Network Topologies and IP Addressing

• Topology refers to the arrangement of elements within a communication network.

Network Topologies

• Bus Topology: All devices share a single cable; simple but a break in the cable disrupts the entire network.
• Ring Topology: Each device is connected to exactly two other devices, forming a ring. Data travels in one direction, failure of one device can disrupt the entire network.
• Star Topology: All devices connect to a central hub or switch. Easy to manage and a device failure doesn't affect the entire network.
• Mesh Topology: Devices are connected to each other redundantly. High fault tolerance but complex and expensive.
• Tree Topology: Combines features of bus and star topologies; hierarchical.

IP Addressing

• An IP address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication.
• IPv4 addresses are 32-bit numbers, typically written in dotted decimal notation.
• IPv6 addresses are 128-bit numbers, typically written in hexadecimal notation.

IP Address Structure

• An IP address consists of two parts: network address and host address.
• The network address identifies the network to which the device belongs.
• The host address identifies a specific device within that network.

IP Address Classes (IPv4)

• Class A: Large networks, first octet 1-126, supports 16,777,214 hosts.
• Class B: Medium-sized networks, first octet 128-191, supports 65,534 hosts.
• Class C: Small networks, first octet 192-223, supports 254 hosts.
• Class D: Multicasting, first octet 224-239.
• Class E: Reserved for experimental purposes, first octet 240-255.

Private IP Addresses

• Private IP addresses are not routable on the internet.
• Used for internal networks.
• Class A: 10.0.0.0 - 10.255.255.255
• Class B: 172.16.0.0 - 172.31.255.255
• Class C: 192.168.0.0 - 192.168.255.255

Subnetting

• The practice of dividing a network into smaller, logical subnetworks.
• Improves network performance, organization, and security.
• Subnet mask is used to determine the network and host portions of an IP address.

Routing

• The process of selecting the best path for data to travel across a network.
• Performed by routers, which forward data packets between networks.

Routing Protocols

• RIP (Routing Information Protocol): Distance-vector protocol, uses hop count as a metric.
• OSPF (Open Shortest Path First): Link-state protocol, uses cost as a metric.
• EIGRP (Enhanced Interior Gateway Routing Protocol): Hybrid protocol, developed by Cisco.
• BGP (Border Gateway Protocol): Path-vector protocol, used for routing between different autonomous systems (AS).

Routing Tables

• Routers maintain routing tables to determine the best path for forwarding packets.
• Routing table contains information about directly connected networks, static routes, and dynamically learned routes.

Packet Filtering by ACL

• Access Control Lists (ACLs) are used to filter network traffic based on specified criteria.
• ACLs can be configured on routers and switches.
• ACLs can filter traffic based on source/destination IP address, port number, protocol, etc.
• Standard ACLs filter based on the source IP address.
• Extended ACLs filter based on source/destination IP address, port number, and protocol.

ACL Actions

• Permit: Allows traffic to pass.
• Deny: Blocks traffic.

NAT

• Network Address Translation (NAT) is used to translate private IP addresses to public IP addresses, and vice versa.
• Allows multiple devices on a private network to share a single public IP address.
• Conserves public IP addresses.
• Provides a level of security by hiding the internal network structure.

NAT Types

• Static NAT: One-to-one mapping between a private and public IP address.
• Dynamic NAT: Maps a private IP address to a public IP address from a pool of available addresses.
• PAT (Port Address Translation): Multiple private IP addresses are mapped to a single public IP address using different port numbers. Commonly referred to as NAT overload.

IP Services

• DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP addresses and other network configuration parameters to devices.
• DNS (Domain Name System): Translates domain names to IP addresses.
• SNMP (Simple Network Management Protocol): Used for monitoring and managing network devices.
• NTP (Network Time Protocol): Used to synchronize the clocks of network devices.

IPv6 Routing

• IPv6 (Internet Protocol version 6) is the latest version of the Internet Protocol.
• IPv6 addresses are 128-bit long.
• IPv6 includes simplified header, efficient routing and auto-configuration.
• IPv6 routing protocols include RIPng, OSPFv3, and BGP.

IPv6 Address Types

• Unicast: Identifies a single interface.
• Multicast: Identifies a group of interfaces.
• Anycast: Identifies a group of interfaces, packet is delivered to the nearest one.

Switching

• Switching is the process of forwarding data packets between different ports on a switch.
• Operates at the data link layer (Layer 2) of the OSI model.
• Switches use MAC addresses to forward packets.

Switching Methods

• Store-and-Forward: The switch receives the entire frame before forwarding it. Provides error checking.
• Cut-Through: The switch starts forwarding the frame as soon as it reads the destination MAC address. Faster, but no error checking.
• Fragment-Free: The switch checks the first 64 bytes of the frame before forwarding it. Compromise between store-and-forward and cut-through.

Spanning Tree Protocol

• Spanning Tree Protocol (STP) is a network protocol that prevents loops in a network.
• Loops can cause broadcast storms, which can bring down a network.
• STP blocks redundant paths to prevent loops.

STP Operation

• Elects a root bridge, which is the switch with the lowest bridge ID.
• Calculates the shortest path to the root bridge for each switch.
• Blocks redundant paths.
• Port states: Blocking, Listening, Learning, Forwarding.

STP Variants

• RSTP (Rapid Spanning Tree Protocol): Faster convergence than STP.
• MSTP (Multiple Spanning Tree Protocol): Allows multiple spanning tree instances to run on a network.

WAN

• Wide Area Network (WAN) is a network that covers a large geographical area.
• Connects multiple LANs together.

WAN Technologies

• Leased Lines: Dedicated connection between two points.
• Frame Relay: Packet-switched technology.
• ATM (Asynchronous Transfer Mode): Cell-switched technology.
• MPLS (Multiprotocol Label Switching): Packet-forwarding technology that uses labels to make forwarding decisions.
• VPN (Virtual Private Network): Creates a secure connection over a public network.