network

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UnsightlyBison72703

Cards (140)

  • Network Layer

    • Layer 3 of the OSI reference model
    • Main function is to move packets from a sending host (source) to a receiving host (destination)
    • Routes packets according to 32-bit IP addresses e.g. 192.12.20.100
    • Provides host-to-host communication service
    • Handles routing among devices within a packet-switched network
    • At this layer, the unit of data exchanged among devices is typically called a Packet
    • Network layer protocols: IP, ICMP, IGMP etc.
  • Network-layer functions

    • Forwarding: move packets from router's input link to the appropriate router output link (per-router function)
    • Routing: determine route or path taken by packets among routers from source to destination (router to router)
  • Routers

    • Principle network layer devices
    • Interconnects networks
    • Generally, the default gateway
    • Uses forwarding and routing tables
    • Uses routing protocols
    • Today, there are layer 3 switches that work at the network layer
  • Routing protocol goal

    To determine the "best" paths (or routes), from sending hosts to receiving hosts, through a network of routers
  • Route (or Path)

    The sequence of network paths or hops that data packets take from a source to a destination across a computer network
  • "best route"

    Least "cost", "fastest" or "shortest path", "least congested"
  • Routing Protocols

    • RIP: Routing Information Protocol
    • OSPF: Open Shortest Path First
    • IGRP: Interior Gateway Routing Protocol (Cisco proprietary)
    • BGP: Border Gateway Protocol
  • Routing Cost Metrics

    Hop Count, Bandwidth, Delay/Latency, Reliability, Load etc.
  • Network addresses

    • A crucial aspect of computer networks that allows devices to communicate with each other within and between networks
    • To send/receive data, devices must have addresses
  • Four levels of addresses used in the TCP/IP protocol

    • Physical Addresses
    • Logical Addresses
    • Port Addresses
    • Application-Specific Addresses
  • Physical Addresses

    • Also known as the MAC (Media Access Control) address
    • Used by the data link layer and is the lowest level of addressing
    • Unique address of a device assigned by the manufacturer
    • Are fixed into the hardware and cannot be changed
  • Logical Addresses

    • Also known as an IP Address (Internet Protocol Address)
    • Used for higher-level network communication
    • Can be changed or reconfigured
  • Port Addresses

    • The address of a process
    • Each application runs with a port number (logically) on the computer
    • Allow different applications on the same computer to share network resources simultaneously
  • Application-Specific Addresses

    • User-friendly addresses that are designed for that specific application
    • E.g. Email address
  • IP address

    • For worldwide unique addressing of devices
    • IP addresses are only one way of addressing on OSI layer, others e.g. IPX
    • A routable protocol because its address space is suitable for routing
    • IP address is not a decimal number!
  • IPv4 Address

    • The first version of IP address
    • Widely used and primary IP version today
    • Numeric, 32–bit address (2^32 addresses) = more than 4 billion addresses
    • There are 4 octets, each with 8 bits (01001001)
    • Forms a 2-tier hierarchical address space: Tier 1: Network number (X) – left bits, Tier 2: Host number (Y) – right bits
    • IP address is not a decimal number! – but address is represented in demical
  • IPv6 Address

    • Most recent version of IP address
    • Is being deployed to fulfil the need for more Internet addresses
    • 128-bit address (2^128 addresses) = 340 undecillion unique address space
    • There are 8 quartets, and each group represents 2 Bytes (16-bits)
    • Designed to supersede IPv4 due to the global exponential growth of internet users
    • Currently working in tandem with IPv4 in some technologies, and eventually replacing it
  • IP address assignment

    The process of giving an IP address to a device on a network
  • Ways of assigning an IP address

    • Dynamic assignment: the IP address is automatically assigned through the Dynamic Host Configuration Protocol (DHCP)
    • Static assignment: the IP address is manually assigned by an administrator/user
  • Subnet Mask

    • A 32-bit mask that separates the IP address into Network Number (left x bits) and Host Number (right y bits)
    • Every IP address must be supplemented with a subnet mask. Otherwise, one would not know what part of the IP address is a network number, and what part is the host number
  • Subnet mask

    • Can be written shorter: 255.255.255.0 is the same as /24 because the binary 11111111.11111111.11111111.00000000 starts with 24 ones
    • Can be written in three different ways: Binary notation, Dotted decimal notation, Suffix notation
  • Types of IP Address

    • Private IP Address
    • Public IP Address
  • Private IP Address

    • Used to communicate within the same network
    • More secure than Public IP Addresses
    • Are not routed through the internet
    • For transverse over the internet, Network Address Translation (NAT) or Port Address Translation (PAT) is used
    • 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
  • Public IP Address

    • Used to communicate outside the network
    • A public IP address is basically assigned by the ISP (Internet Service Provider)
    • Sometimes NAT'ed private IP addresses
  • IP Address Classes

    • There are five classes of IP addresses: class A, B, C, D, and E
    • Each class has a range of valid IP addresses with default subnet mask
    • The value of the first octet determines the class
  • IP Address Classes & Ranges

    • Class A: Binary 0 indicates a class A address, default subnet mask is 255.0.0.0 (or: /8)
    • Class B: Binary 10 indicates a class B address, default subnet mask is 255.255.0.0 (or: /16)
    • Class C: Binary 110 indicates a class C address, default subnet mask is 255.255.255.0 (or: /24)
    • Class D: Binary 1110 indicates a class D address (multicast), default subnet mask is 255.255.255.0 (or: /24)
    • Class E: All other bit patterns belong to class E and are reserved for experiments
  • Special IP address ranges

    • 0.0.0.0 /8 – addresses used to communicate with the local network
    • 127.0.0.0 /8 – loopback addresses
    • 169.254.0.0 /16 – link-local addresses (Automatic Private IP Addressing -APIPA)
  • APIPA

    • A feature or characteristic in operating systems (eg. Windows) which enables computers to self-configure an IP address and subnet mask automatically when their DHCP server isn't reachable
    • The IP address range for APIPA is (169.254.0.1 to 169.254.255.254)
    • Has 65, 534 usable IP addresses, with the subnet mask of 255.255.0.0
  • IP Addressing Based on Operational Characteristics

    • Unicast– one-to-one communication
    • Multicast– used for one-to-many or many-to-many communication
    • Broadcast– one-to-all communication
  • Special IP address ranges

    • 0.0.0.0 /8 – addresses used to communicate with the local network
    • 127.0.0.0 /8 – loopback addresses
    • 169.254.0.0 /16 – link-local addresses (Automatic Private IP Addressing -APIPA)
  • APIPA

    • A feature or characteristic in operating systems (eg. Windows) which enables computers to self-configure an IP address and subnet mask automatically when their DHCP server isn't reachable
    • The IP address range for APIPA is (169.254.0.1 to 169.254.255.254)
    • Has 65, 534 usable IP addresses, with the subnet mask of 255.255.0.0
  • IP Addressing Based on Operational Characteristics

    • Unicast – one-to-one communication
    • Multicast – used for one-to-many or many-to-many communication
    • Broadcast – one-to-all communication
    • Anycast - one-to-nearest communication
  • "Power of 2" Sequence
    • 128, 64, 32, 16, 8, 4, 2, 1 = 255
    • A binary-to-decimal conversion
    • This sequence represents the values of individual bits in a byte
    • These values correspond to the powers of 2 for each position in an 8-bit binary number, each subsequent number doubling the previous one
  • Network Number (ID)

    • Network Address, Subnet Address
    • Every IP address belongs to exactly one IP network
    • IP networks are denoted with a Network Number (NN)
    • Network numbers look like IP addresses: 10.0.0.0 /8, 200.100.130.0 /24
    • Network numbers are IP addresses where all host bits are zero
    • Can not be used as a destination or source address in any IP network
    • Routers operate on network numbers
  • Broadcast Address

    • A type of communication mechanism that allows the message to be received by all the nodes of a network
    • Every IP network has one specific broadcast address (BA)
    • The broadcast address is used if a packet is delivered to all members of the IP network
    • Broadcast addresses are IP addresses where all host bits are one. 10.255.255.255/8, 200.100.130.255/24
    • Can not be used to address particular hosts or devices. They address the entire network, with every host in it
    • Many protocols use broadcast addresses, but mainly on the local network (delivered by layer 2)
    • Special broadcast address: 255.255.255.255 for all hosts in the local network
  • Network Design Principles

    • Behind every router interface must be one distinct IP network
    • Behind two different interfaces of the same router there must not be any IP network overlap
    • Routers operate on network numbers
  • Subnetting

    • The process of dividing a single (bigger) network into multiple smaller (sub) networks
    • The smaller networks created are called subnets
    • Each subnet has its unique network address known as its Subnet ID or Network Number
    • Used to solve the problem of addressing assignment inefficiency and depletion in IPv4
    • Helps in efficiently organizing the network
    • Divides broadcast domains, which helps improve network performance
    • Helps to maintain network security
    • Makes maintenance easier
  • Example 1

    • In class B, a network has a subnet mask of 255.255.240.0
    • Number of bits reserved for the network portion given the subnet mask is 20 bits
    • Maximum number of hosts per subnet is 4094
    • Number of bits reserved for the Host portion is 12 bits
    • Number of bits borrowed from the host portion is 4 bits
    • Number of possible subnets is 16
    • Number of usable hosts per subnet is 4092
  • Example 2

    • A host in your network has been assigned an IP address of 192.168.181.182 /25
    • Subnet to which the host belongs is 192.168.181.128 /25
    • Subnet mask in decimal is 255.255.255.128, in binary is 11111111.11111111.11111111.10000000
    • Number of host bits is 7
    • Number of hosts per subnet is 128
    • Number of usable hosts per subnet is 126
    • First usable IP address is 192.168.181.129
    • Last usable IP address is 192.168.181.254
    • Network IP address range is 192.168.181.128 - 192.168.181.255
    • Broadcast IP in decimal is 192.168.181.255, in binary is 11000000.10101000.10110101.11111111, MAC address is FF-FF-FF-FF-FF-FF
  • Basic Network Commands

    • HOSTNAME
    • IPCONFIG
    • PING
    • TRACERT OR TRACE ROUTE
    • PATHPING
    • NSLOOKUP
    • NETSTAT
    • ARP