Friday, September 3, 2021 10:34 AM

example
All open on one computer:
Port 80 Web ServerPort 800 Ad Server
Port 9876 Wire Application
Socket
  • Includes IP address, transport protocol, and port number
  • (10.1.1.2, TCP, port 80)

Multiplexing

  • 0 to 1023

Well Known (System) Ports:

  • 1024 to 49151

User (Registered) Ports:

  • 49152 to 65535,
  • not assigned
      • uses the same port number for all connections. For example, web server with 100 clients would have only one socket (one port number)
    • server looks at source port of received TCP segments.
  • Servers use well-known ports (or user ports), whereas clients use dynamic ports

Ephemeral (Dynamic, Private) Ports:

Popular TCP/IP Applications
Simple Network Management Protocol (SNMP)

    • query, compile, store, and display information about a network’s operationCisco Prime software
      FTP/ TFTP
  • FTP allows many more features
  • TFTPis very simple, good tools for embedded parts of networking devices.
    SMTP/ POP3
  • Simple Mail Transfer Protocol (SMTP) and Post Office Protocol version 3 (POP3)
  • both used for transferring mail (TCP).
    Port numbers and protocols

Port numbers and protocols

    • FTP Data TCP 20FTP Control TCP 21
    • SSH TCP 22Telnet TCP 23
  • SMTP TCP 25
    • DNS UDP/TCP 53DHCP Server UDP 67
    • DHCP Client UDP 68TFTP UDP 69
    • HTTP TCP 80POP2 TCP 110
  • SNMP UDP 161
    • SSL TCP 443Syslog UDP 514

Connection Establishment and Termination

▪▪ SYN, DPORT=80, SPORT=49145SYN ACK , DPORT= 49145, SPORT=80
▪ ACK DPORT=80, SPORT=49145
    • initializing Sequence and Acknowledgment fields agreeing on the port numbers
  • 2 bits inside the flag fields of the TCP header. Called the SYN and ACK flags
TCP connection establishment (3 way handshake) occurs 1st
TCP connection termination. (four-way)
▪▪ ACK, FIN >< ACK
▪▪ ACK, FIN << ACK
  • uses an additional flag, called the FIN bit

Error Recovery and Reliability

    • reliability in both directionsSequence Number field of one direction and Acknowledgment field in the other direction - 1000 bytes, Seq = 1000 > - - 1000 bytes, Seq = 2000 >1000 bytes, Seq = 3000 > - < no data, ACK = 4000
      ▪ received all data with sequence numbers up through one less than 4000
      ▪ ready to receive your byte 4000 next.
    • ack by listing the next expected byte (forward acknowledgment)sequence number field identifies the data (sender)

  • forward acknowledgments acknowledge the data (receiver)

  • forward acknowledgments acknowledge the data (receiver)

      • ask the sending host to resendacknowledge that the re-sent data arrived

  • Sequence and Acknowledgment fields let the receiving host can notice lost data

      • 1000 bytes, SEQ 1000 >1000 bytes, SEQ 2000 X>
    • 1000 bytes, SEQ 3000 >
      □ (received 1000 -1999 and 3000 -3999, asking for 2000)
    • < no data, ACK = 2000
    • 1000 bytes, SEQ 2000 >
    • < no data, ACK 4000
    • Sender may wait a few moments to make sure no other acknowledgments arrive
    • Retransmission timer

Flow Control Using Windowing
Sliding window (dynamic window- Receiver slides the window size up and down

    • < ACK=1000, Window=3000SEQ=1000, SEQ=2000, SEQ=3000 >
  • < ACK=4000, Window=4000
    User Datagram Protocol
  • connectionless
    • no reliability, no windowing,
    • no reordering of the received data, andno segmentation of large chunks of data into the right size for transmission
    • provides data transfer and multiplexing using port numbersLess overhead and processing than TCP.
  • no reordering or recovery
  • DNS requests use UDP, user will retry an operation if the DNS resolution failsNetwork File System (NFS), a remote file system application, performs recovery with
    application layer code, so UDP features are acceptable to NFS.
-
    • Source port, Destination PortLength, Checksum
  • 8 byte header
Uniform Resource Identifiers (URI)
    • clicking a link and typing a URIreferred to as web address or Universal (uniform) Resource Locator [URL]—refer to a URI
  • three key components
    • before the :// identifies the protocol
      • between the // and / identifies the server by nameafter the / identifies the web page.

TCP/IP Applications

  • http:// (Scheme)
    • < Name Resolution Request (IP Header, UDP Header, DNS Request)Name resolution Reply (Ip Header, UDP Header, DNS Request (IP address) >
  • < TCP connection to requested web server
    • DNS requests can be cached by hosts and serversLocal DNS may need to ask for help
  • Sends repeated DNS messages to find the authoritative DNS server.
➢➢ Root DNS .com TLD DNS
➢ Authoritative cisco.com DNS
  • Recursive DNS lookup- host > Enterprise DNS >
  • The enterprise DNS acts as a recursive DNS server
DNS
  • HTTP GET request lists file it needs
    • HTTP GET response from server with a Server may issue areturn code of 404, (file not found)return code of 200 (meaning OK) and file’s contents.
  • Web pages consist of multiple files, called objects
  • Objects are stored as different files on the web serverWeb browser gets the first file which can include references to other URIs that the browser
    also requests
-
    • < HTTP GET /go/ccnaHTTP OK data >
  • < HTTP GET /graphics/logo1.gif
    • HTTP OK data >< HTTP GET /graphics/ad1.gif
  • HTTP OK data >
    • Flow over one or more TCP connection between the client and the server.

Transferring Files with HTTP

Identifying the Correct Receiving Application

  • tracks which port opened which request

Fields that identify next header
< Ethernet (Type) (0x0800)
< IPv4 (Protocol) (6)< TCP (Destination port) (49124)