Question 9 (Section 5.12.1): (self-learning, ARP, DNS, TCP, and HTTP) Suppose no

Question

Question 9 (Section 5.12.1):

(self-learning, ARP, DNS, TCP, and HTTP)

Suppose no frames have been sent in the LAN for a long time so all tables are empty. Now suppose that the host with IP address 10.0.0.1 wants to request a web page from the Google server, where the web page can be contained in a single TCP segment. Detail which packets are sent and the impact on the various tables for each packet. Use one worksheet for each packet or frame sent. Do this up to the third IP packet sent by the host. (Hint: save the worksheet to disk. Open the worksheet in PowerPoint. As tables are filled

Ethernet Frame:lype= Source= IP packet (if appropriate): Source- TCP packet (if appropriate). Source Port HI iP request line (If appropriate) HTTP header line (if appropriate) HTTP header line (if appropriate) HI P header line (f appropriate) HTTP header line (if appropriate) Description Destination= Destination Destination Port= TCP Flags that are set- MAC Forwarding Table MAC Forwading Table ARP Table ARP Tahle Google server IP: 201.1.2.3 MAC Interface MACInterface MAC IP MACIP 3 2 internet gateway P: 10.1.2.1 MAC: 22:22:22:22:22 2 End-host IP: 10.1.2.3 MAC: 11:11:11:11:11 interface MAC Forwarding Table DNS Server IP. 10.1.2.4 MAC: 33:33:33:33:33:33 MACInterface

Explanation / Answer

For my machine to communicate with others (the gateway in this case), it may need to do an ARP Broadcast (if it doesn't already have the MAC address in the ARP cache)

It then needs to resolve google.com's IP address. It does this by contacting the DNS server. (I'm not completely sure how it knows where the DNS server is? Or is it the gateway that knows?)

This involves communication through the TCP protocol since HTTP is built on it (TCP handshake: SYN, SYN/ACK, ACK, then requests for content, then RST, RST/ACK, ACK)

To actually load a webpage, the browser gets the index.html, parses it, then sends more requests based on what it needs? (images,etc)

And finally, to do the actual google search, I don't understand how the browser knows to communicate "I typed something in the search box and hit Enter".

In this case you would broadcast the ARP request in the LAN until someone responds to you. This could be the router or any other device connected to the switch.

It then needs to resolve google.com's IP address. It does this by contacting the DNS server. (I'm not completely sure how it knows where the DNS server is? Or is it the gateway that knows?)

If you use DHCP, then that has already provided you with the IP of the DNS server. If not, then it means that you manually provided the IP of the DNS. So the IP of the DNS server is stored locally on your computer.

Making a DNS request is just about putting its IP in the packet with the request and forwarding the packet to the network.

Sidenote: DHCP also provides the IP address of the router.

This involves communication through the TCP protocol since HTTP is built on it (TCP handshake: SYN, SYN/ACK, ACK, then requests for content, then RST, RST/ACK, ACK)

Yes. To clarify things: When your computer sends the request

The frame is being sent to your LAN's switch which forwards it to the MAC of the router. Your router will open the frame to check the destination IP and route it accordingly(in this case to the WAN). Finally when the frame arrives at the server, the server will open the TCP segment and read the payload, which is the HTTP message. The ACK/SYN etc. messages are being processed just by your computer and the server and not any router or switch.

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