Duc Mai on Duke Mike

Control Plane Policing (CoPP)

Sun, 01 Mar 2026 00:00:00 +0000

Table of Contents Link to heading

Control Plane Policing (CoPP) Link to heading

Info

CoPP protects the route processor (RP) or the control plane (CPU) of a router or switch by rate-limiting and filtering traffic destined to the device itself.

Without CoPP:

Authentication, Authorisation, and Accounting (AAA)

Fri, 27 Feb 2026 00:00:00 +0000

Table of Contents Link to heading

Authentication, Authorisation, and Accounting (AAA) Link to heading

Concept	?	Example	Key Technologies
Authentication	Who are you?	Logging in with a username and password	RADIUS, TACACS+, local login
Authorisation	What can you do?	Allowing access to specific commands or files	ACLs, RBAC
Accounting	What did you do?	Logging time, commands used, data accessed	Syslog, AAA logs, SNMP

When Cisco devices use AAA, you can authenticate users using:

TrustSec and MACsec

Wed, 25 Feb 2026 00:00:00 +0000

Table of Contents Link to heading

TrustSec Link to heading

Cisco TrustSec (CTS) is a next-generation NAC solution that performs network enforcement by using Security Group Tags (SGTs) instead of IP addresses and ports.

Quality of Service (QoS)

Sun, 22 Feb 2026 00:00:00 +0000

Table of Contents Link to heading

Latency Link to heading

Info

Latency is the time it takes for packets to travel across a network from a source to a destination.

It is recommended that a network latency should not exceed 400 ms, and for real-time traffic, network latency should be less than 150 ms.

GRE over IPsec

Thu, 19 Feb 2026 00:00:00 +0000

Table of Contents Link to heading

Virtual Private Network (VPN) Link to heading

VPN is an overlay network that enables private networks to communicate with each other across an untrusted network (the Internet)

Software-Defined WAN (SD-WAN)

Thu, 19 Feb 2026 00:00:00 +0000

Table of Contents Link to heading

Software-Defined WAN (SD-WAN) Link to heading

Info

Cisco SD-WAN (based on Viptela) is an overlay architecture that provides a secure logical connectivity among offices, data centres, and the cloud, regardless of the physical topology (satellite, LTE, and MPLS).

SD-WAN Architecture Link to heading

vManage NMS Link to heading

Note

The vManage network management system (NMS) is the “single pane of glass” for SD-WAN because it provides a user interface to configure and manage the full SD-WAN solution.

vBond Orchestrator Link to heading

Note

The vBond orchestrator is a virtualised vEdge running a dedicated function of the vBond persona.

Every vBond has a permanent control plane connection over a Datagram Transport Layer Security (DTLS) tunnel with every vSmart controller.

Software-Defined Access (SD-Access)

Sat, 14 Feb 2026 00:00:00 +0000

Table of Contents Link to heading

Software-Defined Access (SD-Access) Link to heading

Traditional NAC:

Stateful Switchover - SSO

Tue, 10 Feb 2026 00:00:00 +0000

Table of Contents Link to heading

Redundant RP (Route Processor) or Supervisor Engines Link to heading

A route processor is card that performs control plane functions.
Two states are active/standby.
While failover happens, routing protocols restarts and adjacencies down. Thus. we need HA technologies to avoid downtime.

Pre-SSO Link to heading

HSA (High System Availability): standby RP stays inactive until the active RP is down.
RPR (Route Processor Redundancy): standby RP is partially initialised and startup-cfg is synced.
RPR+ (Route Processor Redundancy+): standby RP is initialised and startup-cfg+running-cfg are synced. Still not synced other protocols, thus there is still downtime while failover.

With-SSO Link to heading

SSO/NSF (Non-Stop Forwarding) Link to heading

SSO fully boots and initialises the standby RP.
NSF is non-configurable. It is enabled by default if SSO is enabled, hence SSO/NSF.
SSO maintains L2 forwarding by checkpointing FIB to standby RP.
However NSF doesn’t checkpoint any L3 control plane info -> adjacencies down and routes are cleared.

SSO/NSF with GR (Graceful Restart) Link to heading

GR maintains L3 forwarding to a lost neighbour during an RP failover.
- This length of time is called grace period.
- Despite down adjacencies, packets are still forwarded.
GR is a two-way handshake.
- Device failing over must be GR-capable.
- Neighbouring device must at least be GR-aware, called helpers.
With GR in place, traffic continues to be forwarded even if the device is actually down (not just doing an RP failover).
- To resolve this, do not set grace period too long.

SSO/NSF with NSR (Non-Stop Routing) Link to heading

NSR maintains L3 forwarding and neighbour adjacencies by checkpointing both FIB and RIB to standby RP.
Traffic and adjacencies operates seamlessly without awareness, but NSR really increases the workload on the router.

SSO/NSF with GR or NSR Link to heading

A device can’t use both at the same time for the same neighbour.
Use GR for neighbour routers that are GR-aware.
Use NSR for peers that are GR-unaware.

Configuration Link to heading

Info

Router(config)# redundancy
Router(config-red)# mode sso

Analysis of Optus 2025 Outage

Fri, 19 Sep 2025 00:00:00 +0000

Table of Contents Link to heading

On September 18, 2025, Optus experienced a major network outage that disrupted Triple Zero (000) emergency services across several Australian states. The outage lasted over 13 hours and resulted in four confirmed deaths and hundreds of failed emergency calls. This tragic event has reignited scrutiny over Optus’s infrastructure and regulatory compliance—especially in light of a similar outage in November 2023, which had already exposed critical vulnerabilities in the telco’s emergency systems.

Meta Unmasked: The June 2025 Android Tracking Phenomenon

Fri, 13 Jun 2025 00:00:00 +0000

Table of Contents Link to heading

Introduction Link to heading

I still remember one late evening in June 2025—one of those nights when you’re at your desk, troubleshooting tech issues, and a peculiar case lands on your desk. A customer named X called in, alarmed that his personal browsing data seemed to follow him from his web browser straight into his favourite apps. As I dug deeper, I discovered something extraordinary: major companies like Meta and Yandex had found a clever way to track Android users’ browsing activity by exploiting an overlooked communication channel. Today, let’s unravel this mystery, explore the technical intricacies behind it, and chart out some real solutions that can turn the tide for digital privacy.

Network Automation with Netmiko: A Practical Guide

Sun, 18 May 2025 14:01:51 +0000

Table of Contents Link to heading

Introduction Link to heading

In today’s fast-paced networking landscape, automation is no longer optional—it’s essential. Managing network devices manually is inefficient and error-prone, but Python-based automation frameworks like Netmiko make it easy to interact with network devices programmatically. In this blog, we’ll explore how to use the Netmiko module to automate configuration and verification tasks on Cisco devices.

Advanced Network Automation with Ansible and AWX

Sat, 15 Mar 2025 00:00:00 +0000

Table of Contents Link to heading

Using AWX for Scheduled Playbook Execution Link to heading

Once AWX is installed, configure an inventory, import your playbooks, and schedule automation workflows.

Practical Network Automation with Ansible and AWX

Fri, 14 Mar 2025 00:00:00 +0000

Table of Contents Link to heading

Simple Network Automations Link to heading

Reprieving Network Information Link to heading

A simple playbook to gather device facts and interface details:

Streamlining NetDevOps Workflows with Ansible and AWX

Thu, 13 Mar 2025 00:00:00 +0000

Table of Contents Link to heading

Managing network infrastructure is a repetitive and time-consuming task. As networks grow, manually configuring switches, routers, and firewalls becomes unmanageable. Ansible, an open-source automation tool, simplifies network management by automating repetitive tasks, ensuring consistency, and reducing human error.

The Worst Network Troubleshooting Nightmares

Mon, 11 Nov 2024 00:00:00 +0000

Table of Contents Link to heading

Every IT admin knows the feeling—everything is running smoothly until suddenly, the network goes down. Emails stop sending, websites won’t load, and employees flood the helpdesk with complaints.

An Unhackable Approach to Password Management

Wed, 07 Aug 2024 00:00:00 +0000

Table of Contents Link to heading

In today’s digital world, safeguarding sensitive information is more critical than ever. Passwords serve as the first line of defence against unauthorised access, yet managing them securely can be a challenge.

The Worst System Outages & How They Were Fixed

Tue, 25 Jun 2024 00:00:00 +0000

Table of Contents Link to heading

Every IT professional has faced system outages that bring operations to a grinding halt. Whether it’s a misconfigured update, a hardware failure, or a cyberattack, these incidents can cost businesses millions and leave IT teams scrambling for solutions.

A Guide to GPG Cryptography and Key Management

Sat, 20 Apr 2024 00:00:00 +0000

Table of Contents Link to heading

What is GPG? Link to heading

GNU Privacy Guard (GPG) is one of the most widely used tools for securing emails, files, and other digital communications, especially in an era where privacy is constantly under threat, strong encryption is no longer optional—it’s essential. Built on the OpenPGP standard, GPG offers powerful encryption capabilities while remaining free and open-source.

A Cautionary Tale of Printer Sharing

Thu, 14 Mar 2024 00:00:00 +0000

Table of Contents Link to heading

Introduction Link to heading

As IT professionals, we’ve all been in the trenches, troubleshooting printer issues for colleagues. One of the most common makeshift solutions is sharing a printer from one machine to another over a LAN. It seems logical, cost-effective, and convenient—until reality hits.

Vsphere Components

Fri, 01 Mar 2024 00:00:00 +0000

Table of Contents Link to heading

Virtualisation Concepts Link to heading

Virtual Resources Link to heading

Info

VMware uses a hypervisor to take the resources available in a physical server and abstract them. These abstracted resources are known as virtual resources and are the core building blocks of virtual machines

Processor (CPU) Link to heading

Info

A required component that carries out the main processing for the VM.

Memory (RAM) Link to heading

Info

A required component that stores the data that is currently being used by the running OS and its applications.

Due to how RAM is virtualised, the hypervisor is able to allocate more RAM to VMs than exists in the physical host. This is done by creating a swap file on disk that is used as RAM in the case that not enough physical RAM is available. This is called over-commitment of resources

Access Control Lists - ACLs

Fri, 16 Feb 2024 00:00:00 +0000

Table of Contents Link to heading

Access Control Lists (ACLs) Link to heading

Info

A sequential lists of access control entries (ACEs), which are series of permit and deny statements, placed in a router’s interface, that apply to addresses or upper-layer protocols.

Common ACL functions include the following:

IP Addressing Best Practices

Sun, 14 Jan 2024 00:00:00 +0000

Table of Contents Link to heading

Addressing Design Considerations Link to heading

Number of locations
Number of devices per location
IP addressing requirements for each individual location or building:
1. Number of devices to be supported in each communication closet
2. Site requirements: data networks, wireless LANs, IP Telephony (IPT) networks, CCTV networks (security cameras), video conference systems, access control systems, network management, server farms, point-to-point links, and router/switch loopback addresses.
Subnet size

Title	Reference
Guidelines for Management of IP Address Space	RFC 1466
Internet Registry IP Allocation Guidelines	RFC 2050

Devices That Require Addressing Link to heading

The end devices requiring an IP address include these:

First-Time Router Configuration for Network Engineers

Tue, 02 Jan 2024 00:00:00 +0000

Table of Contents Link to heading

Configuring a new router for the first time is a crucial step in ensuring a secure, efficient, and scalable network. This guide provides step-by-step instructions, including line-by-line CLI commands.

First-Time Switch Configuration for Network Engineers

Mon, 01 Jan 2024 00:00:00 +0000

Table of Contents Link to heading

When setting up a new network switch, it’s crucial to configure it properly for security, management, and performance. This guide provides step-by-step CLI commands, including verification steps after each configuration.

The Hidden Costs of Legacy Systems

Wed, 29 Nov 2023 00:00:00 +0000

Table of Contents Link to heading

Many businesses continue to rely on legacy systems, believing that if something still works, there’s no urgent need to replace it. However, what they don’t see are the hidden costs—the inefficiencies, security risks, and financial burdens that quietly drain resources.

Analysis of Optus 2023 Outage

Tue, 14 Nov 2023 00:00:00 +0000

Table of Contents Link to heading

Introduction Link to heading

Info

The Optus 2023 outage was a major network failure that affected about 10 million Optus customers on November 8, 2023, disrupting phone calls, Internet access and emergency services.

Root Cause Link to heading

Note

According to Optus, at around 4.05am, the Optus network underwent a routine software upgrade. This upgrade led to changes in routing information from an international peering network. These changes propagated through multiple layers of the Optus network and exceeded the preset safety levels on key routers. Unable to handle the overload, these routers disconnected from the Optus IP Core network to protect themselves.

This was seen as an incident where routing updates sent between external parties had crashed individual routers. For example, a simple typo in a “route map” when redistributed between internal networks can similarly overload routers.

Python in One Easy Lesson

Wed, 01 Nov 2023 04:09:39 +0000

Table of Contents Link to heading

Introduction Link to heading

Python is one of the most widely used programming languages today, known for its simplicity and powerful capabilities. It allows developers to write clean and expressive code with ease, even though it may trade speed for flexibility. Python is distributed open-source, meaning anyone can download and use it freely. The primary hub for Python resources is python.org.

Hot Standby Router Protocol - HSRP

Mon, 09 Oct 2023 00:00:00 +0000

Table of Contents Link to heading

First Hop Redundancy Protocols - FHRPs Link to heading

Info

Hot Standby Router Protocol - HSRP Link to heading

Cisco Proprietary (1994)
It has two versions (v1 & v2)
Hello interval 3 sec
Hold interval 10 sec
It uses UDP port number 1985
It sends multicast hellos via 224.0.0.2 (v1) and 224.0.0.102 (v2)
It support groups numbers from 0 to 255 (v1) and 0 to 4095 (v2)
HSRP virtual MAC 0000.0c07.acxx (XX is group ID) (v1) and 0000.0C9F.Fxxx (v2)
Default Priority is 100
Default Preempt Disable
Default decrement in priority using track 10
It supports two types of authentication (MD-5 & Txt).
It has built in track command

The active router sources hello packets from its configured IP address and the HSRP virtual MAC address while the standby router sources hellos from its configured IP address and the interface MAC address (BIA).

Story Points

Tue, 29 Aug 2023 03:47:07 +0000

A story point is a unit of measure used by Scrum teams to estimate the effort required to complete a user story. Story points are relative, rather than absolute, measures of effort. This means that the effort required to complete one story point’s worth of work may vary from team to team or even from sprint to sprint within the same team. Story points are used to help teams plan and track their progress during a sprint.

Scrum Guide Notes

Wed, 23 Aug 2023 00:00:00 +0000

Table of Contents Link to heading

Link to Scrum Guide Link to heading

Dynamic Host Configuration Protocol - DHCP

Thu, 08 Jun 2023 00:00:00 +0000

Table of Contents Link to heading

Dynamic Host Configuration Protocol (DHCP) Link to heading

Info

A client/server protocol, based on the Bootstrap Protocol (BOOTP), that automatically provides a host with its IP address and other related configuration information such as the subnet mask, default gateway, DNS servers, domain names, and more.

DHCP provides the following advantages:

OSI Application Layer

Thu, 08 Jun 2023 00:00:00 +0000

Table of Contents Link to heading

OSI Application Layer Link to heading

Info

The OSI application layer provides a user interface for network services and applications.

This layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside the OSI model. The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronises cooperating applications, and establishes agreement on procedures for error recovery and control of data integrity.

Special Directories and Files

Fri, 05 May 2023 00:00:00 +0000

Table of Contents Link to heading

Setuid Link to heading

When setuid permission is set on an executable binary file (a program), the binary file is run as the owner of the file, not as the user who executed it.

Ownership and Permissions

Fri, 28 Apr 2023 00:00:00 +0000

Table of Contents Link to heading

File Ownership Link to heading

By default, users own the files that they create, and this ownership can only be changed with administrative privileges.

Creating Users and Groups

Mon, 24 Apr 2023 00:00:00 +0000

Table of Contents Link to heading

User Private Group (UPG) Link to heading

a group account created automatically for a new user account. The group and username would be the same, and the only member of this new group would be the new user.

System and User Security

Thu, 20 Apr 2023 00:00:00 +0000

Table of Contents Link to heading

User Accounts and Groups Link to heading

User accounts designed to provide security since each person on the system must log in using a user account which either allows the person to access specific files and directories or disallows such access, accomplished using file permissions.

Process and Memory Management

Mon, 17 Apr 2023 00:00:00 +0000

Table of Contents Link to heading

Linux Kernel Link to heading

Via a shell, the kernel accepts commands from the user and manages the processes that carry out those commands by giving them access to devices, such as memory, disks, network interfaces, keyboards, mice, and monitors.

Filesystem Hierarchy Standard - FHS

Sat, 15 Apr 2023 00:00:00 +0000

Table of Contents Link to heading

Filesystem Hierarchy Standard (FHS) Link to heading

a set of standards that provides a guideline for Linux distributions on how to organise large numbers of files on the filesystem.

Archiving and Compression

Thu, 06 Apr 2023 00:00:00 +0000

Table of Contents Link to heading

Compression Link to heading

reduces the amount of data needed to store or transmit a file while storing it in such a way that the file can be restored.

Managing Files and Directories

Sat, 01 Apr 2023 00:00:00 +0000

Table of Contents Link to heading

Globbing Link to heading

the process of using wildcards (glob characters) to specify patterns that match sets of filenames.

Enterprise Internet Connectivity

Tue, 28 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Enterprise Connectivity Requirements Link to heading

Outbound
- One-way connectivity from clients to the Internet.
- Private IPv4 addresses with Network Address Translation (NAT) are used for IPv4 connections, allowing clients on a private network to communicate with servers on the public Internet.
- This is a typical home or company LAN end-user model.
Inbound
- Two-way connectivity where external clients can access the enterprise’s internal resources.
- Both public and private IPv4 address space is needed, and so are routing and security considerations.
- This is a typical public server model.

Redundancy for Enterprise Network to ISP Connectivity Link to heading

Edge device redundancy
- Deploying redundant routers protects the network against device failure.
- If one router fails, the redundant router will take its place and Internet connectivity can still be established.
Link redundancy
- Deploying redundant links protects the network against link failure between the router and the ISP router.
ISP redundancy
- If hosting important servers or accessing mission-critical services on the Internet, it is best to have two redundant ISPs.

Single-router Single-homed Link to heading

provides a minimal degree of the ISP connectivity’s resiliency due to no levels of redundancy for hardware, links, or ISPs.

OSPF Routing Protocol

Tue, 28 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Open Short Path First (OSPF) Link to heading

Info

a popular, standards-based IGP, link-state routing protocol, designed to address the limitations of RIP.

OSPF propagates link-state advertisements (LSAs) rather than routing table updates (like DVRPs), which means OSPF networks converge faster than DVRPs.

Basic Scripting

Mon, 27 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Shell Script Link to heading

a file of executable commands stored in a text file.

Network Time Protocol - NTP

Mon, 27 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

System Clock Link to heading

The system clock can be set with:

Dynamic Routing Protocols

Wed, 22 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Dynamic Routing Protocols Link to heading

Read at .

Working With Text

Wed, 22 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Text Files Link to heading

only contain text, no formatting features compared to a word processing file.

Static Routing

Sat, 18 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Static Routing Link to heading

Tip

Read at .

Static versus Dynamic Routing Link to heading

Tip

Read at .

Types of Static Routes Link to heading

There are a few different types of static routes, each with different purposes:

Layer 2/3 Boundary in Lan Hierarchy

Thu, 16 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Layer 2/3 Breakdown Link to heading

Each link between a Layer 3 (L3) device is considered its own network, with each side of the link having its own IP address.
Access layer typically operates over Layer 2 (L2) only, separating ports into different VLANs.
Access layer connects with Distribution layer via the use of trunk ports, which allows multiple different VLANs to traverse the Access/Distribution layer links.
Distribution layer typically has a different network per VLAN.

Inter-VLAN Routing

Sun, 12 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Inter-VLAN Routing Link to heading

VLANs are used to segment switched Layer 2 networks for a variety of reasons. Regardless of the reason, hosts in one VLAN cannot communicate with hosts in another VLAN unless there is a router or a multilayer switch (MLS - switch with Layer-3/Routing capabilities) to provide routing services.

Network Design Factors

Sun, 12 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Key Design Principles Link to heading

Follow these key design principles to serve as the basis for developing network designs.

Understanding Computer Hardware

Sun, 12 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Motherboards Link to heading

or system board, is the main hardware board in the computer through which the central processing unit (CPU), random-access memory (RAM), and other components are all connected.

IP Routing

Fri, 10 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Router Link to heading

Info

An intermediary device that forwards packets among networks and on the Internet.

It has a CPU, DRAM, and storage (ROM, NVRAM, Flash, Hard Drive/USB).
It requires configuration on interfaces before it can be used.
Each interface is on its own network (assigned unique IP addressing information).
- Serial DCE ends must be given a clock rate.
No two interfaces can be on the same network as the router will prevent this from happening.
A router’s purpose include:
- Interconnecting networks, allowing you to visit other remote networks from your own local network.
- Forwarding packets not destined to themselves (unlike hosts).
- Determining the best path to send packets.
- Encapsulating according to the medium’s data link frame type, in the case of a serial link: point-to-point, High Level Data Link Control (HDLC), or other protocols.
  - A switch does not perform these complex tasks.
A router is often the default gateway for a network.
- All hosts on a network should have a default gateway.
- The host will consult with its default gateway when it requires to go to a separate network.

Routing Link to heading

Info

The process a router performs when making forwarding decisions for each packet arriving at its gateway interface.

To forward a packet to a destination network, the router requires a route to that network.
If a route to a destination network does not exist on the router, the packet will be forwarded to a default gateway.
If no default gateway is configured, the packet will be discarded.
The destination network can be a number of routers or hops away from the gateway.
If the router has an entry for the network in its routing table, it would only indicate the next-hop router to which the packet is to be forwarded, not the exact route to the final router.
The routing process uses a routing table to map the destination network address to the next hop and then forwards the packet to this next-hop address.

Routing Table Link to heading

Info

An area of a router’s memory that stores the route forwarding information, such as destination network, next hop, and associated metrics.

Lists IP address groupings, called IP networks and IP subnets.
Consists of a list of prefixes (network address) and their associated prefix length (subnet mask).
- e.g. 10.0.55.0/24.
Displayed using the command show ip route.

Learning Sources Link to heading

A routing table can be populated via three basic sources:

Navigating the Filesystem

Sun, 05 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Introduction Link to heading

In Linux, everything is stored in files.
Files are used to store data such as text, graphics, and programs.
Directories (or folders for Windows and MAC OS X users) are a type of file used to store other files.
The data that they hold are the names of the files that have been entered into them, along with the inode number (a unique identifier number assigned to each file) for where the data for that file exists on the disk.
Directories are used to provide a hierarchical organisation structure.

Directory Structure Link to heading

On a Windows system, the top-level of the directory structure is called My Computer.

Spanning Tree Protocol - STP

Sun, 05 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Spanning Tree Versions Link to heading

802.1D – original specification
- Good for learning, a single spanning tree is used.
- Often called Common Spanning Tree (CST) and STP.
Per-VLAN Spanning Tree (PVST)
- Uses the Cisco proprietary ISL trunking protocol.
  - Inter-Switch Link (ISL) – a way of tagging like 802.1Q.
- Each VLAN has an instance of spanning tree.
- Ability to load balance traffic at L2.
- Includes extensions BackboneFast, UplinkFast, and PortFast.
Per-VLAN Spanning Tree Plus (PVST+)
- Supports ISL and IEEE 802.1Q trunking.
- Supports Cisco proprietary STP extensions.
- Adds BPDU guard and root guard enhancements.
- Root switch selection is done for each VLAN.
- Generally unusable in mixed vendor environments.
802.1W Rapid Per-VLAN Spanning Tree Plus (RPVST+)
- Has faster convergence than 802.1D.
- Root switch selection is done for each VLAN.
- Use RPVST+ if STP is required since it provides for faster convergence than traditional 802.1D default timers.
802.1W Rapid Spanning Tree Protocol (RSTP)
- Introduced in 1982 and provides faster convergence than 802.1D.
- The replacement for CST/STP (IEEE 802.1D), which also provides backwards compatibility.
- Implements generic versions of the Cisco-proprietary STP extensions.
- IEEE has incorporated RSTP into 802.1D, identifying the specification as IEEE 802.1D-2004.
802.1S Multiple Spanning Tree (MST)
- Inspired by the Cisco’s Multiple Instances Spanning Tree Protocol (MISTP).
- IEEE 802.1Q (2003) now includes MST.
- Multiple VLANs can be mapped to the same spanning-tree instance.
- Root switch selection is based on instances.
- Generally unusable in mixed vendor environments.

Name	Based on STP or RSTP?	# Trees	Original IEEE Standard	Config Parameter
STP	STP	1 (CST)	802.1D	N/A
PVST+	STP	1/VLAN	802.1D	pvst
RSTP	RSTP	1 (CST)	802.1w	N/A
Rapid PVST+	RSTP	1/VLAN	802.1w	rapid-pvst
MSTP	RSTP	1 or more*	802.1s	mst

Spanning Tree Protocol (STP) Link to heading

Info

STP ensures a loop-free topology (thus allowing for redundant links) with only one active path between all destinations on the network at any one time.

Without STP, redundancy in the switched network, albeit useful for network reliability, would introduce the following LAN issues:

Server Placement

Sat, 04 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Hierarchical Network Design Link to heading

Read more at

Getting Help

Fri, 03 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Man Pages Link to heading

or manual pages, provide a basic description of the purpose of the command/program/system files, as well as details regarding available options.

Network Hardware

Fri, 03 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Functions of Switches and Routers Link to heading

According to the OSI Layer Model:

VLANs

Fri, 03 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Virtual Local Area Network (VLAN) Link to heading

Info

A logical grouping of network devices in the same broadcast domain or subnet that can span multiple physical segments.

A port (interface) on a switch, or simply a switch port, with only a singular VLAN configured on it is called an access port.
- Access ports are most often used to connect host devices, such as computers and printers. By default on Cisco switches, all switch ports are access ports.
With VLAN, remember that just because two computers are physically connected to the same switch does not mean that they can communicate. VLANs contain/isolate broadcast traffic, where you need a router to move traffic between VLANs.
If multiple VLANs are configured, each must be associated with a unique subnet or network ID.
VLANs helps to:
- Make it easy for network administrators to partition a single switched network to match the functional and security requirements of their systems without having to run new cables or make major changes in their current network infrastructure.
- Isolate broadcasts, multicasts, and unicasts in the individual VLAN.
- Set up by larger businesses to re-partition devices for better traffic management.
- Improve the overall performance of a network by grouping together devices that communicate most frequently or separating different types of traffic.
- Make implementing security policies easier by allowing a higher degree of control over which devices have access to each other.
- Provide additional security since traffic must traverse a L3 device to move between VLAN, where access control list can be implemented to filter traffic.
- Save computing resources and bandwidth with smaller broadcast domains.

Benefit	Description
Simpler management	Similar groups will need similar applications and other network resources
Improved security	Only users in the same VLAN can communicate together
Improved IT efficiency	VLANs can group devices with similar requirements, e.g. faculty vs. students
Reduced Cost	One switch can support multiple groups or VLANs
Better performance	Small broadcast domains reduce traffic, improving bandwidth
Smaller broadcast domains	Dividing the LAN reduces the number of broadcast domains

Types of VLANs Link to heading

Data (or user) VLAN
- Configured to carry only date (user-generated) traffic.
- Not used for carrying management or voice traffic.
- Divides the whole network into 2 groups: one group of users and one group of devices.
Default VLAN
- All switch ports are members of the default VLAN (and therefore parts of the same broadcast domain) when the switch is reset to factory defaults.
- It is the default for management, data, and native VLANs.
- VLAN 1 is the default VLAN for Cisco switches and cannot be renamed or deleted.
Black Hole (or dead-end) VLAN
- Comprises all unused switch ports - not used for anything on the network
  - so that any unauthorised device connecting to an unused switch port will be prevented from communicating beyond the switch to which it is connected.
- Does not have DHCP, Inter-VLAN routing, or device management enabled. This keeps the other VLANs more secure.
Native VLAN
- Serves as a common identifier on opposing ends of a IEEE 802.1Q trunk link.
- Supports traffic coming from many VLANs (tagged traffic) as well as traffic that does not come from a VLAN (untagged traffic).
- Only one native VLAN can be assigned to a trunk port.
- All untagged traffic received on this port will become a member of the native VLAN.
- Frames belonging to the native VLAN are not tagged when being sent out a trunk port.
- Native VLANs pose a security risk, allowing an attacker to hop to another VLAN by double-tagging a frame.
  - Read more at .
Management VLAN
- Used to remotely manage, control, and monitor the devices in your network using Telnet, SSH, SNMP, syslog, or Cisco’s FindIT.
- Should never be carried with user data traffic.
- To communicate remotely with a Cisco switch for management purposes, the switch must have an IP address configured on the management VLAN.
- When all management traffic is on a separate VLAN, it is much harder for unauthorised users to make changes to your network or monitor network traffic.
- The VLAN number is the SVI number on the L2 Switch.
Voice VLAN
- Configured to carry IP voice (Voice over IP - VoIP) traffic from an IP phone.
- Must be separated from other traffic since voice traffic needs:
  - Guaranteed bandwidth,
  - High Quality of Service (QoS) priority,
  - Less than 150ms delay from sender to receiver,
  - Ability to avoid congestion.
- Modern networks must be built around supporting low-latency, high priority voice traffic.

VLAN Trunk Link to heading

Info

An Ethernet point-to-point link between an Ethernet switch interface and an Ethernet interface on another networking device, such as a router or a switch, carrying the traffic of multiple VLANs over a singular link.

A VLAN trunk does not belong to a specific VLAN; rather, it serves as a conduit for VLANs between switches.
Trunks are able to:
- Carry more than one VLAN,
- Extend the VLANs across an entire network,
- Support all VLANs by default,
- Tag frames using the IEEE 802.1Q protocol (dot1q).
An example of trunking usage is a DHCP server, since it might need to assign IP addresses to users across multiple VLANs.

The example below shows a small switched network with a trunk link between S1 and S2 carrying multiple VLAN traffic.

Command-line Skills

Thu, 02 Mar 2023 00:00:00 +0000

Table of Contents Link to heading

Command-Line Interface Link to heading

The Linux community promotes the CLI due to its power, speed and ability to accomplish a vast array of tasks with a single command-line instruction.
The CLI provides more precise control, greater speed and the ability to automate tasks more easily through scripting.
By learning the CLI, a user can easily be productive almost instantly on any flavour or distribution of Linux.

The Shell Link to heading

Once a user has entered a command, the terminal then accepts what the user has typed and passes to a shell.
The shell is the command-line interpreter that translates commands entered by a user into actions to be performed by the operating system.
The Linux environment allows the use of many different shells.
- The most commonly used shell for Linux distributions is called the Bash shell.
The Bash shell also has many popular features, a few of which are:
- Command-line history
- Inline editing
- Scripting
  - The ability to place commands in a file and then interpret (effectively use Bash to execute the contents of) the file, resulting in all of the commands being executed.
- Aliases
  - The ability to create a shortcut that references a command.
- Variables
  - Used to store information for the Bash shell and for the user.
When a terminal application is run, a shell appears displaying an important part of the interface — the prompt.
- Typically the prompt contains information about the user and the system.
- The prompt shown contains the following information:
  - Username (sysadmin)
  - System name (localhost)
  - Current Directory (~) - The ~ symbol is used as shorthand for the user’s home directory.

Switching Security

Mon, 27 Feb 2023 00:00:00 +0000

Table of Contents Link to heading

Media Access Control (MAC) Address Flooding Link to heading

A MAC address a standardised Data Link Layer address that is required for every port of devices that connect to a LAN. Other devices in the network use these addresses to locate specific ports in the network and to create and update routing tables and data structures. MAC addresses are 6 bytes long and are controlled by the IEEE.

Hierarchical Network Design

Sun, 26 Feb 2023 00:00:00 +0000

Table of Contents Link to heading

Flat Model Link to heading

All devices are connected to a single switch instead of separate ones.

Switching Basics

Sun, 26 Feb 2023 00:00:00 +0000

Table of Contents Link to heading

Switching Basics Link to heading

Info

A switch receives a frame into an interface (ingress), then sends the frame out to another interface and eventually exits the interface (egress).

A switch:

The PPDIOO Life Cycle

Sat, 25 Feb 2023 00:00:00 +0000

Table of Contents Link to heading

Life Cycle Approach Link to heading

provides several key benefits aside from keeping the design process organised.

Open-Source Software and Licensing

Fri, 24 Feb 2023 00:00:00 +0000

Table of Contents Link to heading

Open Source Philosophy Link to heading

Philosophy that users have the right to obtain the software source code and modify it for their own use.

Working in Linux

Fri, 24 Feb 2023 00:00:00 +0000

Table of Contents Link to heading

Getting to the Command Line Link to heading

The command-line interface (CLI) is a simple text input system for entering anything from single-word commands to complicated scripts.

Operating Systems

Thu, 23 Feb 2023 00:00:00 +0000

Table of Contents Link to heading

Introduction
Decision Points
Microsoft Windows
Apple macOS
Linux
Linux Distributions
- Red Hat
- SUSE
- Debian
- Android
- Others

Introduction Link to heading

Software that runs on a computing device and manages the hardware and software components that make up the system.

Introduction to Linux

Wed, 22 Feb 2023 00:00:00 +0000

Table of Contents Link to heading

Linux Operating System Link to heading

a combination of software called GNU/Linux which defines the> operating system.

Cryptography

Mon, 01 Aug 2022 00:00:00 +0000

Table of Contents Link to heading

Cryptography sits in between confidentiality and integrity, according to the CIA triad.

Reconnaissance

Mon, 01 Aug 2022 00:00:00 +0000

Table of Contents Link to heading

Reconnaissance Link to heading

(recon) a preliminary survey to gather information about a target.

Risk Based Management Systems

Mon, 01 Aug 2022 00:00:00 +0000

Table of Contents Link to heading

Risk Management Definition Link to heading

Info

Risk management is the process of identifying risk, assessing risk, and taking steps to reduce risk to an acceptable level.

The risk management approach determines the processes, techniques, tools, and team roles and responsibilities for a business.

CIA Triad

Mon, 25 Jul 2022 00:00:00 +0000

Table of Contents Link to heading

The CIA Triad Link to heading

Info

A security model of confidentiality, integrity and availability designed to guide policies for information security within an organisation.

Used when we want to protect a network and the data contained within it.

Concepts

Mon, 25 Jul 2022 00:00:00 +0000

Table of Contents Link to heading

Business Resilience Definition Link to heading

Info

Resilience is the ability to survive, adapt, and flourish in the face of turbulent change.

Info

Business resilience is the ability of a business to withstand, adapt and thrive in the face of turbulent change that originates from both internal and external sources as well as anticipated or unanticipated events.

A resilient business can adapt to disruptions and keep operating while looking after its people, assets, and brand equity.

Views

Mon, 04 Apr 2022 00:00:00 +0000

Table of Contents Link to heading

Database views Link to heading

Views are very useful for complex queries Queries with lots of joins Queries with complex conditions (e.g. aggregates) Especially if the queries are used frequently

Control Statements

Tue, 29 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Why control statement Link to heading

Control statements allow actions to happen depending on a condition.

Common Functions

Mon, 28 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

What is a Function Link to heading

Functions are calculations performed by the Database Management System (DBMS).

Aggregate Functions

Tue, 22 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Aggregate Queries Link to heading

Aggregate queries or aggregation is a method of performing computations over sets of numerical values in multiple tuples of a relation and returning a single value.

Set Operators

Mon, 21 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Example Database Link to heading

The below two relations will be used as examples for this post.

Nested Queries

Wed, 16 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Table Joins

Tue, 15 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

`JOIN` keyword Link to heading

Tables (relations) can be combined to form a new relation using the JOIN keyword.

Query Writing

Mon, 14 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Why Query Link to heading

Now that we have got our tables storing data (records), let’s start asking questions (queries) about those data.

Data Manipulation

Fri, 11 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Data Manipulation Link to heading

So we have created a set of tables. However:

Table Constraints

Thu, 10 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Definition Link to heading

Constraints are clauses that need to be satisfied by data in the database.

Physical Design

Wed, 09 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Introduction Link to heading

After the conceptual design and the physical design, the next phase is to take the relational schemas and implement them using a DBMS.

Logical Design

Tue, 08 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Introduction Link to heading

After the conceptual design, the next phase is to create functional relational schemas based on the conceptual design.

Conceptual Design

Mon, 07 Mar 2022 00:00:00 +0000

Table of Contents Link to heading

Conceptual Modelling Link to heading

Overall, Database requirements are collected and visualised as a UML diagram.

Normalisation

Sat, 26 Feb 2022 00:00:00 +0000

Table of Contents Link to heading

Good and Bad Database Designs Link to heading

When designing a database, people tend to do one that captures all or too much of the required information.

Identify the Primary Key

Fri, 25 Feb 2022 00:00:00 +0000

Table of Contents Link to heading

Introduction Link to heading

Picking a good Primary Key from a list of available Candidate Keys might be an unappealing process, but try to stick to these rules to make your life easier.

Key Concepts

Thu, 24 Feb 2022 00:00:00 +0000

Table of Contents Link to heading

What Is A Key Link to heading

A KEY in the DBMS is a set of one or more attributes whose values can uniquely identify a given tuple within a relation.

Relational Concepts

Wed, 23 Feb 2022 00:00:00 +0000

Table of Contents Link to heading

General Terminology Link to heading

Relational Name	Common Name	Alternative
relation	table	-
attribute	column	field
tuple	row	record

Within a table, every column name must be UNIQUE.

Why Database?

Tue, 22 Feb 2022 00:00:00 +0000

Table of Contents Link to heading

Traditional And Physical Data Storage Link to heading

Limited by physical size
Limited multi-access - a borrowed book can only be viewed by one person at a time.
Limited search methods (title, author, subject)
Slow turn-around
Multiple indexes that must be rigorously maintained.
Complex Query Limitations - vast amounts of time wasted counting the number of books on a subject or by an author.
Anomalies: - What IFs:

A card is misplaced?
A catalogue card is misplaced?
An item is entered into / deleted in one index but not the others?

Image Source: Britannica

Fundamentals

Mon, 21 Feb 2022 00:00:00 +0000

Table of Contents Link to heading

What Is A Database Link to heading

A collection of tables containing data that are used to retrieve information.

Port Addressing

Sun, 28 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Port Numbers Link to heading

Info

Allow you to track multiple conversations generated by the same host using the same IP address.

The Need for Port Addressing Link to heading

Info

To keep track of the various applications that are communicating, the transport layer assigns a source and a destination port numbers to the segment header to allow the computers to distinguish between different types of data communication and direct them to the appropriate destination.

Socket Link to heading

Info

The unique combination of a L4 port number and a L3 IP address assigned to a host that track a particular session.

A socket pair, consisting of the source and destination IP addresses and port numbers, is also unique and identifies the session between the two hosts.

OSI Transport Layer

Sat, 27 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Tip

The terms client and server are used as a reference for simplicity, but the communication process can be initiated by any two hosts.

OSI Transport Layer Link to heading

Info

The OSI transport layer is responsible for dividing and managing communications between the processes running in the two end systems.

Tip

Enable multiple applications to communicate over the network at the same time and manage the individual traffic streams over a single link.
Ensure that, if required, all the data is received reliably and in order by the correct application.

Perspectives of Other Layers Link to heading

Applications do not need to know the operational details of the network in use. The applications generate data that is sent from one application to another, without regard to the destination host type, the type of media over which the data must travel, the path taken by the data, the congestion on a link, or the size of the network.

Network Address Translation - NAT

Mon, 22 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Network Address Translation (NAT) Link to heading

Info

NAT, defined in RFC 3022, allows a host using private addresses to communicate with other hosts through the Internet by translating the private address into the valid, registered, globally unique IP address.

Operation Link to heading

A host is using a private IP address is trying to communicate with a server on the Internet using a public IP address.

Internet Control Message Protocol - ICMP

Sun, 21 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Internet Control Message Protocol (ICMP) Link to heading

Info

Ping (Packet Internet Groper) uses ICMP to send an ICMP echo request to another IP address. The computer with that IP address should reply with an ICMP echo reply. If that works, you successfully have tested the IP network.

ICMP Message Encapsulation Link to heading

Info

ICMP packets are delivered using the IP protocol and encapsulated into datagrams in the same way that any other data is delivered using IP.

The encapsulation of an ICMP packet within the IP packet datagram data area is as follows:

Subnetting and Supernetting

Fri, 19 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Subnet or Subnetwork Link to heading

Info

A logical subdivision of an IP network.

Subnetting Link to heading

Info

The method of dividing full network address classes into smaller pieces.

Complete IP address exhaustion has been prevented.
Network traffic can travel a shorter distance without passing through unnecessary routers to reach its destination.

Subnet Mask Link to heading

Info

The number of bits of the network part of the IP address.

255.255.255.0 in bits is equal to 11111111.11111111.11111111.00000000
The zeros are host bits, the ones are network bits.

CIDR Prefix or Prefix Length Link to heading

Info

Equivalent to the number of ones in the subnet mask in binary, represented as a slash followed by a number that represents the number of bits in the prefix.

Subnet Mask	CIDR Prefix
0.0.0.0	/0
128.0.0.0	/1
192.0.0.0	/2
224.0.0.0	/3
240.0.0.0	/4
248.0.0.0	/5
252.0.0.0	/6
254.0.0.0	/7
255.0.0.0	/8
255.128.0.0	/9
255.192.0.0	/10
255.224.0.0	/11
255.240.0.0	/12
255.248.0.0	/13
255.252.0.0	/14
255.254.0.0	/15
255.255.0.0	/16
255.255.128.0	/17
255.255.192.0	/18
255.255.224.0	/19
255.255.240.0	/20
255.255.248.0	/21
255.255.252.0	/22
255.255.254.0	/23
255.255.255.0	/24
255.255.255.128	/25
255.255.255.192	/26
255.255.255.224	/27
255.255.255.240	/28
255.255.255.248	/29
255.255.255.252	/30
255.255.255.254	/31
255.255.255.255	/32

Borrowing Host Bits Link to heading

Info

For every borrowed host bit, the network size is split in half, thereby doubling the number of subnets and halving the maximum number of addresses per subnet.

CIDR Prefix	# IP Addresses = 2ⁿ	# Usable IP Addresses = 2ⁿ-2
/32	1	1
/31	2	2*
/30	4	2
/29	8	6
/28	16	14
/27	32	30
/26	64	62
/25	128	126
/24	256	254
/23	512	510
/22	1024	1022
/21	2048	2046
/20	4096	4094
/19	8192	8190
/18	16,384	16,382
/17	32,768	32,766
/16	65,536	65,534
/15	131,072	131,070
/14	262,144	262,142
/13	524,288	524,286
/12	1,048,576	1,048,574
/11	2,097,152	2,097,150
/10	4,194,304	4,194,302
/9	8,388,608	8,388,606
/8	16,777,216	16,777,214
/7	33,554,432	33,554,430
/6	67,108,864	67,108,862
/5	134,217,728	134,217,726
/4	268,435,456	268,435,454
/3	536,870,912	536,870,910
/2	1,073,741,824	1,073,741,822
/1	2,147,483,648	2,147,483,646

/31 Networks Link to heading

Info

The use of /31 networks is a special case defined by RFC 3021 where the two IP addresses in the subnet are usable for point-to-point links to conserve IPv4 address space.

On systems that do not support RFC 3021, the subnet is unusable because the only two addresses provided by the subnet mask are reserved: one for the network address and the other for the broadcast address; therefore, there is no usable host addresses.

Binary - Base 2

Thu, 18 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Binary Numbering Link to heading

All computer data is represented using the binary number system.

Internet Protocol - IP

Wed, 17 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Internet Protocol (IP) Link to heading

Info

designed as a protocol with low overhead, providing only the functions that are necessary to deliver a packet from a source to a destination over an interconnected system of networks.

IP was not designed to track and manage the flow of packets. These functions, if required, are performed by other protocols at other layers, primarily TCP at L4.

OSI Network Layer

Tue, 16 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Tip

A host refers to a device that is in an IP network and has an IP address.

OSI Network Layer Link to heading

Info

The OSI network layer prepares transport layer segments for routing from one host to another.

Note

Assign logical addresses to devices on the network
Encapsulate the packet with necessary data for delivery
Fragment the packet when it comes across a network that restricts the size of the packet
Route the packet from the source to the destination through the web of connected networks
Have the data decapsulated for processing by the destination host

The network layer receives segments (L4 PDU), which have been processed into a transportable size and numbered for reliability, from the transport layer. It is now up to the network layer to use protocols to add addressing and other information to the PDU and send it (L3 PDU) to the next router along the best route to the destination network.

Link Aggregation - EtherChannel

Thu, 11 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Link Aggregation
Mode Pairs
- PAgP
- LACP

Link Aggregation Link to heading

the process of grouping multiple physical interfaces (ports) into one logical channel.

Discovery Protocols

Wed, 10 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Discovery Protocol Link to heading

Info

A discovery protocol is used by network devices to advertise their identity and capabilities to other devices and receive the information from a directly connected Layer 2 device - called a neighbour.

Neighbouring information shows the ID/IP address of devices, types of devices connected, the router interfaces they are connected to, the interfaces used to make the connections, and the model numbers of the devices.

Address Resolution Protocol - ARP

Tue, 09 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Address Resolution Protocol (ARP) Link to heading

Info

ARP is used to translate 48-bit MAC addresses into 32-bit IPv4 addresses in IPv4 LANs.

Being ARP enabled, a host or router can dynamically learn the MAC address of another IP host or router on the same LAN.

Hexadecimal - Base 16

Mon, 08 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Hexadecimal (Hex) Numbering Link to heading

a convenient way to represent binary values.

Ethernet LAN Switching

Sun, 07 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Switch Fundamentals Link to heading

The switch makes its forwarding decisions based solely on the L2 MAC addresses and is completely unaware of the L3 protocol being carried in the data portion of the frame, such as an IPv4 packet, an ARP message, or an IPv6 ND packet.

Media Access Control (MAC) Address

Sat, 06 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

MAC Address Table or Content-Addressable Memory (CAM) Table Link to heading

Info

A database stored in the RAM of a switch that maps destination MAC addresses with the ports used to connect to each node.

RAM is a type of volatile memory that can be accessed quickly by the switch. It is also where the switch stores its running configuration, routing tables, ARP tables, and other temporary data.

OSI Data Link Layer

Fri, 05 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

Tip

A node refers to a device communicating at this layer.

OSI Data Link Layer Link to heading

For packets to be transported from source host to destination host, they must traverse different physical networks (e.g., copper wires, microwaves, optical fibers, and satellite links), but network layer packets do not have a way to directly access these different media.

OSI Physical Layer

Mon, 01 Nov 2021 00:00:00 +0000

Table of Contents Link to heading

OSI Physical Layer Link to heading

Info

The OSI physical layer encodes the binary digits that represent L2 frames into signals and to transmit and receive these signals across the physical media (e.g., copper wires, optical fibre, and wireless) that connect network devices.

The data-link frame that comes down to the physical layer contains a string of bits representing application, presentation, session, transport, and network information.

Network Addressing

Thu, 28 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Logical versus Physical Addresses Link to heading

The data link and network layers are both responsible for delivering the data from the source host to the destination host.

OSI Reference Model

Wed, 27 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Layered Model Link to heading

Notei

Read at .

OSI Reference Model Link to heading

Info

provides an abstract description of the network communication process.

It was developed by the International Organisation for Standardisation (ISO) to provide a road map for non-proprietary protocol development.

TCP/IP Protocol Model

Tue, 26 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Protocols Link to heading

predetermined rules that govern all communications over a network.

Rules of Communication

Mon, 25 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Communication Fundamentals Link to heading

A network can be as complex as devices connected across the Internet, or as simple as two computers directly connected to one another with a single cable, and anything in-between. Networks can vary in size, shape, and function. However, simply having a wired or wireless physical connection between end devices is not enough to enable communication. For communication to occur, devices must know “how” to communicate.

Reliable Network

Thu, 14 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Network Architecture Link to heading

the technologies that support the infrastructure and the programmed services and rules, or protocols, that move data across the network.

LANs, WANs, and the Internet

Wed, 13 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Network Infrastructure Link to heading

varies greatly in terms of:

Network Components

Tue, 12 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Overview Link to heading

The path that a message takes from source to destination can be as simple as a single cable connecting one computer to another, or as complex as a collection of networks that literally spans the globe. This network infrastructure provides the stable and reliable channel over which these communications occur.

Naming Conventions

Mon, 11 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Rules Link to heading

Although you are allowed to make up your own names for variables, you must follow these rules:

Providing Resources in a Network

Mon, 11 Oct 2021 00:00:00 +0000

Table of Contents Link to heading

Network of Many Sizes Link to heading

Networks come in all sizes, ranging from simple networks consisting of two computers to complex ones connecting millions of devices.