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Chapter 1- An Introduction to Networking
Objectives:
● Identify types of applications and protocols used on a network ● Distinguish between the client-server and peer-to-peer models used to control access to a network ● Describe various networking hardware devices and the most common physical topologies ● Describe the seven layers of the OSI model
Computer Network
● A group of computers and other devices (such as Printers) that are connected by some type of transmission media ● A network can be as small as two computers connected by a cable or as largest as the Internet ● Networks may link – cell phones, personal computers, printers, fax machines, and phone systems ● Networks might communicate through copper wires, fiber-optics cable, or radio waves
How Networks are Used
● Network services - the resources a network makes available to its users ● Includes applications and the data provided by these applications ● Types of applications found on most networks: ● Client-Server ○ Client computer requests data or a service from a second computer, called the server. ○ How does a client know how to make a request in a way the server can understand and respond to? ○ The networked devices use protocols- the methods and rules for communication ○ List of several popular client-server applications: ■ Web service ● A client requests a web resource from the web server. ● Web servers could be privately hosted in a corporation or could be public. ● A client is a browser on the computer and uses HTTP (Hypertext Transfer Protocol) to communicate with the server. ● When HTTP is combined with an encryption protocol e.g. SSL (Secure Socket Layer) or TLS (Transport Layer Security), the protocol becomes HTTPS (HTTP Secure) ■ Email services ● This involves two servers. ● The sender (client) uses SMTP(Simple Mail Transfer Protocol) to send an email message to the first server. ● The first is called as SMTP server. ● The SMTP server sends message on to the receivers mail server. ● The recipient mail server delivers the message to the receiving client using one of the two protocols: ● POP3 (Post Office Protocol version 3) – downloads to client computer. ● IMAP4 (Internet Message Access Protocol version 4) – Manages email stored on the mail server ■ FTP service ● Transfers Files between two computers ● Uses File Transfer Protocol ● FTP does not provide encryption, therefore? ● You can use web browsers to connect to FTP servers ● There FTP client applications with more features. ○ E.g. CuteFTP ● Search on internet popular FTP client applications ● Encrypted and Secure version of FTP is called SFT
■ Telnet service ● Telnet protocol (command) is used by administrators or users to remote in or control a computer remotely. ● Is included in my operating systems ● Not secure ● Secure Shell(SSH) is secure version of telnet used in linux. ● SSH creates a secure channel between two computers. ■ Remote Desktop ● This is windows application ● Uses Remote Desktop Protocol ● Provides secure, encrypted transmission to remote in a computer ■ Remote applications ● The applications are installed and executed on a server. ● Presented to a user working at a client computer. ● Windows server 2008 and later provide remote application services. ● Secure and stable. ● File and Print Services ○ File services - a server’s ability to share data files and disk storage space ○ File server - a computer that provides file services ○ Print services - ability to share printers across a network ■ With one printer, less time is spent on maintenance and management ● Communications Services ○ Convergence - using the same network to deliver multiple types of communications services ■ Such as Video, Voice, Fax etc. ○ Three types of communication services: ■ Conversational voice - VoIP (Voice over IP) ● Allows two or more people to have voice conversation. ● When only two people are having conversation, it uses point-to point model. ● Computers used for conference call uses point-to-multipoint model ■ Streaming live audio and video ● Uses client server model, one server and many clients ● Also called multicast distribution ■ Streaming stored audio and video: e.g? ○ Voice and video transmissions are delay-sensitive ■ You don’t want to hear or see breaks in transmission or buffering. ○ Voice and video transmission are considered loss-tolerant: occasional data lost can be tolerated. ○ Network administrators must pay attention to the quality of service (QoS) a network provides for voice and video ● Bandwidth - the amount of traffic, or data transmission activity, on the network
Controlling Network Access
● Topology - how parts of a whole work together ● Physical topology - mostly applies to hardware and describes how computers, other devices, and cables fit together to form the physical network ● Logical topology - has to do with software and describes how access to the network is controlled ○ How users and programs initially gain access to the network ○ Giving access to Network is a function of operating systems. ○ Each OS can be configured to use either of the two models ■ Peer-to-Peer (P2P) network model ● The OS of each computer on the network is responsible for controlling access to its
Local Area Networks (LANs) and Their Hardware
● Usually contained in a small space like an office or building ● Switch - receives incoming data from one of its ports and redirects it to another port or multiple ports ○ Will send the data to its intended destination ● Star Topology- all devices connected to one central device (usually a switch) ● Onboard Network Port- Embedded in computers motherboard. ● Network interface card (NIC) - a network port used to attach a device to a network. ● NIC- also called as Network Adapter, installed ion expansion slot of the motherboard. ● Can have several switches ● Backbone - a central conduit that connects the segments (pieces) of a network ○ Might use higher transmission speeds and different cabling than network cables connected to computers ● When a LAN needs to communicate with another network, it needs a device called Router. ● Router - a device that manages traffic between two or more networks ○ Can help find the best path for traffic to get from one network to another ● Routers can be used in small home networks to connect the home LAN to the Internet ● Industrial-grade routers can have several network ports, one for each network it connects to ● Difference between router and switch: Router is like a gateway between networks
Metropolitan and Wide Area Networks (MANs and WANs)
● Metropolitan area network (MAN) - a group of connected LANs in the same geographical area ○ Also known as a campus area network (CAN) ● WAN (wide area network) - a group of LANs that spread over a wide geographical area ● Internet is the largest and most varied WAN ● MANs and WANs often use different transmission methods and media than LANs
Personal Area Network (PAN)
● Smallest network ● A network of personal devices
The Seven-Layer Open Systems Interconnection (OSI) Model
● a seven-layer model developed to categorize the layers of communication ● Designed by ISO in the 1980’s ● Layer 7: Application Layer ○ Describes the interface between two applications, on separate computers ○ Application layer protocols are used by programs that fall into two categories: ■ Provide services to a user, such as a browser and Web server ■ Utility programs that provide services to the system, such as SNMP that monitor and gather information about network traffic ○ Payload - data that is passed between applications or utility programs and the OS
● Layer 6: Presentation Layer ○ Responsible for reformatting, compressing, and/or encrypting data in a way that the receiving application can read ■ Example: An email message can be encrypted at the Presentation layer by the email client or by the OS ● Layer 5: Session Layer ○ Describes how data between applications is synched and recovered if messages don’t arrive intact at the receiving application ○ The Application, Presentation, and Session layers are intertwined ■ Often difficult to distinguish between them ○ Most tasks are performed by the OS when an application makes an API call to the OS ■ Application programming interface (API) call is the method an application uses when it makes a request of the OS ● Layer 4: Transport Layer ○ Responsible for transporting Application layer payloads from one application to another ○ Two main Transport layer protocols are: ■ TCP (Transmission Control Protocol) - makes a connection with the end host, checks whether data was received; called a connection-oriented protocol. ■ UDP (User Datagram Protocol) - does not guarantee delivery by first connecting and checking whether data is received; called a connectionless protocol. ○ Protocols add their own control information in an area at the beginning of the payload (called a header) ○ Encapsulation - process of adding a header to the data inherited from the layer above ○ The Transport layer header addresses the receiving application by a number called a port number ○ If message is too large, TCP divides it into smaller messages called segments ■ In UDP, the message is called a datagram ● Layer 3: Network Layer ○ Responsible for moving messages from one node to another until reaches destination ○ IP(Internet Protocol) adds its own Network layer header to the segment or datagram ■ The entire Network layer message is called a packet. ■ The header identifies sending and receiving hosts by their IP addresses. ○ IP address - assigned to each node on a network ■ Network layer uses it to uniquely identify each host ○ IP relies on several routing protocols to find the best route for a packet to take to reach destination ■ ICMP(Internet Control Message Protocol) and ARP (Address Resolution Protocol) are examples. ○ If a packet is larger than maximum size for its network, the packet is divided into smaller packets called as fragments. ● Layer 2: Data Link Layer ○ Layers 2 and 1 are responsible for interfacing with physical hardware on the local network ■ Protocols at these layers are programmed into firmware of a computer’s NIC and other hardware ○ Type of networking hardware or technology used on a network determine the Link Layer protocol used ■ Ethernet and Wi-Fi are examples ○ The Link layer puts control information in a Link layer header and at the end of the packet in a trailer ■ Entire Link layer is called a frame. ■ The frame header contains hardware addresses of the source and destination NICs. ○ MAC (Media Access Control) address- hardware address of the source and destination NICs ■ Also called a physical address, hardware address, or Data Link layer address ■ Embedded on every network adapter and are considered short-range addresses that can only find nodes on the local network ● Layer 1: Physical Layer
Question 1 A standard network switch operates at what layer of the OSI model? a. Layer 2 b. Layer 7 c. Layer 5 d. Layer 3 Question 2 Any computer or device on a network that can be addressed on the local network is referred to as a: a. node b. subject c. host d. target Question 3 At what layer of the OSI model do the IP, ICMP, and ARP protocols operate? a. Application b. Session c. Transport d. Network Question 4 HTTP, IMAP4, FTP, and Telnet are all examples of protocols that operate at what layer of the OSI model? a. Layer 6 b. Layer 5 c. Layer 4 d. Layer 7 Question 5 If a Network layer protocol is aware that a packet is larger than the maximum size for its network, it will divide the packet into smaller packets in a process known as: a. framing b. fragmentation c. packet splitting d. de-encapsulation Question 6 In what network topology are devices daisy-chained together in a single line? a. bus topology b. star topology c. ring topology d. star bus topology Question 7 Select the layer of the OSI model that is responsible for reformatting, compressing, and/or encrypting data in a way that the application on the receiving end can read: a. Session b. Presentation c. Transport d. Application Question 8
The process of adding a header to the data inherited from the layer above is called what option below? a. encapsulation b. segmenting c. appending d. fragmenting Question 9 The segment or datagram protocol data unit exists at what layer of the OSI model? a. Data link layer b. Transport layer c. Application layer d. Network Layer Question 10 What are the two main Transport Layer protocols? a. IPX b. SPX c. TCP d. UDP Question 11 What layer of the OSI model describes how data between applications is synced and recovered if messages don't arrive intact at the receiving application? a. Transport Layer b. Session Layer c. Presentation Layer d. Application Layer Question 12 What mail protocol is used to send mail messages to a server? a. SMTP b. IMAP c. HTTPS d. POP Question 13 What physical network topology consists of all connected devices connecting to one central device, such as a switch? a. bus topology b. ring topology c. star topology d. hub topology Question 14 What two encryption protocols are commonly used with the Hypertext Transfer Protocol? a. AES b. TLS c. SSL d. SSH Question 15 What two mail delivery protocols below can be used by a client application to receive e-mail from a server? a. POP b. SMTP c. MGET d. IMAP
● e.g. web server is usually configured to listen incoming requests at port 80. ■ There are dedicated port numbers and user defined. ○ At Network Layer: ■ This layer uses IP addresses to find the destination computer on a network. ■ Internet Protocol addresses are assigned to each interface on a network. ● e.g. you may more than one network adapter installed on your PC. Each network adapter is assigned its own IP address ■ Two types of IP addresses are: ● IPv ○ consists of 32 bits and represents 4 octets. ○ Uses 32-bit addresses which limits the address space to 4294967296 (2^32 ) addresses. ● IPv ○ Since these address space is limited, therefore, IPv6 came into existence. ○ consists of 128 bits. ○ represented as eight groups of four hexadecimal digits with the groups being separated by colons ○ •Allowing 2^128 , or approximately 3.4×1038 addresses. ○ •The total number of possible IPv6 addresses is more than 7.9×10^28 times as many as IPv ○ At Data Link Layer ■ Every Network Adapter has a MAC address, also called as a physical address. ■ Consists of 48 bits. ■ First 24 bits are known as the OUI (Organizationally Unique Identifier) or block ID or company- ID (Assigned by IEEE) ■ Last 24 bits make up the extension identifier or device ID. ● Manufacturer’s assign each NIC a unique device ID ● Based on the Model number and the Date. ■ What are MAC addresses used for? ■ https://www.howtogeek.com/169540/what-exactly-is-a-mac-address-used-for/
How Host Names and Domain Names Work
● If you have to communicate with a computer on a network you need an IP address. ● But remember IP addresses are difficult. ● Character-based names are easier to remember. ○ e.g byteknights.msmc.edu is easier to remember than its IP address. ● Last part of an FQDN is called the top-level domain (TLD) ○ In this case TLD is .edu ● Domain names must be registered with an Internet naming authority that works on behalf of Internet Corporation of Assigned Names and Numbers(ICANN) ○ ICANN restricts what type of hosts can be associated with .arpa, .mil, .int, .edu, and .gov ● Applying for new TLDs cost $185000 and each application goes rigorous processing ● Name resolution: ○ The process of discovering the IP address of a host when you know the FQDN.
○ On a local Network, host name resolution works using host files. ○ On the Internet, host name resolution works differently.
Domain Name System
● An Application layer client-server system of computers and databases made up of these elements: ● namespace - the entire collection of computer names and their associated IP addresses stored in databases on DNS name servers around the globe ● name servers - hold databases, which are organized in a hierarchical structure ● resolvers - a DNS client that requests information from DNS name servers
How Name Servers are Organized
● DNS name servers are organized in a hierarchical structure ● At the root level, 13 clusters of root server hold information used to locate top-level domain (TLD) servers ● TLD servers hold information about authoritative servers ● The authority on computer names and their IP address for computer in their domains
Recursive and Iterative Queries
● Two types of DNS requests: ○ Recursive - a query that demands a resolution or the answer “It can’t be found” ○ Iterative - a query where the local server issues queries to other servers ■ Other servers only provide information if they have it ■ Do not demand a resolution
DNS Zones and Zone Transfers
● DNS follows a distributed database model
■ Class B ● Was for the first two octets. ○ A company that leased a class B license 150.100 acquired 150.100.0.0.0 to 150.100.255.255 IP addresses ■ Class C ● Class C license was for the first three octets. ○ A company that leased a class C license 200.80.15 acquired 200.80.15.0 to 200.80.15.255 IP addresses ■ Class D ● Class D is not available for general use ○ Class D begin with 224-239 and are used for multicasting. ○ In multicasting, one hosts sends message to multiple hosts e.g. videoconferencing. ■ Class E ● Class D is not available for general use ○ Class E begin with octets 240-254 and are used for research. ○ Also, block of addresses that begin with 127 are reserved for research. ○ When class licenses were available from IANA: ■ A company could lease a class A, class B or Class C license ■ Acquiring multiple IP addresses in a class license. ● IPv ○ Since these address space is limited, therefore, IPv6 came into existence. ○ consists of 128 bits. ○ represented as eight groups of four hexadecimal digits with the groups being separated by colons ○ Allowing 2^128 , or approximately 3.4×1038 addresses. ○ The total number of possible IPv6 addresses is more than 7.9×10^28 times as many as IPv ○ IPv6 were developed to: ■ Improve routing capabilities ■ Speed of communication over IPv ■ Allow more public IP addresses on the internet. ○ An IPv6 address has 128 bits written as eight blocks of hexadecimal numbers separated by colons ■ Ex: 2001:0000:0B80:0000:0000:00D3:9C5A:00CC
■ Each block is 16 bits ■ Leading zeros in a four-character hex block can be eliminated ■ If blocks contain all zeroes, they can be written as double colons (::), only one set of double colons is used in an IP address ■ Therefore, above example can be written: ● 2001:0000:B80::D3:9C5A:CC ○ Terminology: ■ Link (sometimes called local link)- any LAN bounded by routers ● An interface is a node’s attachment to a link ■ Tunneling- a method used by IPv6 to transport IPv6 packets through or over an IPv4 network ■ Interface ID- the last 64 bits or four blocks of an IPv6 address that identify the interface ■ Neighbors- two or more nodes on the same link ○ Autoconfiguration ■ IPv6 addressing is designed so that a computer can autoconfigure its own link local IP address with the help of DHCP server ● Similar to how IPv4 uses an APIPA address ■ Step 1 - The computer creates its IPv6 address ● Uses FE80::/64 as the first 64 bits ● Last 64 bits can be generated in two ways depending upon how OS is configured: ○ Randomly generated ○ IP address is called temporary address and is never registered in DNS or used to generate global address for internet. ○ The IP address changes often to help prevent hackers from discovering the computer. ○ Default method used by Windows 7 and Windows 8 ○ Generated from the network adapter’s MAC address ■ MAC addresses consists of 48 bits. ■ Must be converted to 64 bit standard – This is called as Extended Unique Identifier 64(EUI-64) ■ To generate Interface ID- ● OS takes 48 bits of the device’s MAC address ● Inserts fixed 16 bit value in the middle of 48 bits between OUI and NIC portion. ● Inverts the value of the seventh bit. ■ Step 2 - The computer checks to make sure its IP address is unique on the network ■ Step 3 - The computer asks if a router on the network can provide configuration information ● If a router responds with DHCP information, the computer uses whatever information this might be ○ Such as the IP addresses of DNS server or the network prefix ● If the network prefix is supplied, this will become the first 64 bits of its own IP address. Process is called prefix discovery
Types of IP Addresses
● Unicast address - specifies a single node on a network ○ Global unicast address - can be routed on the Internet ■ Also called global address ■ Similar to public IPv4 addresses. ■ Most Global addresses begin with prefix 2000::/ ■ The /3 indicates, the first 3 bits are fixed and are always 001 ■ 16 bits is subnet ID. ■ Subnet is a smaller network on a larger network. ○ Link local unicast address - can be used for communicating with nodes in the same link. ■ Also called a link local address. ■ These addresses are similar to IPv4’s autoconfigured APIPA addresses. ■ Begin with FE80::/ ■ The first 10 bits must be followed another 54 zero’s to make it 64 bits for the network portion of the address.
○ Dynamic Network Address Translation (DNAT)- the gateway has a pool of public address that it is free to assign to a local host when it makes a request to access the Internet
Tunneling
● Dual stacked- term given when a network is configured to use both IPv4 and IPv6 protocols ● If packets on this network must traverse other networks where dual stacking is not used, tunneling is used ● Three tunneling protocols: ○ 6to ○ ISATAP (Intra-Site Automatic Tunnel Addressing) ○ Teredo
Chapter 2 Quiz Review
Question 1 A loopback IP address begins with what number? a. 127 b. 254 c. 169 d. 192 Question 2 A port number, which identifies an application on a host, exists at what level of the OSI model? a. Network b. Transport c. Data link d. Application Question 3 An IPv6 address consists of how many bits? a. 48 b. 96 c. 128 d. 32 Question 4 How many clusters of root servers exist? a. 13 b. 10 c. 8 d. 15 Question 5 In Linux systems, what file contains the settings for the DHCP service? a. dhcp.ini b. dhcpd.conf c. dhcp.cf d. dhcpd.cfg Question 6 Select the IPv6 address below that indicates a global unicast address: a. FD00::/ b. 2000::/ c. FC00::/ d. FE80::
Question 7 Select the name of the free, open source software that is by far the most popular DNS server software: a. Microsoft DNS b. BIND c. Dnsmasq d. Oracle Resolver Question 8 Traditional MAC addresses are broken into two parts. Name these two parts. a. primary octet b. device ID c. block ID d. secondary octet Question 9 What are the last two parts of a host name known as? a. host qualifier b. top level domain c. domain name d. fully qualified domain name (FQDN) Question 10 What command below can be used to display a complete summary of all network interfaces in a Windows computer? a. ipconfig /list b. ipconfig /show c. ipconfig /a d. ipconfig /all Question 11 What command on Linux will display TCP/IP information associated with every interface on the device? a. ipconfig -a b. ipconfig /all c. ifconfig /all d. ifconfig -a Question 12 What do the first 24 bits of a MAC address represent? a. extension ID b. network ID c. Organizationally Unique Identifier d. device ID Question 13 What range of ports is referred to as the "well-known" range of ports? a. 0- b. 49152- c. 500 - 1024 d. 1024- Question 14 What two address prefixes for IPv6 addresses are used for unique local unicast? a. FD00::/ b. FE80::/ c. FC00::/ d. FF00::/
The IP addresses 169.254.0.1 and 169.254.255.254 are both examples of Automatic Private IP Addressing (APIPA). Question 24 The MAC address, which is also known as the physical address, is embedded on every NIC and is assumed to be unique. Question 25 A hexadecimal number is a number written in the base 16 number system. True Question 26 DNS follows a centralized database model. False Question 27 Each organization that provides host services on the public Internet is responsible for providing and maintaining DNS authoritative servers for public access. True Question 28 ICANN is responsible for restrictions on use of the .com, .org, and .net TLDs. False Question 29 ● A protocol that runs in the Session and Transport layers of the OSI model and associates NetBIOS names with workstations. NetBIOS ● The nonprofit corporation currently designated by the U.S. government to maintain and assign IP addresses. Internet Corporation for Assigned Names and Numbers (ICANN) ● A type of DNS data record that maps the IPv4 address of an Internet-connected device to its domain name. A (Address) record ● A type of DNS data record that is used for reverse lookups, to provide a host name when the IP address is known. PTR (Pointer) record ● A type of address translation in which a gateway assigns the same public IP address to a host each time it makes a request to access the Internet. Static Network Address Translation (SNAT) ● A unique set of characters assigned to each NIC by its manufacturer. In the traditional, 48-bit physical addressing scheme, the extension identifier is 24 bits long. In EUI-64, the extension identifier is 40 bits long. device ID ● A type of address translation in which a gateway has a pool of public IP addresses that it is free to assign to a local host whenever the local host makes a request to access the Internet. Dynamic Network Address Translation (DNAT) ● A service available on computers running one of the Windows operating systems that automatically assigns the computer's network interface a link-local IP address. In IPv4, this address is in the range of 169.254.0.1 through 169.254.255.254. Automatic Private IP Addressing (APIPA) ● A type of DNS data record that maps the IPv6 address of an Internet-connected device to its domain name. AAAA (Address) record ● A software package or hardware-based tool that can capture and analyze data on a network. packet analyzer
Chapter 3- How Data is Transported Over Networks
Objectives:
● Identify and explain the functions of the core TCP/IP protocols ● Explain the purposes and properties of routing and describe common IPv4 and IPv6 routing protocols ● Employ multiple TCP/IP utilities for network discovery and troubleshooting
Transmission Control Protocol/Internet Protocol Core Protocols
● TCP/IP means is is a protocol for communications between computers, used as a standard for transmitting data over networks and as the basis for standard Internet protocols. ● TCP/IP - a suite of protocols including: TCP, IP (IPv4 and IPv6), UDP, ARP, and many others ● TCP/IP is open (a company does not need a license to use it) ● TCP/IP is routable (routers can determine the best path for directing data over a network). Protocols add a header
to data inherited from the layer above it
What layers are necessary for transporting Data?
● Layers 7, 6, and 5 - Data and instructions, known as payload, are generated by applications running on source host ● Layer 4 - Usually TCP or UDP adds a header to the payload. Includes a port number to identify the receiving app. Entire message becomes a segment(For TCP) or datagram(For UDP) ● Layer 3 - Network layer adds it own header and becomes a packet. The header identifies an IP address of the destination host ● Layer 2 - packet is passed to Data Link layer on NIC, which encapsulates data with its own header and trailer, creating a frame ● Layer 1 - Physical layer on the NIC receives the frame and places the transmission on the network ● Receiving host de-encapsulates the message at each layer in reverse order (Layer 1, Layer 2, 3, 4, 5 Layer 5, 6, and 7) and presents payload to the receiving applications ● Connectivity devices are specialized devices that allow two or more networks or multiple parts of one network to connect and exchange data. Such as Switches, Routers. A device is Known by the highest OSI layer they read and process
Transmission Control Protocol (TCP)
● TCP operates in the Transport layer of OSI model ● Provides reliable data delivery. ● Three characteristics of TCP ○ Connection-oriented protocol – ■ Before TCP transmits data, it ensures that a connection or session is established. ■ TCP uses a three-step process called a three-way handshake to establish a TCP connection. ○ Sequencing and checksums – ■ This is used to make sure that the other end is receiving the message correctly. ■ Sequencing is to add a sequence to every packet sent, the checksum checks that the sequence on the receiving computer is correct and receives all packets. ■ TCP sends a character string called a checksum ■ TCP on the destination host then generates a similar string. ■ If the two checks failed to match, the destination host asks the source to retransmit the message ■ These messages won’t necessarily arrive in the same order as they were sent, TCP attaches a chronological sequence number to each segment sent by the source to reorder at the destination. ○ Flow control - gauges rate of transmission based on how quickly recipient can accept data. Is the process of gauging rate of transmission based on how quickly recipient can accept data. ■ For example, suppose a server indicates its buffer can handle up to 4000 bytes at a time. ■ Suppose the client has already issued 1000 bytes, 250 of which have been received and acknowledged by the server. ■ That means that the server is still buffering 750 bytes. ■ The client can only issue 3250 additional bytes before it receives acknowledgment from the server for the 750 bytes.
