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Networking

Intro​

This document contains my notes on Networking Fundamentals, which I studied in preparation for the Cisco Certified Network Associate (CCNA) certification.

Tools​

Cisco Packet Tracer, an innovative network configuration simulation tool.

Basic networking terms​

Computer network​

A computer network is a group of two or more computers that are linked together used to share resources, to exchange files, or to communicate with others.

MAC address​

A MAC address (short for medium access control address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment.
MAC address formats: XX:XX:XX:XX:XX:XX, XX-XX-XX-XX-XX-XX or XXXXXXXXXXXX - 6 groups of 2 hexadecimal digits (12-digit: 6 bytes or 48 bits).
First half of MAC address is typically the manufacturer's organizationally unique identifier (OUI) and the second half is unique number.

LAN​

A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building.

WAN​

A wide area network (WAN) is a telecommunications network that extends over a large geographic area.

DHCP​

The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a client–server architecture

Firewall​

A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted network and an untrusted network, such as the Internet.
Firewalls are categorized as a

  • Network-based firewalls are positioned between two or more networks, typically between the local area network (LAN) and wide area network (WAN), their basic function being to control the flow of data between connected networks. They are either a software appliance running on general-purpose hardware, a hardware appliance running on special-purpose hardware, or a virtual appliance running on a virtual host controlled by a hypervisor.
  • Host-based firewalls are deployed directly on the host itself to control network traffic or other computing resources. This can be a daemon or service as a part of the operating system or an agent application for protection.

IDS & IPS​

Intrusion detection systems (IDS) and intrusion prevention systems (IPS) are device or software application that continually monitor a network or systems, detect and log potential incidents, take action to stop the incidents, and notify/warn security administrators.

TCP​

Transmission Control Protocol (TCP)

IP​

The Internet Protocol (IP) is the network layer communications protocol for routing and addressing packets of data to destination across network.

TLS​

Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network.
TLS builds on the now-deprecated Secure Sockets Layer (SSL) specifications.

Communication protocol​

A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information. The protocol defines the rules, syntax, semantics, and synchronization of communication and possible error recovery methods.

PDU​

A protocol data unit (PDU) is a single unit of information transmitted among peer entities of a computer network.

ARP​

The Address Resolution Protocol (ARP) is a communication protocol used for discovering the link layer address, such as a MAC address, associated with a given internet layer address, typically an IPv4 address.

Network devices​

Repeater​

A Repeater (also called a hub) is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction.
Some types of repeaters broadcast an identical signal, but alter its method of transmission, for example, on another frequency or baud rate (speed of communication).
Repeaters operate on the physical layer, the first layer of the OSI model;

Network bridge​

A network bridge is a computer networking device that creates a single, aggregate network from multiple communication networks or network segments.

Network switch​

A network switch (also called switching hub, bridging hub, and, by the IEEE, MAC bridge) is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device.
A network switch is a multiport network bridge that uses MAC addresses to forward data at the data link layer (layer 2) of the OSI model. Some switches can also forward data at the network layer (layer 3) by additionally incorporating routing functionality. Such switches are commonly known as layer-3 switches or multilayer switches. In contrast to repeater, network switches has intelligence.
Network switches mainly operate on the data link layer, the second layer of the OSI model and used in LAN.

Router​

A router is a networking device that forwards data packets between computer networks using IP addresses.
Routers operate on the network layer, the third layer of the OSI model ;

Wireless Access Point​

A wireless access point, or just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network or wireless network.
As a standalone device, the AP may have a wired connection to a switch or router, but, in a wireless router, it can also be an integral component of the router itself.

Wireless LAN Controller​

A wireless LAN controller (WLC) is a network device used to monitor and manage wireless access points in an organization. WLCs are connected to routers and allow devices from across the organization to connect to the router via access points.

Lightweight Access Point​

A Lightweight Access Point (LWAP) is a type of wireless access point (AP) which is managed, configured and controlled by wireless LAN controller (WLC). Unlike LWAP, autonomous access points operates independently and does not need WLC.

Computer network types by scale​

drawing
  • Nanoscale
  • Near-field (NFC)
  • Body
  • Personal (PAN)
  • Near-me
  • Local (LAN)
    • Storage (SAN)
    • Wireless (WLAN)
    • Virtual (VLAN)
    • Home (HAN)
  • Building
  • Campus (CAN)
  • Backbone
  • Metropolitan (MAN)
    • Municipal wireless (MWN)
  • Wide (WAN)
  • Cloud
  • Internet
  • Interplanetary Internet

OSI and TCP/IP Model​

OSI and TCP/IP Model​

TCP/IP has 5 layers and we refer to the top layer (Application layer) as layer 7 because TCP/IP is originated from OSI Model.

LayersOSI ModelTCP/IPDescriptionProtocolsDevicesPDUs
7ApplicationApplicationHuman-Computer interactionHTTP, HTTPS, Telnet,FTP, TFTPData
6PresentationCompression and Encryption protocolsSSH
5SessionConnection maintenanceNFS,RPC,SCP
4TransportTransportEnd-to-end connectionTCP/UDPSegments
3NetworkNetworkLogical addressingIPv4/IPv6,ARP,IGMP,ICMPRouterPackets
2Data LinkData LinkPhysical addressingEthernetBridge/SwitchFrames
1PhysicalPhysicalPhysical transmission of signals,media or binary raw bitsCable(CAT 5,6),DSL,Optic fiberNetwork HubBits

Ports​

Port ranges​

StartEndDesignation
01023System or well-known ports
102449151User or registered ports
4915265535Dynamic, private or ephemeral ports

Ephemeral port​

An ephemeral port is a communications endpoint (port) of a transport layer protocol of the Internet protocol suite that is used for only a short period of time for the duration of a communication session.

Numeral system and networking​

IP Addressing​

What is IP Address?​

  • layer 3 logical address assigned by an administrator
  • resides at layer 3 of OSI Model
  • used to identify specific devices on a network
  • every device on the internet has a unique IP address

IPv4 Characteristic​

IPv4

  • layer 3 or Network layer protocol
  • connectionless protocol
    • TCP on other hand is connection oriented
  • packets are treated independently
    • may take different path (load balancing, bandwidth, hopcount)
  • hierarchical addressing structure
    • network and host portion
  • best effort delivery with no guarantee
  • no data recovery features
  • no built-in sessions
  • no retransmission

IPv4 address format​

  • 32 bit
  • x.x.x.x - 4 octets(8 bits or 1 byte)

Network and Host portion​

  • 10.x.x.x - IP address
  • 255.0.0.0 - network mask
  • N.H.H.H - Network/Host portions

Private IPv4 address class ranges​

RFC 1918 nameIP address rangeNumber of addressesLargest CIDR block (subnet mask)Network/HostClassful description
24-bit block10.0.0.0 – 10.255.255.2551677721610.0.0.0/8 (255.0.0.0)N.H.H.Hsingle class A network
20-bit block172.16.0.0 – 172.31.255.2551048576172.16.0.0/12 (255.240.0.0)N.N.H.H16 contiguous class B networks
16-bit block192.168.0.0 – 192.168.255.25565536192.168.0.0/16 (255.255.0.0)N.N.N.H256 contiguous class C networks

Public IPv4 address class ranges​

ClassStart addressEnd addressDefault address maskNetwork/HostCIDR notation
Class A0.0.0.0127.255.255.255255.0.0.0N.H.H.H/8
Class B128.0.0.0191.255.255.255255.255.0.0N.N.H.H/16
Class C192.0.0.0223.255.255.255255.255.255.0N.N.N.H/24
Class D (multicast)224.0.0.0239.255.255.255not defined/4
Class E (reserved)240.0.0.0255.255.255.255not definednot defined

Special addresses​

  • Directed Broadcast Address

    • used by hosts to send data to all devices on a specific network.
    • binary 1s in the entire host portion of the address (e.g. Network: 172.31.0.0, Directed broadcast:172.31.255.255)
    • on routers disabled by default

  • Local Broadcast Address

    • used to communicate with all devices of local network
    • addresses is all binary 1s (e.g. 11111111.11111111.11111111.11111111 - 255.255.255.255)
    • e.g. used by host to request an IP address from a DHCP server
    • always dropped by routers and layer 3 switches

  • Local loopback address

    • A loopback address or 'localhost' IP addresses range 127.0. 0.0 to 127.255. 255.255.
    • used to let a system to send a message to itself for testing
    • ::1 is IPv6 assigned to loopback
    • NOTE: routers and switches also have loopback addresses which are not the same as local loopback address.

Subnet Masks​

  • used to determine network and host portion
  • used to determine weather a device is remote (i.e. to be reached via default gateway) or local (i.e. same subnet) (e.g. if two hosts are on the same subnet then they communicate directly with each other rather then forwarding the traffic to default gateway to route it)
  • e.g. IP: 10.1.1.1, Network mask: 255.0.0.0 (N.H.H.H), Network: 10.0.0.0, NetId: 10, HostId: .1.1.1

CIDR notation​

CIDR - Classless Inter-Domain Routing

  • introduced on 1993 and so far more preferable
  • uses 10.0.0.0/8 (8 binary bits) notation instead of 10.0.0.0 255.0.0.0
  • enables Variable Length Subnet Mask (VLSM) (e.g. 255.224.0.0 = /11) but in Class A is always /8, Class B is always /16 and Class C is always /24.

Initial Device Configuration​

Commands​

# How to get MAC address of device in network. See https://www.baeldung.com/linux/arp-command
ping 10.0.0.1
arp -a

# Switch CLI
show mac address-table

Notes​

References​