2101 Ch07-12 Final Part 2

Ethernet Technology

• Ethernet and WLAN are the two main LAN technologies.
• Ethernet supports bandwidths up to 100 Gbps.
• Ethernet uses wired communication (twisted pair, fiber-optic, coaxial).
• It operates at the data link layer (LLC and MAC sublayers) and the physical layer.
• Defined by IEEE 802.2 and 802.3 standards.
• Ethernet supports various bandwidths: 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, 40 Gbps, 100 Gbps.

MAC Sublayer

• Hardware-based sublayer handling data encapsulation and media access control.
• Provides data link layer addressing.
• Integrates with various physical layer technologies.
• Responsible for data encapsulation and accessing the media.

Ethernet Frame Structure

• Minimum frame size: 64 bytes.
• Maximum frame size: 1518 bytes (excluding preamble)
• Fields include preamble, start frame delimiter, destination MAC address, source MAC address, EtherType, data, and FCS.
• Frames less than 64 bytes (runt frames) are discarded.
• Frames exceeding 1518 bytes (jumbo frames) are usually supported by switches and NICs.
• Ethernet addressing uses source and destination MAC addresses.
• Ethernet error detection employs a frame check sequence (FCS) trailer.

Ethernet MAC Addressing

• 48-bit binary value, represented by 12 hexadecimal digits (6 bytes).
• Unique to each Ethernet device or interface.
• Assigned in accordance with vendor's organizationally unique identifier (OUI).
• OUI is a 6-hexadecimal-digit code assigned by IEEE.
• Vendor assigns unique 6 hexadecimal digits after the OUI to complete the MAC address.

Ethernet Media Access

• Legacy Ethernet (bus topology/hubs): Shared, half-duplex medium using CSMA/CD. This method ensures one device transmits at a time.
• Current Ethernet (switches): Full-duplex operation, no CSMA/CD needed.

Ethernet Switches and Forwarding Methods

• Use MAC address table for forwarding decisions.
• Store-and-forward switching: Receives entire frame, checks CRC and forwards based on destination MAC. Discards erroneous frames. Best for QoS (quality of service).
• Cut-through switching: Forwards frame before entire reception. Fast-forward: Lowest latency but may forward errored packets. Fragment-free: Stores first 64 bytes to avoid collision fragments before forwarding. May be configured per port.
• Buffering used for frames and congestion. Shared memory improves handling of larger frames and asymmetric port bandwidths.

Duplex and Autonegotiation

• Full-duplex: Simultaneous sending and receiving.
• Half-duplex: Only one end transmits at a time.
• Autonegotiation: Auto-detection of best speed and duplex capabilities. Best practice is to configure all ports as full-duplex.
• Duplex mismatch common performance issue in 10/100 Mbps links.

Crossover vs. Straight-Through Cables

• Crossover cables connect like devices, straight-through for unlike devices.
• Auto-MDIX (automatic medium-dependent interface crossover) feature on most switches eliminates cable type concern for copper connections. Use correct cable type for best practice.

Network Layer (OSI Layer 3)

• Provides services for end-device communication across networks.

• Key protocols: IPv4 and IPv6. Other protocols: OSPF, ICMP.

• Four basic network layer operations:

• Addressing end devices

• Encapsulation

• Routing

• Decapsulation

• IP header carries information for packet delivery.

IP Version 4 (IPv4)

• Packet header fields: Version, DS, TTL, Protocol, Header Checksum, Source and Destination IPv4 Addresses.
• TTL limits packet lifetime, decremented by each router hop.
• Unreliable (best-effort delivery); other protocols handle reliability.
• IPv4 is connectionless, best-effort, and independent of media.
• IPv4 has limited addresses, inherent complexity with NAT implementation.

IPv4 Packet Fragmentation

• Routers may fragment IPv4 packets if destination MTU is smaller.
• IPv6 packets cannot be fragmented.

IP Version 6 (IPv6)

• Larger address space (128 bits) compared to IPv4.
• Simplified header for efficient routing.
• No need for NAT (Network Address Translation)
• Key fields in IPv6 packet header: Version, Traffic Class, Flow Label, Payload Length, Next Header, Hop Limit, Source and Destination IPv6 Addresses

Routing Table

• Used by hosts and routers to find destinations.
• Types of routes: directly-connected, remote, default.

Host Routing

• IPv4: Uses subnet mask, IPv4 address of destination and source hosts to determine whether the destination is on the local network or remote network.
• IPv6: Router advertises local network prefix.

Default Gateway

• Router(s) that route traffic to other networks.
• Hosts need default gateway for external network communications.

Router Routing Tables

• Three types of routes: Directly-connected networks, remote networks, and default.
• Different route sources: (L, C, S, O, D)

Static Routing

• Manually configured route entries.
• Not automatically updated if network topology changes.
• Suitable for small networks with few redundant paths.

Dynamic Routing

• Routers learn about remote networks from other routers.
• Updates routing tables automatically to adapt to network-topology changes.
• Protocols: OSPF, EIGRP.

ARP (Address Resolution Protocol)

• Maps IPv4 addresses to MAC addresses.
• ARP table keeps address mappings for a short time.
• ARP request is broadcasted, reply is unicast.

ICMPv6 Neighbor Discovery (NDP)

• Maps IPv6 addresses to MAC addresses (replacement for IPv4 ARP).
• Uses ICMPv6 messages. Neighbor solicitation (broadcasted), neighbor advertisement (unicast)

MAC Addresses and IP Addressing

• MAC addresses are used for Layer 2 communication within a local network.
• IP addresses are used for end-to-end communication across networks.

Network Segmentation and Subnetting

• Splitting a single network into smaller networks (subnets).
• Subnet mask: Differentiates network and host portions of an IPv4 address.
• Prefix Length: Number of network bits in an address (e.g., /24 = 24 network bits).
• Binary AND operation: To get network address match the IPv4 and subnet mask.

IPv4 Address Types

• Unicast: one-to-one communication.
• Broadcast: one-to-all communication(IPv4).
• Multicast: one-to-many communication.
• Public vs. Private addresses; private addresses cannot be routed over the internet.

Special IPv4 Addresses

• Loopback: 127.0.0.0/8, used for testing the host's TCP/IP protocol stack
• Link-Local: 169.254.0.0/16, assigned automatically if DHCP is unavailable.

This quiz covers key aspects of Ethernet technology, including its bandwidth capabilities and frame structure. Explore the functions of the MAC sublayer and the relevant IEEE standards that govern Ethernet operations. Test your knowledge on this fundamental LAN technology.