Answered some network related questions (bregman-arie#360)

README.md

@@ -2,7 +2,7 @@
 
 :information_source:  This repo contains questions and exercises on various technical topics, sometimes related to DevOps and SRE
 
-:bar_chart:  There are currently **2619** exercises and questions
+:bar_chart:  There are currently **2621** exercises and questions
 
 :warning:  You can use these for preparing for an interview but most of the questions and exercises don't represent an actual interview. Please read [FAQ page](faq.md) for more details
 
@@ -228,6 +228,11 @@ CSMA/CD algorithm:
   * switch
   * hub</summary><br><b>
 
+A router, switch, and hub are all network devices used to connect devices in a local area network (LAN). However, each device operates differently and has its specific use cases. Here is a brief description of each device and the differences between them:
+
+1. Router: is a network device that connects multiple network segments together. It operates at the network layer (Layer 3) of the OSI model and uses routing protocols to direct data between networks. Routers use IP addresses to identify devices and route data packets to the correct destination.
+2. Switch: is a network device that connects multiple devices on a LAN. It operates at the data link layer (Layer 2) of the OSI model and uses MAC addresses to identify devices and direct data packets to the correct destination. Switches allow devices on the same network to communicate with each other more efficiently and can prevent data collisions that can occur when multiple devices send data simultaneously.
+3. Hub: is a network device that connects multiple devices through a single cable and is used to connect multiple devices without segmenting a network. However, unlike a switch, it operates at the physical layer (Layer 1) of the OSI model and simply broadcasts data packets to all devices connected to it, regardless of whether the device is the intended recipient or not. This means that data collisions can occur, and the network's efficiency can suffer as a result. Hubs are generally not used in modern network setups, as switches are more efficient and provide better network performance.
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@@ -334,6 +339,11 @@ Systems keep an ARP look-up table where they store information about what IP add
 
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 <summary>What is TTL? What does it helps to prevent?</summary><br><b>
+
+- TTL (Time to Live) is a value in an IP (Internet Protocol) packet that determines how many hops or routers a packet can travel before it is discarded. Each time a packet is forwarded by a router, the TTL value is decreased by one. When the TTL value reaches zero, the packet is dropped, and an ICMP (Internet Control Message Protocol) message is sent back to the sender indicating that the packet has expired.
+- TTL is used to prevent packets from circulating indefinitely in the network, which can cause congestion and degrade network performance.
+- It also helps prevent packets from being trapped in routing loops, where packets continuously travel between the same set of routers without ever reaching their destination.
+- In addition, TTL can be used to help detect and prevent IP spoofing attacks, where an attacker attempts to impersonate another device on the network by using a false or fake IP address. By limiting the number of hops that a packet can travel, TTL can help prevent packets from being routed to destinations that are not legitimate.
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@@ -351,22 +361,51 @@ Read more [here](https://linuxjourney.com/lesson/dhcp-overview)
 
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 <summary>Can you have two DHCP servers in the same network? How it works?</summary><br><b>
+
+It is possible to have two DHCP servers on the same network, however it is not recommended, and it is important to configure them carefully to prevent conflicts and configuration problems.
+- When two DHCP servers are configured on the same network, there is a risk that both servers will assign IP addresses and other network configuration settings to the same device, which can cause conflicts and connectivity issues. Additionally, if the DHCP servers are configured with different network settings or options, devices on the network may receive conflicting or inconsistent configuration settings.
+- However, in some cases, it may be necessary to have two DHCP servers on the same network, such as in large networks where one DHCP server may not be able to handle all the requests. In such cases, DHCP servers can be configured to serve different IP address ranges or different subnets, so they do not interfere with each other.
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 <summary>What is SSL tunneling? How does it works?</summary><br><b>
+
+- SSL (Secure Sockets Layer) tunneling is a technique used to establish a secure, encrypted connection between two endpoints over an insecure network, such as the internet. The SSL tunnel is created by encapsulating the traffic within an SSL connection, which provides confidentiality, integrity, and authentication.
+
+Here's how SSL tunneling works:
+
+1. A client initiates an SSL connection to a server, which involves a handshake process to establish the SSL session.
+2. Once the SSL session is established, the client and server negotiate encryption parameters, such as the encryption algorithm and key length, and exchange digital certificates to authenticate each other.
+3. The client then sends traffic through the SSL tunnel to the server, which decrypts the traffic and forwards it to its destination.
+4. The server sends traffic back through the SSL tunnel to the client, which decrypts the traffic and forwards it to the application.
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 <summary>What is a socket? Where can you see the list of sockets in your system?</summary><br><b>
+
+- A socket is a software endpoint that enables two-way communication between processes over a network. Sockets provide a standardized interface for network communication, allowing applications to send and receive data across a network. To view the list of open sockets on a Linux system: 
+***netstat -an***
+- This command displays a list of all open sockets, along with their protocol, local address, foreign address, and state.
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 <summary>What is IPv6? Why should we consider using it if we have IPv4?</summary><br><b>
+
+- IPv6 (Internet Protocol version 6) is the latest version of the Internet Protocol (IP), which is used to identify and communicate with devices on a network. IPv6 addresses are 128-bit addresses and are expressed in hexadecimal notation, such as 2001:0db8:85a3:0000:0000:8a2e:0370:7334.
+
+There are several reasons why we should consider using IPv6 over IPv4:
+
+1. Address space: IPv4 has a limited address space, which has been exhausted in many parts of the world. IPv6 provides a much larger address space, allowing for trillions of unique IP addresses..
+2. Security: IPv6 includes built-in support for IPsec, which provides end-to-end encryption and authentication for network traffic.
+3. Performance: IPv6 includes features that can help to improve network performance, such as multicast routing, which allows a single packet to be sent to multiple destinations simultaneously.
+4. Simplified network configuration: IPv6 includes features that can simplify network configuration, such as stateless autoconfiguration, which allows devices to automatically configure their own IPv6 addresses without the need for a DHCP server.
+5. Better mobility support: IPv6 includes features that can improve mobility support, such as Mobile IPv6, which allows devices to maintain their IPv6 addresses as they move between different networks.
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 <summary>What is VLAN?</summary><br><b>
+
+- A VLAN (Virtual Local Area Network) is a logical network that groups together a set of devices on a physical network, regardless of their physical location. VLANs are created by configuring network switches to assign a specific VLAN ID to frames sent by devices connected to a specific port or group of ports on the switch.
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@@ -385,14 +424,28 @@ With IPv6 protocol, it issues a error to the user's computer.
 
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 <summary>True or False?. Ping is using UDP because it doesn't care about reliable connection</summary><br><b>
+
+False. Ping is actually using ICMP (Internet Control Message Protocol) which is a network protocol used to send diagnostic messages and control messages related to network communication.
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 <summary>What is SDN?</summary><br><b>
+
+- SDN stands for Software-Defined Networking. It is an approach to network management that emphasizes the centralization of network control, enabling administrators to manage network behavior through software abstraction.
+- In a traditional network, network devices such as routers, switches, and firewalls are configured and managed individually, using specialized software or command-line interfaces. In contrast, SDN separates the network control plane from the data plane, allowing administrators to manage network behavior through a centralized software controller.
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 <summary>What is ICMP? What is it used for?</summary><br><b>
+
+- ICMP stands for Internet Control Message Protocol. It is a protocol used for diagnostic and control purposes in IP networks. It is part of the Internet Protocol suite, operating at the network layer.
+
+ICMP messages are used for a variety of purposes, including:
+1. Error reporting: ICMP messages are used to report errors that occur in the network, such as a packet that could not be delivered to its destination.
+2. Ping: ICMP is used to send ping messages, which are used to test whether a host or network is reachable and to measure the round-trip time for packets.
+3. Path MTU discovery: ICMP is used to discover the Maximum Transmission Unit (MTU) of a path, which is the largest packet size that can be transmitted without fragmentation.
+4. Traceroute: ICMP is used by the traceroute utility to trace the path that packets take through the network.
+5. Router discovery: ICMP is used to discover the routers on a network.
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@@ -402,10 +455,6 @@ NAT stands for network address translation. It’s a way to map multiple local p
 For example, your computer's private IP could be 192.168.1.100, but your router maps the traffic to it's public IP (e.g. 1.1.1.1). Any device on the internet would see the traffic coming from your public IP (1.1.1.1) instead of your private IP (192.168.1.100).
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-<summary>Which factors affect network performances</summary><br><b>
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 <summary>Which port number is used in each of the following protocols?:
 
@@ -429,6 +478,17 @@ For example, your computer's private IP could be 192.168.1.100, but your router
 
 <details>
 <summary>Which factors affect network performances</summary><br><b>
+
+Several factors can affect network performance, including:
+
+1. Bandwidth: The available bandwidth of a network connection can significantly impact its performance. Networks with limited bandwidth can experience slow data transfer rates, high latency, and poor responsiveness.
+2. Latency: Latency refers to the delay that occurs when data is transmitted from one point in a network to another. High latency can result in slow network performance, especially for real-time applications like video conferencing and online gaming.
+3. Network congestion: When too many devices are using a network at the same time, network congestion can occur, leading to slow data transfer rates and poor network performance.
+4. Packet loss: Packet loss occurs when packets of data are dropped during transmission. This can result in slower network speeds and lower overall network performance.
+5. Network topology: The physical layout of a network, including the placement of switches, routers, and other network devices, can impact network performance.
+6. Network protocol: Different network protocols have different performance characteristics, which can impact network performance. For example, TCP is a reliable protocol that can guarantee the delivery of data, but it can also result in slower performance due to the overhead required for error checking and retransmission.
+7. Network security: Security measures such as firewalls and encryption can impact network performance, especially if they require significant processing power or introduce additional latency.
+8. Distance: The physical distance between devices on a network can impact network performance, especially for wireless networks where signal strength and interference can affect connectivity and data transfer rates.
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