes: Use graphic in slide. Keep colors consistent. Destination MAC 00-0D Source MAC 00-0A Type Data FCS MAC addresses are shortened for demonstration purposes.

Learn: Examine Source MAC Address MAC Address Table I don’t have this source MAC address and the incoming port in my table so I will add it. Port MAC Address 1 00-0A Port and Source MAC address added 1 1 2 3 4 1 A B C D MAC 00-0A MAC 00-0B MAC 00-0C MAC 00-0D Media Notes: Use graphic in slide. Keep colors consistent. Destination MAC 00-0A Source MAC 00-0D Type Data FCS MAC addresses are shortened for demonstration purposes.

Forward: Examine Destination MAC Address MAC Address Table I know the destination MAC address so I will only forward the frame out port 1. Port MAC Address 2 1 4 00-0A 00-0D 1 2 3 4 2 A B C D MAC 00-0A MAC 00-0B MAC 00-0C MAC 00-0D Media Notes: Use graphic in slide. Keep colors consistent. Destination MAC 00-0A Source MAC 00-0D Type Data FCS MAC addresses are shortened for demonstration purposes.

Learn: Examine Source MAC Address MAC Address Table Port MAC Address 1 4 00-0A 00-0D 1 2 3 4 1 2 A B C D MAC 00-0A MAC 00-0B MAC 00-0C MAC 00-0D Media Notes: Use graphic in slide. Keep colors consistent. Destination MAC 00-0D Source MAC 00-0A Type Data FCS MAC addresses are shortened for demonstration purposes.

Ethernet: Switch Forwarding Process Rick Graziani Cabrillo College graziani@cabrillo.edu

Ethernet: Straight-Through versus Cross-Over Cable? Rick Graziani Cabrillo College graziani@cabrillo.edu

UTP Cabling Types of UTP Cable Section 4.2.2.4

Cables Straight-through cable: Unlike devices Crossover Straight-through Straight-through Crossover Straight-through cable: Unlike devices Cross-over cable: Like devices

Auto-MDIX What would happen if two new switches are interconnected with a straight-through cable? The auto-MDIX feature is enabled by default, therefore a cable change is not needed. Negotiate to work in full-duplex mode if capable. Work at the fastest speed that is supported by both switches.

Ethernet: Straight-Through versus Cross-Over Cable? Rick Graziani Cabrillo College graziani@cabrillo.edu

ARP: Introduction to ARP Rick Graziani Cabrillo College graziani@cabrillo.edu

IPv4 Address MAC Address ARP Request – Same Link 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 PCA puts the IPv4 packet on hold and creates an ARP Request with Target IPv4 = 192.168.1.50 Target MAC – unknown Source MAC 00-A Destination MAC = broadcast Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.50 Target MAC ??? Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address ARP Default Gateway 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 PCA puts the IPv4 packet on hold and creates an ARP Request with Target IPv4 = 192.168.1.1 Target MAC – unknown Source MAC 00-A Destination MAC = broadcast Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.1 Target MAC ??? Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

ARP: Introduction to ARP Rick Graziani Cabrillo College graziani@cabrillo.edu