Networking Fundamentals: Ethernet, IP, VLANs, and More
Topic 2: The 802 Project and Ethernet Standards
The 802 project, supported by ISO, divides the data link layer into two sublayers: Logical Link Control (LLC) and Media Access Control (MAC). It defines the specific aspects of each local area network.
Main Features of Ethernet Standards:
- 10BASE5: Uses 500m of coaxial cable (50 ohm) with PCs connected every 2.5m.
- 10BASE2: Uses 185m of coaxial cable (50 ohm) with a maximum of 30 PCs and BNC connectors.
- 10BASET: Uses twisted pair cables with hubs and switches.
Fast Ethernet (1990)
Fast Ethernet is 10 times faster than the original Ethernet, using UTP and fiber optic cables. Key features include:
- MLT-3 Coding: A line coding that uses three voltage levels, reducing interference and bandwidth.
- 4B/5B Encoding: A data communication line code that adds an extra bit for security and auto-blocking signals.
Gigabit Ethernet (1999)
Gigabit Ethernet allows for half-duplex and full-duplex communication. It often uses Twinax cabling, which is similar to coaxial cable but with two inner conductors.
MAC vs. IP Address
A MAC (Media Access Control) address is a physical address consisting of 6 bytes (48 bits) represented in hexadecimal. It is used at the data link layer to identify devices on a local network. Each device has a unique MAC address.
An IP (Internet Protocol) address is a logical address used to identify devices on a global network like the Internet. It can be 32 bits (IPv4) or 128 bits (IPv6). The IP address consists of two main components: the network part and the host part.
TTL (Time to Live): The time after which the address mapping will be forgotten.
VLANs (Virtual LANs)
A VLAN extends the concept of a local area network (LAN) by providing data link connectivity for a sub-network. A VLAN is associated with a broadcast domain and typically consists of one or more Ethernet switches.
Key Features of VLANs:
- Traffic Isolation: Frames sent to/from ports 1-8 can only reach ports 1-8.
- MAC Address-Based VLANs: VLANs can be defined based on MAC addresses.
- Dynamic Membership: Ports can be dynamically assigned to VLANs.
- Forwarding Between VLANs: Done via routing; some switches incorporate VLAN routing capabilities.
Disadvantage: Limitation to 4096 VLANs per switching domain.
Trunk Port: Carries frames between VLANs defined over multiple physical switches. Each frame sent via the port is tagged with the VLAN ID.
STP (Spanning Tree Protocol): A network protocol used to prevent network loops in redundant network topologies. It allows redundant links to be identified and selectively blocked, creating a single, loop-free path.
Duplex Communication System: A point-to-point system where connected parties or devices can communicate in both directions. In a half-duplex system, communication is bidirectional but not simultaneous.
IP Address Types
- Unicast: Uniquely identifies an interface on an IPv6 device.
- Anycast: Identifies one or more interfaces, used for load balancing (one-to-nearest).
- Multicast: Represents a dynamic group of hosts, delivering packets to multiple interfaces.
Topic 3: Network Layer Protocols and Concepts
Encapsulation: The process by which a lower-layer protocol receives data from a higher-layer protocol and places it in the data part of its frame.
IP (Internet Protocol)
IP is the protocol by which data is sent from one computer to another on the Internet. Messages are divided into datagrams. The network layer is responsible for routing packets, hop by hop, from source to destination. Routers, with their hardware and firmware, manage the routing table.
ARP (Address Resolution Protocol)
ARP maps an IP address to a recognized physical machine address on the local network. Each host/router has an ARP table for this mapping.
MTU (Maximum Transmission Unit)
MTU is the largest possible frame size at the link layer. Different link types have different MTUs. Large IP frames are fragmented within the network, and bits in the IP header are used to identify and order the fragments.
Netmask
A netmask is a 32-bit number that masks an IP address, dividing it into a network address and a host address. The subnet mask sets network bits to “1” and host bits to “0”. It determines whether a host is on the local subnet or a remote network.
Subnetting and Supernetting
Subnetting divides a large network into smaller subnets to improve performance, reduce broadcast traffic, and optimize resources. It uses subnet masks to define subnet boundaries.
Supernetting aggregates multiple Internet addresses of the same class, grouping IP addresses to create larger address spaces. It helps minimize routing table sizes.
NAT (Network Address Translation)
NAT assigns a public address to a computer (or group) within a private network. Types of NAT include:
- Static NAT: A single private IP address is mapped to a single public IP address.
- Dynamic NAT: Multiple private IP addresses are mapped to a pool of public IP addresses.
- PAT (Port Address Translation): Also known as NAT overloading, many private IP addresses are translated to a single public IP address using port numbers to distinguish traffic.
DHCP (Dynamic Host Configuration Protocol)
DHCP automatically assigns network configuration settings to devices. It simplifies network administration by centrally managing and allocating IP addresses using a client-server model.
ICMP (Internet Control Message Protocol)
ICMP is an error notification protocol. Network devices like routers use it to generate error messages to the source IP address when network problems prevent IP packet delivery.
IPv6 (Internet Protocol version 6)
IPv6 handles packets more efficiently, improves performance, and increases security. It allows ISPs to reduce routing table sizes by making them more hierarchical. Key features include:
- Increased security.
- Improved QoS mechanisms, especially for real-time data.
- Improved multicast.
IPv6 addresses are 128 bits long, distributed in eight groups of 16 bits each. Each group is expressed in four hexadecimal digits, separated by colons.