Comp Networks- Pre-study | WAN vs LAN, bridging and routing, IP networks

Question 1

A ______ ____ _____ (____) is defined as a telecommunications network that helps to connect devices (end-user devices and servers) that are situated several kilometers or even hundreds of kilometers away from each other.

Answer 1

wide area network (WAN)

Question 2

A WAN may be public – for example, _______is a type of WAN as it enables connectivity and data exchange between devices situated on opposite ends of the world.

Answer 2

the internet

Question 3

a _____ WAN in an enterprise, useful for securely sharing data and resources between geographically distributed headquarters, branch offices, retail stores, logistical hubs, and other similar locations. The key factor characterizing WAN is that it spans a geographically wide area.

Answer 3

private

Question 4

A _____ _____ ____ (______) is defined as a telecommunications network that helps connect devices (end-user devices and servers) that are situated close to each other, typically inside a radius of one kilometer.

Answer 4

local area network (LAN)

Question 5

LAN is widely used in both consumer and enterprise use cases. For example, you may have a collection of connected devices like a smart refrigerator, a laptop, a voice recognition-enabled TV, and a smart home console inside a person’s house. This setup uses LAN technology to enable _____ exchange between these devices so that the homeowner can access and control their functionalities seamlessly.

Answer 5

data

Question 6

a medium-sized office campus may have hundreds of laptops and workstations, several meeting room systems, connected printers, and attendance kiosks, servers, and other devices, also set up using LAN. as long as the devices are within a compatible geographic range, you can connect them via ____ _____. This need for proximity is the key factor characterizing LAN.

Answer 6

LAN technology

Question 7

LAN is a component of a larger WAN environment

This is a critical differentiating factor between WAN and LAN. Multiple local area networks together form a _____ _____ _____. For example, each individual consumer may have a separate local area network at their home. Multiple personal LANs may be connected via a wide area network managed by the region’s government. Thousands of LANs around the globe form the public internet, which is also a wide area network. In an enterprise context, each office location may be connected via LAN, and all LANs may communicate with the company’s headquarters and with each other through a secure private WAN.

Answer 7

wide area network

Question 8

WAN and LAN involve two or more nodes that are being connected

As a prerequisite for both WAN and LAN, you need two or more computing nodes that are being connected.

Answer 8

This could be two end-user devices, an end-user device and a server, smart office or home appliances, or any other networked endpoint. You cannot have either a WAN or LAN environment without at least two separate nodes in place, which are at some distance from each other.

Question 9

WAN and LAN use TCP/IP protocols

While LAN and WAN have different underlying technologies, both rely on the transmission control protocol/internet protocol (TCP/IP) model. TCP/IP is a collection of internet connectivity standards and protocols first developed by the department of defense in the 1960s.

Answer 9

It segments a network environment into four discrete layers: the application, transport, internet, and network access layers. Both WAN and LAN rely on TCP/IP.

Question 10

Both LAN and WAN may be wireless or wired in nature

You may leverage both LAN and WAN to connect devices using wires or through wireless transmission. Fiber-optic, coaxial, and twisted-pair cabling are the three main types of wires used for LAN and WAN connectivity.

Answer 10

Wireless WAN and LAN environments both rely on 3G, 4G, 5G, and Wi-Fi signals to enable network connectivity.

Question 11

Both LAN and WAN can be used by consumers and enterprises alike

Consumers typically use publicly owned WAN infrastructure, although visitors in an enterprise or official establishment may also use private WAN connectivity. Consumers may also have privately owned local area networks in their homes and may lease LAN services from local providers.

Answer 11

Enterprises may design local area networks for individual offices and operational locations or for mid-sized to large campuses. They may also have privately owned WAN spanning multiple cities or even connecting different countries for secure data transmissions.

Question 12

WAN providers

Answer 12

Silver Peak, a provider of WAN appliances, WAN optimization, and SD-WAN solutions

Aryaka, a cloud-first managed SD-WAN service provider

Meraki, Cisco’s portfolio of WAN hardware and software solutions

Masergy, a leading cloud and MPLS-based WAN provider

Question 13

LAN providers

Answer 13

Mist, a provider of AI-powered wireless and wired LAN

Cisco, a leading LAN hardware and security company

Aruba, an HPE subsidiary specializing in wireless LAN solutions

Extreme Networks, a cloud-based LAN management provider

Question 14

IP was designed to support global packet switching network infrastructure. Ethernet bridging was designed to emulate a single shared cable. Various design decisions made in IP or Ethernet bridging were always skewed by these perspectives: scalability versus transparency.

Answer 14

design scope

Question 15

IP routers forward IP datagrams according to their IP routing tables and never make multiple copies of the same datagram. They drop datagrams sent to unknown destinations and tell the sending hosts they did so. Bridges have to emulate a shared cable and thus forward frames sent to unknown destinations to all active ports but the one on which the frame was received (flooding). In short, routing is “forwarding based on presumption of knowledge”, bridging is “forwarding by guessing”.

Answer 15

Forwarding

Question 16

IP (and most other layer-3 protocols) has a hop count in its header. Ethernet header does not have a hop count (neither do most other layer-2 protocols). Using hop count, loops can be detected even when they cannot be prevented (uRPF does a decent job of loop prevention in non-asymmetric networks, but that’s a different story).

Even worse, the forwarding by guessing bridging paradigm can create multiple copies of a looped packet sent to unknown destination. The number of copies grows exponentially with each iteration of the loop, quickly resulting in a total network meltdown.

Answer 16

Loop detection

Question 17

Routers stop multicast or broadcast packets unless they are configured to forward them. Decent multicast implementations allow hosts to register to multicast streams and the routers deliver multicast packets only to those hosts or segments that actually need them.

Transparent bridges have to emulate a shared cable where every station can receive a broadcast or multicast frame. They are thus bound to flood multicast/broadcast frames.

Some layer-2 bridges support IGMP snooping and other mechanisms that should limit the amount of IP multicast propagated in unwanted directions. These measures work only for known (IP) multicast addresses; bridges still have to flood frames sent to unknown multicast destinations.

Most bridges can rate-limit the flooding process, reducing the chances of a single runaway host bringing the whole network to a standstill. Nonetheless, a determined intruder can use the rate-limiting mechanisms for an effective DoS attack where the bogus multicast traffic interferes with crucial protocols like ARP.

Answer 17

Multicast

Question 18

IP routing tables are built by routers exchanging (somewhat) authoritative information: their connected subnets and their static routes. Bridging tables are built by guessing – by listening to the traffic and extracting source MAC addresses from the frames. The guessed information is never exchanged between the bridges (ESADI in TRILL is an exception, but even ESADI information is not authoritative).

Answer 18

Forwarding tables

Question 19

Layer-3 addresses are configurable and usually include some topology information, allowing the layer-3 routing to scale. Layer-2 addresses are supposed to be static (hardwired) and are (within a single network) randomly scattered around the network.

Answer 19

Addressing

Question 20

All layer-3 protocols have some mechanism that aggregates forwarding information, allowing them to scale. The “desktop protocols” (Cisco’s invention, not mine), including AppleTalk, IPX and Banyan Vines performed routing based on networks (cable ranges in Appletalk), which were very similar to fixed-prefix IP subnets. DECnet, CLNS and SNA have areas and perform host-based routing within an area, but still use only area addresses in “long-distance” (inter-area) routing to scale. Classless routing with IP prefixes allows you to build a multi-layer hierarchy.

Transparent bridging forwards frames to randomly scattered layer-2 addresses and thus cannot have a scaling mechanism.

Novel approaches to bridging (TRILL and 802.1ad) introduce a bridging hierarchy (or a bridging/routing hierarchy in case of TRILL), in which inner bridges (provider bridges in 802.1ad) know just the MAC address of edge bridges. VLANs deployed on edge bridges further limit the amount of information a single edge bridge must carry. Still, a single bridged domain cannot scale.

Answer 20

scalability

Question 21

The “forwarding by learning” paradigm makes it extremely easy to spoof a bridged network: send frames with wrong source MAC address. Spoofing a routed network is somewhat harder; you have to hack the routing protocol.

Bridges reduce the risk of spoofing by implementing port security, dynamic ARP inspection and DHCP snooping; workaround measures trying to solve a problem that shouldn’t have existed in the first place. You cannot secure an environment designed to emulate a single shared cable (at least not without breaking some eggs).

Answer 21

spoofing

Question 22

IP was designed to span a multitude of physical media with different characteristics and supports datagram fragmentation and path MTU discovery. Bridging was designed to connect segments with uniform technology, which was fine as long as the maximum Ethernet MTU was constant. Introduction of jumbo frames has created a “somewhat more complex” environment, where bridging between Ethernet segments can fail spectacularly.

Answer 22

fragmentation

Question 23

Out-of-order packets are a fact of life in any multipath topology (including any layer-3 network). Layer-3 protocols were thus designed to deal with them, either rearranging them (TCP) or dropping them (most UDP applications).

Protocols that pretend the hosts communicate on a shared cable tend to ignore the out-of-order problems; some protocols might even terminate the session when receiving one. SNA was one of those protocols, forcing Cisco to implement FST, which dropped any out-of-order packets. The requirement to deliver packets in order significantly complicates any advanced bridging implementation (for example, TRILL).

Answer 23

Out-of-order packets

Question 24

IP can (by definition) be used on all data link layer technologies. You can mix-and-match various technologies as needed: Ethernet for access LAN, Gigabit Ethernet with large MTU for data center, HDLC, PPP, Frame Relay or ATM for WAN links. Datagram transport across all the media is always (close to) optimal.

Bridging forces you to use a single layer-2 technology (for example, Ethernet) everywhere and emulate the chosen layer-2 technology across all other media. This requirement leads to baroque architecture used in DSL networks and emulation jumbles like LANE or VPLS.

Answer 24

Mixed media

Question 25

Every location or device on a network must be addressable. This means that it can be reached by referencing its designation under a predefined system of addresses. In the normal TCP/IP model of network layering, this is handled on a few different layers, but usually when we refer to an address on a network we are talking about an ____ _______.

Answer 25

IP address

Question 26

IP addresses allow network resources to be reached through a _____ ______. If one computer wants to communicate with another computer, it can address the information to the remote computer’s IP address. Assuming that the two computers are on the same network, or that the different computers and devices in between can translate requests across networks, the computers should be able to reach each other and send information.

Answer 26

network interface

Question 27

Each IP address must be unique on its own network. Networks can be isolated from one another, and they can be bridged and translated to provide access between distinct networks. A system called _____ ______ ______, allows the addresses to be rewritten when packets traverse network borders to allow them to continue on to their correct destination. This allows the same IP address to be used on multiple, isolated networks while still allowing these to communicate with each other if configured correctly.

Answer 27

Network Address Translation

Question 28

There are two revisions of the IP protocol that are widely implemented on systems today: IPv4 and IPv6. IPv6 is slowly replacing IPv4 due to improvements in the protocol and the limitations of IPv4 address space. Simply put, the world now has too many _____-______ devices for the amount of addresses available through IPv4.

Answer 28

internet-connected

Question 29

IPv4 addresses are ___-bit addresses. Each byte, or 8-bit segment of the address, is divided by a period and typically expressed as a number 0–255. Even though these numbers are typically expressed in decimal to aid in human comprehension, each segment is usually referred to as an octet to express the fact that it is a representation of 8 bits.

A typical IPv4 address looks something like this:

192.168.0.5

Answer 29

32

Question 30

A typical IPv4 address looks something like this:

192.168.0.5

The lowest value in each octet is a ____, and the highest value is _____.

We can also express this in binary to get a better idea of how the four octets will look. We will separate each 4 bits by a space for readability and replace the dots with dashes:

1100 0000 - 1010 1000 - 0000 0000 - 0000 0101

Recognizing that these two formats represent the same number

Answer 30

0
255

Question 31

IP addresses are typically made of two separate components. The first part of the address is used to identify the ______ that the address is a part of. The part that comes afterwards is used to specify a specific ____ within that network.

Where the network specification ends and the host specification begins depends on how the network is configured.

Answer 31

network
host

Question 32

IPv4 addresses were traditionally divided into five different “classes”, named A through E, meant to differentiate segments of the available addressable IPv4 space. These are defined by the first four bits of each address. You can identify what class an IP address belongs to by looking at these bits.

Answer 32

Class A

0— : If the first bit of an IPv4 address is “0”, this means that the address is part of class A. This means that any address from 0.0.0.0 to 127.255.255.255 is in class A.

Class B

10– : Class B includes any address from 128.0.0.0 to 191.255.255.255. This represents the addresses that have a “1” for their first bit, but don’t have a “1” for their second bit.

Class C

110- : Class C is defined as the addresses ranging from 192.0.0.0 to 223.255.255.255. This represents all of the addresses with a “1” for their first two bits, but without a “1” for their third bit.

Class D

1110 : This class includes addresses that have “111” as their first three bits, but a “0” for the next bit. This address range includes addresses from 224.0.0.0 to 239.255.255.255.
Class D addresses are reserved for multi-casting protocols, which allow a packet to be sent to a group of hosts in one movement.

Class E

1111 : This class defines addresses between 240.0.0.0 and 255.255.255.255. Any address that begins with four “1” bits is included in this class.
Class E addresses are reserved for future and experimental use, and are largely not used.

Question 33

IPv4 Address classes:

Traditionally, each of the regular classes (A–C) divided the networking and host portions of the address differently to accommodate different sized networks. Class A addresses used the remainder of the first octet to represent the network and the rest of the address to define hosts. This was good for defining a few networks with a lot of hosts each.

The class B addresses used the first two octets (the remainder of the first, and the entire second) to define the network and the rest to define the hosts on each network. The class C addresses used the first three octets to define the network and the last octet to define hosts within that network.

Answer 33

The division of large portions of IP space into classes is now almost a legacy concept. Originally, this was implemented as a stop-gap for the problem of rapidly depleting IPv4 addresses (you can have multiple computers with the same host if they are in separate networks). This was replaced largely by later schemes that we will discuss below.

Question 34

Reserved private ranges

Answer 34

There are also some portions of the IPv4 space that are reserved for specific uses.

One of the most useful reserved ranges is the loopback range specified by addresses from 127.0.0.0 to 127.255.255.255. This range is used by each host to test networking to itself. Typically, this is expressed by the first address in this range: 127.0.0.1.

Each of the normal classes also have a range within them that is used to designate private network addresses. For instance, for class A addresses, the addresses from 10.0.0.0 to 10.255.255.255 are reserved for private network assignment. For class B, this range is 172.16.0.0 to 172.31.255.255. For class C, the range of 192.168.0.0 to 192.168.255.255 is reserved for private usage.

Any computer that is not hooked up to the internet directly (any computer that goes through a router or other NAT system) can use these addresses at will.

There are additional address ranges reserved for specific use-cases

Question 35

The process of dividing a network into smaller network sections is called _______. This can be useful for many different purposes and helps isolate groups of hosts from each other to deal with them more easily.

Answer 35

subnetting

Question 36

The amount of the address that each of these take up is dependent on the class that the address belongs to. For instance, for class C addresses, the first 3 octets are used to describe the network. For the address 192.168.0.15, the 192.168.0 portion describes the network and the 15 describes the host.

By default, each network has only one subnet, which contains all of the host addresses defined within. A netmask is basically a specification of the amount of address bits that are used for the network portion. A subnet mask is another netmask within used to further divide the network.

Answer 36

Each bit of the address that is considered significant for describing the network should be represented as a “1” in the netmask.

Question 37

system called Classless Inter-Domain Routing, or CIDR, was developed as an alternative to traditional subnetting. The idea is that you can add a specification in the IP address itself as to the number of significant bits that make up the routing or networking portion.

For example, we could express the idea that the IP address 192.168.0.15 is associated with the netmask 255.255.255.0 by using the CIDR notation of 192.168.0.15/24. This means that the first 24 bits of the IP address given are considered significant for the network routing.

Answer 37

This allows us some interesting possibilities. We can use these to reference “supernets”. In this case, we mean a more inclusive address range that is not possible with a traditional subnet mask. For instance, in a class C network, like above, we could not combine the addresses from the networks 192.168.0.0 and 192.168.1.0 because the netmask for class C addresses is 255.255.255.0.

However, using CIDR notation, we can combine these blocks by referencing this chunk as 192.168.0.0/23. This specifies that there are 23 bits used for the network portion that we are referring to.

Question 38

_______: In networking, a connection refers to pieces of related information that are transferred through a network. Generally speaking, a connection is established before data transfer (by following the procedures laid out in a protocol) and may be deconstructed at the end of the data transfer.

Answer 38

Connection

Question 39

_________: A packet is the smallest unit that is intentionally transferred over a network. When communicating over a network, packets are the envelopes that carry your data (in pieces) from one end point to the other.

Answer 39

Packet

Question 40

______ _____: A network interface can refer to any kind of software interface to networking hardware. For instance, if you have two network cards in your computer, you can control and configure each network interface associated with them individually.

Answer 40

Network interface

Question 41

______: stands for “local area network”. It refers to a network or a portion of a network that is not publicly acces

Answer 41

LAN

Question 42

______: stands for “wide area network”. It means a network that is much more extensive than a LAN. While WAN is the relevant term to use to describe large, dispersed networks in general, it is usually meant to mean the internet, as a whole.

Answer 42

WAN

Question 43

If an interface is said to be connected to the WAN, it is generally assumed that it is reachable through the internet.

_______: A protocol is a set of rules and standards that define a language that devices can use to communicate. There are a great number of protocols in use extensively in networking, and they are often implemented in different layers.

Answer 43

Protocol

Question 44

Some low level protocols are TCP, UDP, IP, and ICMP. Some familiar examples of application layer protocols, built on these lower protocols, are HTTP (for accessing web content), SSH, and TLS/SSL.

_____: A port is an address on a single machine that can be tied to a specific piece of software. It is not a physical interface or location, but it allows your server to be able to communicate using more than one application.

_____: A firewall is a program that decides whether traffic coming or going from a server should be allowed. A firewall usually works by creating rules for which type of traffic is acceptable on which ports. Generally, firewalls block ports that are not used by a specific application on a server.

______: NAT stands for network address translation. It is a way to repackage and send incoming requests to a routing server to the relevant devices or servers on a LAN. This is usually implemented in physical LANs as a way to route requests through one IP address to the necessary backend servers.

_____: VPN stands for virtual private network. It is a means of connecting separate LANs through the internet, while maintaining privacy. This is used to connect remote systems as if they were on a local network, often for security reasons.

Answer 44

Port
Firewall
NAT
VPN

Question 45

The TCP/IP model, more commonly known as the Internet protocol suite, is a widely adopted layering model. It defines the four separate layers:

_______: In this model, the application layer is responsible for creating and transmitting user data between applications. The applications can be on remote systems, and should appear to operate as if locally to the end user. This communication is said to take place between peers.

______: The transport layer is responsible for communication between processes. This level of networking utilizes ports to address different services.

_____: The internet layer is used to transport data from node to node in a network. This layer is aware of the endpoints of the connections, but is not concerned with the actual connection needed to get from one place to another. IP addresses are defined in this layer as a way of reaching remote systems in an addressable manner.

____: The link layer implements the actual topology of the local network that allows the internet layer to present an addressable interface. It establishes connections between neighboring nodes to send data.

As you can see, the TCP/IP model is abstract and fluid. This made it popular to implement and allowed it to become the dominant way that networking layers are categorized.

Answer 45

Application
Transport
Internet
Link

Question 46

Interfaces are networking communication points for your computer. Each interface is associated with a physical or virtual networking device.

your server will have one configurable _____ _____ for each Ethernet or wireless internet card you have.

In addition, it will define a virtual network interface called the “loopback” or ______ ______. This is used as an interface to connect applications and processes on a single computer to other applications and processes. You can see this referenced as the “lo” interface in many tools.

Many times, administrators configure one interface to service traffic to the internet and another interface for a LAN or private network.

In datacenters with private networking enabled (including DigitalOcean Droplets), your ____ will have two networking interfaces. The “eth0” interface will be configured to handle traffic from the internet, while the “eth1” interface will operate to communicate with a private network.

Answer 46

network interface
localhost interface
VPS

Question 47

Protocols - medium access control:

Medium access control is a communications protocol that is used to distinguish specific devices. Each device is supposed to get a unique, hardcoded ____ _____ _____ (____ ______) when it is manufactured that differentiates it from every other device on the internet.

Addressing hardware by the MAC address allows you to reference a device by a unique value even when the software on top may change the name for that specific device during operation.

MAC addressing is one of the only protocols from the low-level ____ layer that you are likely to interact with on a regular basis.

Answer 47

media access control address (MAC address)
link

Question 48

Protocols - IP

The IP protocol is one of the fundamental protocols that allow the internet to work. IP addresses are unique on each network and they allow machines to address each other across a network. It is implemented on the internet layer in the ______ model.

Networks can be linked together, but traffic must be routed when crossing network boundaries. This protocol assumes an unreliable network and multiple paths to the same destination that it can dynamically change between.

Answer 48

TCP/IP

Question 49

______ stands for internet control message protocol. It is used to send messages between devices to indicate their availability or error conditions. These packets are used in a variety of network diagnostic tools, such as ping and traceroute.

Usually ICMP packets are transmitted when a different kind of packet encounters a problem. They are used as a feedback mechanism for network communications.

Answer 49

ICMP

Question 50

TCP stands for transmission control protocol. It is implemented in the transport layer of the TCP/IP model and is used to establish reliable connections.

TCP is one of the protocols that encapsulates data into packets. It then transfers these to the remote end of the connection using the methods available on the lower layers. On the other end, it can check for errors, request certain pieces to be resent, and reassemble the information into one logical piece to send to the application layer.

Answer 50

The protocol builds up a connection prior to data transfer using a system called a three-way handshake. This is a way for the two ends of the communication to acknowledge the request and agree upon a method of ensuring data reliability.

After the data has been sent, the connection is torn down using a similar four-way handshake.

TCP is the protocol of choice for many of the most popular uses for the internet, including WWW, SSH, and email.

Question 51

UDP stands for user datagram protocol. It is a popular companion protocol to TCP and is also implemented in the transport layer.

The fundamental difference between UDP and TCP is that UDP offers unreliable data transfer. It does not verify that data has been received on the other end of the connection. This might sound like a bad thing, and for many purposes, it is. However, it is also extremely important for some functions.

Answer 51

Because it is not required to wait for confirmation that the data was received and forced to resend data, UDP is much faster than TCP. It does not establish a connection with the remote host, it just sends data without confirmation.

Because it is a straightforward transaction, it is useful for communications like querying for network resources. It also doesn’t maintain a state, which makes it great for transmitting data from one machine to many real-time clients. This makes it ideal for VOIP, games, and other applications that cannot afford delays.

Question 52

______ stands for hypertext transfer protocol. It is a protocol defined in the application layer that forms the basis for communication on the web.

HTTP defines a number of verbs that tell the remote system what you are requesting. For instance, GET, POST, and DELETE all interact with the requested data in a different way.

Answer 52

HTTP

Question 53

_______ stands for domain name system. It is an application layer protocol used to provide a human-friendly naming mechanism for internet resources. It is what ties a domain name to an IP address and allows you to access sites by name in your browser.

Answer 53

DNS

Question 54

____ stands for secure shell. It is an encrypted protocol implemented in the application layer that can be used to communicate with a remote server in a secure way. Many additional technologies are built around this protocol because of its end-to-end encryption and ubiquity.

Answer 54

SSH