Flashcards in Chapter 1: Networking Protocols Deck (151)
What are the four layers of the TCP/IP model?
- Internet (Networking)
What are the two layers of the Link layer?
- Data Link
- provides physical transmission support and includes the protocols used to transmit information over a link between two devices
- includes hardware and protocol necessary to send information between two hosts that are connected by a physical link (cable) or over the air (radio waves)
- Most popular protocol is Ethernet
- aka Networking
- provides networking services and includes protocols that allow for the transmission of information through multiple hops
- each "hop device" knows how to reach the destination IP address and transmit the information to the next best node to reach the destination
- the way each node (router) determines the best next node to the destination
- when transmitting information, the sending host knows when the information is sent, but has no way to know whether it actually made it to the destination
- so, Transport Layer provides services to successfully transfer information between two end-to-end process
- detects whether any information went missing
- provides information about which type of information is being transmitted
How does the Transport Layer distinguish between separate transactions, such as requesting a web page and starting an FTP transaction?
- the Transport Layer helps to separate the two requests by using the concept of a Transport Layer PORT
- port 80 for web request
- port 21 for an FTP transaction
- this service is called MULTIPLEXING
- top layer and most familiar to end users
- a user may use the mail client to send an email message (SMTP), or use a web browser to browse a website (HTTP)
TCP/IP Model Encapsulation
- each layer provides services for the level above it
- protocols at each layer include a protocol header
- the header includes enough information for the protocol to work toward the delivery of the information
- this process is called ENCAPSULATION
Step 1: Host A sends a recursive DNS query for a type A record to resolve www.cisco.com to its own DNS server (DNS A)
Step 2: DNS A server checks its DNS cache, but does not find the information. So, it sends an iterative DNS query to the root DNS server, which is authoritative for all of the Internet
Step 3: The root DNS server is not authoritative for that host, so it sends back a referral to the .com DNS server, which is authoritative server for the .com domain.
Step 4: The .com DNS server performs a similar process and sends a referral to the cisco.com DNS server
Step 5: The cisco.com DNS server is the DNS authoritative server for www.cisco.com so it can reply to DNS A with the information
Step 6: DNS A receives the information and stores it in its DNS cache for future use.
Step 7: Host A receives the information from DNS A and can start sending packets to www.cisco.com using the correct IP address.
How long does a DNS server store information in its cache?
- finite time based on the TTL value in the response from the authoritative DNS server for a given doamin
- Transmission Control Protocol
- reliable, connection-oriented protocol for communicating over the Internet
- Connection-oriented means that TCP requires a connection between two hosts established through a specific packet exchange before any data packets can be sent
- connection establishment and termination
- reliability (error detection and recovery)
- flow control
Why not use TCP for all applications?
- the reliability offered by TCP is done at the cost of lower speed and the need for increased bandwidth
- allows multiple transport layer connections between the same hosts
- sockets are used to distinguish to which application a connection belongs
Connection Establishment and Termination
- a connection is established before data is sent
- this ensures that the other host is ready to receive data
- the connection is also terminated through a formal data exchange
- data lost due to error or from the underlying datagram can be recovered by asking the remote device to send the information again
- TCP uses a windowing system to adjust the speed of transmission
TCP Header Fields
- Source and Destination Ports
- Sequence Number
- Acknowledgment Number
- Control Flags
- Urgent Pointer
- Acknowledgement flag
- Set to 1 after the connection has been established
- Push flag
- signifies that the data should be pushed directly to an application
- Reset flag
- Resets the connection
- sequence numbers
- relevant for connection establishment
- should only be set within the first packets from both of the hosts
- this flag signifies that there is no more data from sender
- this field indicates the number of data bytes the sender of the segment is able to receive
- this field enables flow control
TCP Three-way Handshake
- First Packet (SYN): the client starts process of establishing a connection by sending a TCP segment that has the SYN bit set to 1. The client sends its initial sequence number X (random number chosen by client)
- Second Packet (SYN-ACK): the server responds with a SYN-ACK packet where it sends its own request for synchronization and its initial sequence number Y. Within the same packet, the server also sends the acknowledgment number X+1 (acknowledging the receipt of a packet with sequence number X, and requesting the next packet with sequence number X+1)
- Third Packet (ACK): the client responds with a final acknowledgment, requesting the next packet with the sequence number Y+1
What is the purpose of SYN from sender
- signals to the peer that it wants to synchronize the sequence numbers and establish the connection
- the client also sends its initial sequence number, which is random number chosen by the client
What are the steps of TCP/IP Model Encapsulation for a host requesting a web page using HTTP?
1. Host requests a web page using the HTTP application layer protocol. The HTTP application generates the DATA payload.
2. HTTP DATA payload send to the transport layer and a TCP header is created. The DATA payload and TCP header result in the TCP segment.
3. The Internet layer receives the TCP information, attaches an IP header, and encapsulates it in an IP Packet.
4. The IP packet is passed to the Data Link layer. An Ethernet header and trailer, and then transmits the Frame to the NIC, which will take care of the physical transmission of the frame.
- Standard for LLC (Logical Link Control)