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Networking
| Question | Answer |
|---|---|
| What technology helps users get connected and stay secure? VPN | Virtual Private Network (VPN) A VPN is used by clients to connect securely to a private network. |
| The Domain Name System (DNS) network service uses which Transport Layer Protocol? | User Datagram Protocol (UDP) DNS uses the UDP protocol for queries and resolution. It’s a connectionless protocol. |
| A concept that involves iterating over a list of items one by one in an orderly fashion is known as: Round Robin. | Round Robin ensures a fairly equal distribution across its members. |
| There are 13 Root Name Servers. | |
| What service acts on behalf of a Client in order to access another service? Proxy Server | Proxy Server - Proxies sit between Clients and other servers to facilitate connections. |
| A complete Fully Qualified Domain Name (FQDN) is limited to how many characters? 255 | 255 |
| What benefits does the Domain Name System (DNS) provide? | Ease of address memorization, and easy mapping to a new IP address. |
| Many of the Protocols and devices we use have built in functionalities to help protect against networking problems. These functionalities are known as Error Detection and Error Recovery. | |
| Error-Detection | The ability for a protocol or program to determine that something went wrong. |
| Error-Recovery | The ability for a protocol or program to attempt to fix it. |
| Cyclical Redundancy Checks are used by multiple layers to make sure the correct data is received by the receiving end. If a CRC value doesn’t match the data payload, the data is discarded. | At this point, the Transport Layer will decide if the data needs to be reset. But even with all these safeguards in place, errors still pop up: Misconfigurations occur, Harware break down, and system incompatibilities come to light. |
| Internet Control Message Protocol (ICMP) | ICMP is mainly used by a Router or Remote Host to communicate why a transmission has failed back to the origin of the transmission. |
| When a network error occurs the device that detects it needs some way to communicate this to the source of the problematic traffic. | The Router doesn’t know to route to a destination, or a certain port isn’t reachable. The TTL of an IP datagram expired and no further Router hops will be attempted. For all these situations, (ICMP) is used to communicate these issues. |
| The payload for an Internet Control Message Protocol (ICMP) packet exists entirely so the recipient of the message knows which of their transmissions caused the error being reported. | ICMP wasn’t developed for Humans to interact with. The point is these sorts of error messages can be delivered between networked Computers automatically. But, a specific tool very useful to Human operators is called Ping. |
| Ping - Allows us to send a special type of Internet Control Message Protocol (ICMP) message called an Echo Request. An ICMP Echo Request essentially just asks a destination, Hey are you there? | If the destination is up and running, along with being able to communicate on the network. It will send back a ICMP Echo Reply message type. |
| On the Windows OS, the Ping defaults to sending 4 Echo requests. In all environments PING supports a number of command lines allowing us to change its behavior: Number of Echo Requests to send, how large they should be, how quickly they’re sent. | On Linux and Mac OS, the Ping Comand will run until it’s interrupted by an end user sending an interrupt event. This done by pressing the Control key and the C key at the same time. |
| Traceroute - A utility that lets us discover the path between two nodes, and gives us information about each hop along the way. | |
| Subnet Mask - A way for a Computer to use and Operators to determine if an IP address exists on the same network. | |
| Through a manipulation technique of the TTL field at the IP level. When the TTL field reaches zero, the packet is discarded and an ICMP Time is exceeded message is sent back to the originating host. | |
| Traceroute uses the TTL field by first setting it to one for first packet, then two for the second, three for the third and so on. By doing this action, Traceroute make the very first packet sent will be discarded by the first Router hop. | This results in the ICMP Time Exceed Message, the second packet will make it to the second router, the third will make it to the third, and so on. This continues until the packet finally makes it all the way to it’s destination. |
| The Linux and Mac OS program Traceroute is known by a slightly different name on Windows. It’s referred to as: tracert | These programs operate slightly different and have slightly different names. |
| An organization responsible for assigning individual domain names to other organizations or individuals is known as a DNS Registrar. | We can use a Registra to register a Domain Name. |
| PaaS stands for: Platform as a Service. | PaaS enables us to run applications without requiring an entire server to do so. |
| Traceroute uses UDP packets on Linux and Mac OS operating systems. | On Linux and Mac OS, Traceroute sends UDP packets to very high port numbers. |
| The IP address 127.0.0.1 is an IPv4 loop back address, and IP address ::1 is known as a IPv6 loopback address. | A loopback address points to itself and is used for troubleshooting purposes. |
| An IPv6 address is 128 bits in size. | IPv6 addresses are 128 bits compared to 32 bits of an IPv4 IP address. |
| On a Windows system, the Ping command sends 4 Echo Requests. | Linux and Mac OS systems send Echo Requests until the Ping command is stopped. A Windows system sends only 4 Echo Requests by default. |
| With the nslookup command in interactive mode, it’s accessed by providing the command with no options. | When using the nslookup command with no options, the command provides a prompt to enter additional information in what is called an Interactive Mode. |
| Which IPv6 field is identical in purpose to the TTL field in an IPv4 header? Hop limit. | The Hop limit field is an 8-bit field that’s identical in purpose to the Time To Live (TTL) field in an IPv4 header. |
| For IPv6 traffic to travel on an IPv4 network, which two technologies are used? | An IPv6 tunnel is used to encapsulate data between IPv6 tunnel servers. |
| What size is an IPv6 payload field? 16-bit | The Payload length field is a 16-but field that defines how long the data payload section of the datagram is. |
| On Windows, one of the tools we can use to verify connectivity to a specific port is: Test-NetConnection. | Test-NetConnection allows us to test many things, including connectivity to a specific port on a remote host. |
| The protocol used to communicate network errors is known as Internet Command Message Protocol (ICMP). | Internet Conmsnd Message Protocol (ICMP) is used to communicate errors back to the client. |
| Sometimes we need to know if network connectivity is working at the Transport Layer. For this, there are 2 powerful tools at our disposal: Netcat (nc) on Linux and MacOS, and Test-NetConnecrion on Windows. | The Netcat tool can be run on through the command nc, and has 2 mandatory arguments, a host and a port. Running this command would try to establish a connection on port 80 to Google.com: nc google.com 80 |
| If connection fails, the command will exit, if it succeeds, we’ll see a blinking cursor, waiting for more input. This is the way for us to send Application Layer data to the listening service from our keyboard. | If we’re curious about the status of a report, we can issue the command with a -x flag: which stands for zero input/output mode. A -v flag stands for verbose. The command looks like this: nc -v -z google.com 80 |
| By issuing the Netcat command with the -Z and -V flags, the command’s output will simply tell us if a connection to the port in question possible or not, like this: Connection to google.com 80 port [tcp/ succeeded! | |
| On Windows, when running a Test-NetConnection with only a host specified will default to using an ICMP echo request like the program ping. But, it will display much more data, including the Data Link Layer protocol being used. | When we issue Test-NetConnection with the -Port flag, we can ask it to test connectivity to a specific port. Ex: Command tests a TCP connection to google.com: Test-NetConnection -ComputerName google.com -Port 80 |
| One of the Level 3 public Domain Name System (DNS) servers is: 4.2.2.3 | Level 3’s public DNS servers are 4.2.2.1 through 4.2.2.6 |
| A DNS resolver tool available on all major desktop operating systems is: nslookup | nslookup is available by default on Windows, Mac OS, and Linux. |
| The organization responsible for DNS at a global level is ICANN | ICANN is responsible for DNS at a global level. |
| Almost every Host File in existence will, in the very least, contain a line that reads 127.0.0.1 localhost, most likely followed by ::1 localhost, where ::1 is the loopback address for IPv6. | Since DNS is everywhere, Host Files are used much anymore. But they still exist and are still important to know about. Host files are popular way for Computer Viruses to disrupt and redirect users’ traffic. |
| Some software require specific entries in the Host Files to operate properly. It’s not a great idea to use Host Files today, but they do have some useful troubleshooting purposes that can help in IT support. | Host Files are examined before a DNS resolution attempt occurs on just about every major Operating System. This lets us force an individual Computer to think a certain Domain Name always points at a specific IP. |
| Cloud Computing - A technological approach where computing resources are provisioned in a shareable way, so that lots of users get what they need, when they need it. | At the heart of cloud computing is a technology known as Hardware virtualization. Hardware virtualization is a core concept of how Cloud Computing technologies work. |
| Hardware Virtualization allows the concept of a physical Machine and logical Machine to be abstracted away from each other. With Virtualization, a single physical Machine called a Host could run many individual virtual instances called guests. | An Operating System expects to be able to communicate with the underlying hardware in certain ways. Hardware Virtualization platforms employ a Hypervisor. |
| A Hypervisor is a piece of Software that runs and manages Virtual Machines while also offering these Guests a virtual operating platform that’s indistinguishable from actual Hardware. | A Hypervisor manages many virtual instances running on a single host. |
| A Hybrid Cloud is a combination of Public Cloud and a Private Cloud. | A Hybrid Cloud runs some services on a Cloud provider and some services in-house. |
| Any Address that begins with FF00:: is used for Multicast. Any Address that begins with FE80:: are used for link-local unicast. | Multicast - A way of addressing groups of Hosts all at once. Link-local unicast addresses - Allow for local network segment communications and are configured based upon a Host’s MAC address. |
| Algorithm - A series of steps that solve specific problems. | The very first example of Computer programming. |
| Cryptography - The art of writing and solving codes. | |
| Open Source - Anyone could modify and share it. | For example: Linux - The largest Open Source Operating System! |
| Binary System - The communication that a Computer uses, also known as a Base-2 numeral system. (1s and 0s) We group binary into 8 numbers or bits. Technically, a bit is a binary digit. A group of 8 Bits is referred to as a Byte. | Each Byte can store one character, and we can have 256 possible values thanks to the Base-2 system. Computers only talk in 1s and 0s. |
| We count 0 as a number so the highest value we can have is 255. | 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255 |
| Abstraction - To take a relatively complex system and simply it for our use. | An Error message is an example of an Abstraction. |
| ICMP packet - 1st field is the TYPE field, 8 Bits along which specifies what type of message is being delivered. | Some examples are Destination unreachable, or time exceeded. |
| Rest of Header = 32 bit field | This field is optionally used by some of the specific types and codes to send more data. |
| Computer Networking - The name we’ve given to the full scope of how Computers communicate with each other. | Protocol - A defined set of standards that Computers must follow in order to communicate properly. |
Created by:
kwedde172