Are both single mode and multi mode cables generally terminated in pairs?

• Internet Explanation: Yes, both single-mode and multi-mode fiber optic cables are generally terminated in pairs. This is because most fiber optic communication is full-duplex, meaning that data can be transmitted in both directions simultaneously. One fiber in the pair is used to transmit data signals, and the other is used to receive them. This is why you'll often see fiber optic cables and connectors referred to as "duplex" (e.g., duplex LC or duplex SC), and why patch cables often have two connectors at each end. However, it's worth noting that there are also "simplex" fiber optic cables and connectors, which consist of a single fiber and are used for applications that only require one-way data transmission. But these are less common than duplex configurations in most networking environments.

What is an FQDN (Fully Qualified Domain Name), and how is it different from a URL?

• Internet Explanation: FQDN stands for Fully Qualified Domain Name. It's a complete and unambiguous domain name that specifies an exact location in the Domain Name System (DNS) hierarchy. This means it includes all higher levels of the DNS structure, not just the host and domain name. An FQDN consists of several parts:
• Hostname: The name assigned to a device connected to a computer network.
• Domain name: The name that represents an organization or entity on the internet.
• Top-level domain (TLD): The highest level of the domain structure (like .com, .org, .net, .gov, etc.)
• For example, in the FQDN "www.example.com": "www" is the hostname "example" is the domain name "com" is the top-level domain
• Internet Explanation Continued: Both FQDN (Fully Qualified Domain Name) and URL (Uniform Resource Locator) are used to find resources on the internet, but they serve different purposes and contain different types of information. FQDN is like the full name of a specific computer or server on the internet. It's used to identify a specific machine in a network. For example, "www.example.com" is an FQDN where "www" is the hostname, "example" is the domain name, and "com" is the top-level domain. URL, on the other hand, is like a full address that tells your web browser exactly where to find a specific resource on the internet. It includes the protocol (like HTTP or HTTPS), the domain name, and often a specific page or file on that domain. For example, "https://www.example.com/homepage.html" is a URL. In this URL: "https" is the protocol, which tells your browser how to access the resource. "www.example.com" is the FQDN, which tells your browser where the server is located. "/homepage.html" is the specific file or page on that server.
• My Explanation: FQDN is the full term for what is commonly referred too simply as a domain name. FQDN is specifically a domain name that includes a hostname (or subdomain), the domain itself, and its top level domain (or TLD). It is designed to point to a specific machine on the network, or more commonly, the internet. For example, patrick.quam.computer would be a FQDN. A URL is a link to a specific resource on a device, and as such the FQDN is part of a url. https://patrick.quam.computer.notes/other is a url, which includes, but is not, a FQDN.

How do single mode and multi mode fiber connect to fiber transceivers? Do the transceivers have sc or lc connectors and you just need to make sure you buy the transceiver for the kind and length of cable you have?

• Internet answer: Most modern transceivers will use LC connectors because they are smaller size. When choosing a transceiver there are 4 main things to consider:
1. The type of fiber optic cable (single-mode or multi-mode) you're using.
2. The data rate that you need to support.
3. The distance the signal needs to travel.
4. The type of connector on your fiber optic cable.
• Other technical considerations when choosing cabling and transceivers:
• Different transceivers operate at different wavelengths, typically 850nm for multi-mode fibers and 1310nm or 1550nm for single-mode fibers. The wavelength is important because it determines the type of light source (LED or laser) and the type of photodetector used in the transceiver.
• The power budget of a fiber optic link is the maximum amount of power loss that a signal can tolerate while still maintaining acceptable signal quality. It's determined by the difference between the minimum transmitter power and the minimum receiver sensitivity. When designing a fiber optic link, you need to ensure that the total power loss (caused by factors such as cable length, connectors, and splices) doesn't exceed the power budget.
• Dispersion is a phenomenon that causes the signal to spread out over time, which can degrade signal quality. Single-mode fibers can suffer from chromatic dispersion, while multi-mode fibers can suffer from modal dispersion. Some types of transceivers use techniques such as dispersion compensation to mitigate the effects of dispersion.

What are chromatic and modal dispersion?

• Chromatic Dispersion: This type of dispersion occurs in single-mode fibers and is caused by the different speeds at which different wavelengths (colors) of light travel through the fiber. In an optical fiber, light doesn't travel at exactly the same speed for all wavelengths. This slight variation can cause different wavelengths to arrive at the receiver at slightly different times, which can cause the signal to spread out or disperse. This is particularly relevant for systems that use multiple wavelengths of light (DWDM systems, for example).
• Modal Dispersion: This type of dispersion occurs in multi-mode fibers. In a multi-mode fiber, light can take multiple paths (or modes) down the fiber, and these different paths can have different lengths. This means that light taking one path might arrive at the receiver before light taking a different path, which can cause the signal to spread out or disperse. This is one of the reasons why multi-mode fibers are typically used for shorter distances.
• Modal Dispersion wikipedia
• Dispersion (optics) wikipedia

How is data physically stored on SSDs?

• Data in a Solid State Drive (SSD) is stored in NAND flash memory chips. These chips are made up of many memory cells, which are the smallest units that can store data. The physical storage of data in these cells is based on the principles of electrical engineering and quantum mechanics.
• Each memory cell in a NAND flash memory chip is essentially a field-effect transistor. It has a control gate and a floating gate, separated by an oxide layer.
• Data is stored in these cells by trapping or removing electrons from the floating gate. When a high voltage is applied to the control gate, electrons in the substrate (the semiconductor material) are given enough energy to cross the oxide layer and get trapped in the floating gate. This process is called "programming" or "writing" data.
• To read the data, a medium voltage is applied to the control gate. This causes a current to flow through the transistor. The amount of current depends on how many electrons are trapped in the floating gate. By measuring this current, the SSD's controller can determine whether a "0" or a "1" is stored in the cell.
• To erase data, a high voltage is applied to the substrate, causing the electrons in the floating gate to gain enough energy to cross the oxide layer and return to the substrate. This process is called "erasing" data.
• Modern SSDs often use multi-level cells (MLCs) or triple-level cells (TLCs) to store more than one bit of data per cell. They do this by trapping different amounts of charge in the floating gate to represent different states. For example, an MLC can store 2 bits of data by using 4 states: no charge, low charge, medium charge, and high charge.
• Branch Education: How do SSDs Work?

What is the difference between a subnet and a vlan?

• More info on subnets and subnet mask here
• Powercert video on Subnets vs VLANs
• Both subnets and VLANs are used to segment and organize networks, but they operate at different layers of the OSI model and serve different purposes.
• Subnets:
• Operate at Layer 3 (Network Layer) of the OSI model.
• Used to segment an IP network into smaller, more manageable IP address ranges. This segmentation is based on IP addresses.
• A subnet is defined by its IP address range and subnet mask (e.g., 192.168.1.0/24).
• Devices within the same subnet can communicate directly with each other.
• Communication between devices in different subnets requires a router or Layer 3 switch.
• Designed to make efficient use of IP address space.
• Creates logical separation of different parts of a network based on IP addressing.
• VLANs:
• Operate at Layer 2 (Data Link Layer) of the OSI model.
• Used to segment a physical network into multiple logical networks, regardless of the IP addresses of the devices. This segmentation is based on switch port membership.
• A VLAN is identified by a VLAN ID (a number between 1 and 4095).
• Devices within the same VLAN can communicate directly with each other at Layer 2.
• Communication between devices in different VLANs requires a Layer 3 device (router or Layer 3 switch) and is known as inter-VLAN routing.
• Designed to enhance security by isolating sensitive devices or departments.
• One of the primary reasons for using VLANs is to limit the scope of broadcast traffic. If a VLAN spans a large area or many devices, it can lead to increased broadcast traffic, potentially affecting network performance.
• Creates logical separation of devices based on function, department, or project, regardless of their physical location or IP address.
• VLANs offer flexibility in grouping devices regardless of their physical location or IP address.
• VLANs can span across multiple subnets, and conversely, multiple VLANs can exist within a single subnet. However, while VLANs spanning multiple subnets can be useful in specific scenarios, they can also introduce management complexity. It's generally easier to manage and troubleshoot networks when there's a clear one-to-one relationship between VLANs and subnets.

What actually happens after your device recieves an IP from DNS?

1. TCP Connection Establishment (Three-Way Handshake):
• The client initiates a connection to the server using the Transmission Control Protocol (TCP), the primary transport protocol of the internet.
• A three-way handshake occurs to establish this connection:
1. SYN: The client sends a SYN (synchronize) packet to the server at the obtained IP address, indicating it wants to establish a connection.
2. SYN-ACK: The server responds with a SYN-ACK (synchronize-acknowledge) packet, acknowledging the client's request.
3. ACK: The client sends an ACK (acknowledge) packet back to the server, completing the handshake and establishing the connection.
2. HTTP/HTTPS Request:
• Once the TCP connection is established, the client sends an HTTP (Hypertext Transfer Protocol) or HTTPS (HTTP Secure) request to the server. This request includes details like the desired webpage, the browser being used, supported data formats, and more.
• If the website uses HTTPS, there's an additional layer of security through SSL/TLS encryption. Before exchanging the main content, an SSL/TLS handshake occurs to agree on encryption methods and exchange cryptographic keys.
3. Server Processing:
• The server processes the client's request. For static websites, this might simply involve fetching the requested webpage. For dynamic websites, the server might need to run scripts, query databases, or perform other operations to generate the requested content.
4. HTTP/HTTPS Response:
• The server sends an HTTP/HTTPS response back to the client. This response includes the requested content (like HTML, CSS, JavaScript, images) and status codes indicating the result of the request (e.g., 200 for "OK", 404 for "Not Found").
5. Rendering the Webpage:
• The client's browser processes the received data, rendering the webpage for the user to view. This involves:
• Parsing the HTML, CSS, and JavaScript.
• Displaying images, videos, and other media.
• Executing any client-side scripts for interactivity.
6. TCP Connection Termination:
• After the data exchange is complete, the TCP connection is terminated to free up resources. This involves a four-step process:
1. FIN: One side (usually the client) sends a FIN (finish) packet, indicating it's done sending data.
2. ACK: The other side acknowledges with an ACK packet.
3. FIN: The other side then sends its own FIN packet.
4. ACK: The first side acknowledges with an ACK packet, completing the termination.
7. Persistent Connections:
• Modern web protocols, like HTTP/2, support persistent connections. Instead of closing the connection after a single request-response cycle, the connection remains open for a set period, allowing multiple requests and responses without the overhead of establishing a new connection each time.

What is IGMP?

• The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers on an IPv4 network to establish multicast group memberships.
• IGMP is used by IP hosts to report their multicast group memberships to any neighboring multicast routers.
• Instead of broadcasting data to all devices or sending multiple unicast streams, multicasting sends data only to the group of devices that are interested in that data.
• IGMP is primarily concerned with managing multicast group memberships at the IP layer (Layer 3 of the OSI model). Its main function is to allow hosts to communicate their interest in joining or leaving a multicast group. The multicast group is identified by a multicast IP address (in the range of 224.0.0.0 to 239.255.255.255 for IPv4).
• While IGMP operates at the IP layer, the actual data frames on a wired Ethernet network (like most LANs) are transmitted using MAC addresses at the Data Link layer (Layer 2). For multicast data to be efficiently delivered on a local network, there's a mapping between multicast IP addresses and multicast MAC addresses.
• Multicasting is more bandwidth-efficient than broadcasting or unicasting for scenarios where the same data needs to be sent to multiple recipients. IGMP ensures that multicast data is only sent to hosts that have explicitly shown interest.
• Common Uses:
• Multicast and IGMP are often used in IPTV and other streaming media applications where the same content is delivered to multiple recipients.
• Some online multiplayer games use multicasting to synchronize game state among players.
• Multicast can be used in large-scale video conferencing where the same video feed is viewed by multiple participants.
• How does IGMP work?
• Hosts send IGMP messages to their local multicast router, indicating their interest in joining a specific multicast group.
• If a host no longer wishes to receive messages for a specific multicast group, it sends a leave group message.
• Multicast routers send query messages to determine which hosts belong to a multicast group.
• When a device wants to send or listen to multicast data for a specific multicast IP address, that IP address is mapped to a corresponding multicast MAC address. This mapping is deterministic, meaning the same multicast IP will always map to the same multicast MAC. For IPv4, the MAC address range 01:00:5E:00:00:00 to 01:00:5E:7F:FF:FF is reserved for multicast.
• When multicast data is transmitted on the local network, it uses the derived multicast MAC address. Devices on the network that have expressed interest in that multicast group (via IGMP) will listen for frames with that multicast MAC address and process them.
• For example: imagine a scenario in a corporate LAN where a video conference is being multicast to multiple participants.
1. The video conferencing server streams the video to a multicast IP address, say 239.1.2.3.
2. This multicast IP address maps to a specific multicast MAC address based on the aforementioned deterministic mapping.
3. Devices (computers of the participants) that want to join this video conference will use IGMP to express their interest in the multicast group 239.1.2.3.
4. The network switch, aware of the IGMP memberships, will efficiently forward the video stream (using the multicast MAC address) only to the ports where the interested devices are connected.
5. The devices receive the video stream frames, identify them by the multicast MAC address, and then process the data, displaying the video to the participants.

What is a "frame"?

• In the context of computer networking, data is transmitted across networks in chunks or packets. When we talk about the Data Link layer (Layer 2) of the OSI model, which is where MAC addresses operate, these packets are often referred to as "frames." A frame is essentially a package of information that includes not just the data being sent, but also source and destination MAC addresses, error-checking information, and other control data.
• Any device on the network can send a broadcast frame, depending on its needs:
• A new device that just connected to the network might send a broadcast to discover services like DHCP.
• If a computer wants to communicate with another device on its local network but doesn't know its MAC address, it might send a broadcast ARP request to find out.
• Some network diagnostic tools might send broadcasts to discover devices or services on the local network.

How does load balancing work at a DNS level?

• The most basic form of DNS load balancing is using Round Robin DNS. If you specify multiple A (or AAAA for IPv6) records for a domain, the DNS server will typically rotate through them when responding to requests. This can distribute connections among several servers. However, it's a very rudimentary form of load balancing because it doesn't take into account the health or the load of the servers. If one of the servers goes down, DNS would still distribute traffic to it unless you manually remove that record or have some other automated health check process in place.
• Some DNS providers offer geolocation-based DNS services. Based on the requester's geographic location, the DNS server will return the IP address of the server closest to them. This helps reduce latency and can also be used to direct traffic to region-specific servers or data centers.
• Services like AWS Route 53 allow you to set weights for your DNS records. This means you can have 70% of your traffic go to one server and 30% to another, for instance.
• Some advanced DNS services can automatically remove an A record from the rotation if the server it points to fails a health check. This provides a basic level of failover in case one of your servers becomes unreachable.
• Some third-party services specialize in DNS-based load balancing and offer more advanced features, such as real-time traffic analysis, intelligent routing based on server load or performance, etc.
• For most DNS providers, setting up these features involves logging into their web interface and configuring your domain's DNS settings. Some might offer APIs to automate or programmatically control these configurations.
• Exaples of DNS services that offer DNS level load balancing and DNS failover:
• Amazon's Route 53 DNS service provides a variety of advanced traffic routing policies, including simple, weighted, latency-based, failover, and geolocation routing.
• Known primarily for its content delivery network (CDN) and security services, Cloudflare also offers DNS load balancing and health checks. They provide geo-routing, failover, and even session affinity.
• Before its acquisition by Oracle, Dyn was one of the premier independent DNS providers. Oracle's version of the service offers advanced traffic management, including internet performance optimization, load balancing, and failover solutions.
• Part of Google Cloud Platform, their DNS solution supports various types of load balancing and traffic routing, including global load balancing across worldwide locations.
• While it's more than just a DNS service, Microsoft Azure's Traffic Manager uses DNS to direct client requests to the most appropriate service endpoint based on a variety of traffic-routing methods and the health of the endpoints.
• DNS Made Easy offers a feature called Global Traffic Director, which allows for regional-based DNS queries. They also provide DNS failover to redirect traffic in case your primary server fails.
• Akamai, a leading CDN provider, offers a DNS product that provides both speed and resilience. It offers fast DNS resolutions while also defending against DDoS attacks. It also supports geo-based routing and failover.
• NS1 offers a platform for DNS and application traffic management. They provide intelligent traffic routing, real-time server health checks, and geo-routing capabilities.

What is the difference between a proxy and a VPN?

• Both VPNs (Virtual Private Networks) and proxies are used to reroute internet traffic, masking the user's actual IP address.
• A VPN establishes a secure, encrypted connection between your device and a remote server, operated by the VPN service provider. All your internet traffic is routed through this connection. This encryption adds a layer of privacy and security, making it difficult for third parties to intercept or eavesdrop on your online activities. VPNs operate at the system level, redirecting all of the device's internet traffic, including every application that accesses the internet. Generally, a VPN might have a more significant impact on connection speed due to encryption and the distance to the VPN server.
• A proxy server acts as an intermediary between your device and the internet. It forwards requests and responses on your behalf, hiding your real IP address. Unlike VPNs, proxies usually don't encrypt your data, meaning the information might be exposed to third parties. Proxies often work at the application level, meaning they are configured per application (such as a web browser), not for the entire device.