What happens when a node on one network establishes a tcp connection with a node on another network

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Kristen G.

AP CS

4 months, 1 week ago

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Some friends of yours work on wireless networks, and they're currently studying the properties of a network of mobile devices. As the devices move around (actually, as their human owners move around), they define a graph at any point in time as follows: there is a node representing each of the devices, and there is an edge between device and device if the physical locations of and are no more than 500 meters apart. (If so, we say that and are "in range" of each other. They'd like it to be the case that the network of devices is connected at all times, and so they've constrained the motion of the devices to satisfy the following property: at all times, each device is within 500 meters of at least of the other devices. (We'll assume is an even number.) What they'd like to know is: Does this property by itself guarantee that the network will remain connected? Here's a concrete way to formulate the question as a claim about graphs. Claim: Let G be a graph on n nodes, where n is an even number. If every node of has degree at least then is connected. Decide whether you think the claim is true or false, and give a proof of either the claim or its negation.

I'm taking the Coursera program, and i am in Course 2 w/ Networking. They don't actually give feedback or tell you if you're right or wrong on an "Explain X" question. So i am here, to see if it was actually correct by you guys' standards. Any criticisms are accepted.

What You’ll Do: In your own words, describe what happens at every step of our network model, when a node on one network establishes a TCP connection with a node on another network. You can assume that the two networks are both connected to the same router.

In the TCP/IP 5 Layer model, Session and Presentation are both bundled into the application layer, setting it aside from the OSI model which is used more in academic settings. Physical layer is considered the "Hands on" layer. Such as Networking devices, computers, servers, clients, with some of these terms being interchangeable.

Data link layer is responsible for the interchanging of data, such as using Ethernet. This layer will use the MAC address as way for direction, or addressing.

Network layer is considered the "Internet". This layer allows our model, or process to communicate networks through devices, like routers. We use IP in this addressing of this layer.

Transport layer uses TCP/UDP in segments, utilizing port #'s to ensure data is coming from the correct source, and going to the correct destination.

MAC address and IP Addresses are both "Identifiers." MAC addresses determine the physical machine, while IP addresses determine the network, or "general" location of a machine, such as this "MAC Address" computer is on this "IP Address.

TCP ports determine where information can be received. There are over 65000 ports available, with certain segments being reserved for certain tasks. Port 80 is the most common port used for receiving information, most specifically within a network. Firewalls are uses to block traffic from ports, for example, a network may only be receiving data into port 80, if a network is trying to send information to a different port, the firewall will block that traffic, as that port is closed.

Checksum checks are used to verify no data has been lost during the transport of information between networks or clients. Checksums will occur every time data moves from one point to another. During each checksum, if a TTL has changed, it will also reflect and check that.

Routing tables are used by routers to find the location of clients within a network, such as Network A is sending data to Network B. Computer 1 on Network A will send its data to its router on Network A, which will use its routing table to determine, Hey, this Computer 2 is in Network B, lets get it over there. Network B takes over full transport after it receives it.

TTL is Time To Live, which is determined by the router once it gathers information on how many "hops" it has to take to reach its destination. If it goes past the standard "64" then a time out is set to determine a faster way.

Overview: As an IT Support Specialist, it’s important that you fully grasp how networks work. You may need to troubleshoot different aspects of a network, so it’s important that you know how everything fits together. This assignment will help you demonstrate this knowledge by describing how networks function.

Your submission must include a detailed explanation of the following:

Physical layer
Data link layerAdvertisement
Network layer
Transport layer
MAC address
IP address
TCP port
Checksum check
Routing table
TTL

Five-Layer Network Model
Physical layer sends and receives signals on the physical wire or antenna to transmit the bits found in frames then the data link layer is used to determine if the frame received by the host contains the host’s MAC address. If it does, the data is forwarded up to the Network layer. When receiving data, network layer is used to determine if the packet received by the host contains the host’s IP address. If it does, the data is forwarded up to the Transport layer. The Transport layer establishes the connection between applications running on different hosts. It uses TCP for reliable connections and UDP for fast connections. It keeps track of the processes running in the applications above it by assigning port numbers to them and uses the Network layer to access the TCP/IP network, and the Application layer is where applications requiring network communications live.

----------------------------------------------------------- Questions---------------------------------------------------
In your own words, describe what happens at every step of our network model, when a node on one network establishes a TCP connection with a node on another network. You can assume that the two networks are both connected to the same router.

Your submission must include a detailed explanation of the following:

Physical layer
Data link layer
Network layer
Transport layer
MAC address
IP address
TCP port
Checksum check
Routing table
TTL

---------------------------------------------------------- Answer--------------------------------------------------------

How your data travels in the network and reaches its destination the complete explanation.

Lets first clear some networking terms:

• Physical layer. The physical device that interconnects the computers, their specification and how the signal is sent over this connection all comes in the physical layer. • Data link layer. It is basically all about defining a common way to interpret these signal so that a device can communicate with each other. The most common protocol used here is Ethernet. • Network layer. It allows different networks to communicate with each other using devices called routers • Transport layer. The transport layer finds which client and server programs are supposed to get that data. The most common protocol used here is TCP/IP. • MAC address. It is the address embedded in your hardware device (which will constitute a node of the network) permanently during its manufacturing. • IP address. Unlike the Mac address, it is not permanent and not embedded on any hardware it is the address of network it might change when you are at home connected with the wifi and different when you are connected with the railway station's wifi even the devices in both cases are same. • TCP port.

A port is a 16-bit number

that's used to direct traffic to specific services running on a networked computer. For example, port 80 is a port in which a web server listens for the web request. • Checksum check. It is a method used to check the correctness of data during the transmission from one place to another. • Routing table. It is a table in which the router device used to locate the destination IP address. • TTL or time to leave is the value assigned in the TTL field which tells the data when to leave the network. Let's begin our journey. Suppose there are two networks Network A and Network B with network space 9.5.4.0/24 and 125.5.45.0/24 respectively. These two networks are connected to the same router with two network interface having IP 9.5.4.1(on network A) and 125.5.45.1(on network B).

Now suppose a laptop or desktop which is a client in this case which is a part of the Network A having IP 9.5.4.23. Again assume that a server which is connected to Network B having IP address 125.5.45.34 and have a web server which is listening on port 80.

Now our clients want to access a website whose IP address is 125.5.45.34. He opens any browser and entered this IP address in the search bar and hits enter. The browser then communicates with the local networking stack, which is the part OS responsible for managing networking functions. Browser tells that it wants to establish a TCP connection with the server 125.5.45.34 through port 80. Then networking stack will check its own subnet and finds that 125.5.45.34 is on another network so the client has to send data through its gateway which have the network interface of

9.5.4.1. Then the client checks its ARP table to find out what is the MAC address of its gateway. There are two possibilities:

It finds the MAC address.
It doesn't find the MAC address.
If it didn't find first it will get it through an ARP request and then continue as described below :

Our client then makes an ARP request for IP 9.5.4.1 which is sent to all devices connected to the same network having the same hardware broadcast ID of all Fs. When the router on this network receives this request it knows that it is for me and sends an ARP response with its own MAC address to the client(9.5.4.23). Here our client gets the MAC to address of its gateway & ready to send the outbound packet. The operating system opens an ephemeral port suppose 51355 and opens a socket connecting the browser through this port.

The networking stack starts to form TCP segment. It completes all the header field like source port (51355) and destination port(80), sequence number filled, SYN flag is assigned to 1 and finally, the checksum is calculated and filled in the corresponding checksum field. This TCP segment is now given to the IP layer of the networking stack. Here IP header is filled with source IP 9.5.4.23 and destination IP 125.5.45.34, Time to leave or TTL is set to 64. Now the earlier formed TCP segment is put as payload for IP datagram. Then checksum is calculated and filled. Now comes the turn of Ethernet frame all its field like source and destination MAC address are filled & then IP datagram formed earlier is inserted as the payload of ethernet frame and checksum value is calculated and filled.

Now it is ready to be sent to across the physical layer.It is sent through the wire connecting the client and the switch. The switch receives it & it already knows where this MAc address is which finally sends all the entire Ethernet frame to the router.

After this router does the following task:

Receives frame
Recognise address
Calculate checksum
Compare checksum
Match detected

Following these tasks, it then removes the Ethernet frame with the only datagram left & then performs a checksum again to ensure the correctness of data. It then searches it Routing table and finds the destination IP address125.5.45.34 is connected via the local network. Now it decrements the TTL field by one (now 63) calculate the new checksum and makes new IP datagram which is again encapsulated by ethernet frame with destination and source MAC address filled which is finally sent to the Network B where the switch identifies the destination mac address and send it to the server.
This is the complete process of one-time connection with SYN field set to 1.This process is again repeated from the server side with ACK (Acknowledgement) set to one. These processes repeated again and again until the data is completely sent and a connection is closed.

Note ------ Do not copy it. Just to understand how to do a Peer-graded assignment.