Søk i Webskolen:

Globale linker

• Linker
• Oppgaver

Inet+

• Index
• Chapter 1
• Chapter 2
• Chapter 3
• Chapter 4
• Chapter 5
• Chapter 6
• Skilldrill
• På norsk

Tester

• 280 test
• 72 test
• 55 test

Braindumps

• Braindump1
• Braindump2
• Braindump3

Chapter 2 - Internet clients and Infrastructure

• Describe Internet clients and the infrastructure needed to support them
• Identify and explain desktop configuration issues
• Describe MIME types and components
• Identify legacy client problems
• Explain functionality of updates to client software
• Describe cookies and their advantages and disadvantages

Servers - The Network Operating System (NOS) is what turns a personal computer into a network server. Servers are computers that have been optimized to run a network operating system. NOS include: Novell NetWare and Windows NT server.

Workstations - a personal computer that is connected to a network. Also known as clients or stations.

Hosts - any device that has a TCP/IP address. A host can be a server, a workstation, printer, fax server, etc.

Types of networks

Legacy networks

• All processing takes place at the central computer
• Dumb terminals, which are terminals with no processing power, provide users access to the mainframe/minicomputer.
• Most applications are custom-built.

Peer-to-peer networks

• Each workgroup member acts somewhat like a server
• Workstations store their own application and data files.
• Processing occurs at the workstation level.
• Each workstation on the system talks to all of the other workstations.
• Allows for some level of file and printer sharing
• Limited security
• Integrated support in Windows 95/98/NT

Client/server networks

• Separate systems providing resources (servers) and accessing resources (clients).
• Resource and security management is fully centralized.
• Application and data files can be stored on the file server
• Files are downloaded to intelligent workstations (clients) for processing.
• Results are uploaded to the server for storage.

Hardware platforms

Hardware refers to the hardware physically tasked with handling data on the network. This hardware is made up of servers, workstations, Network Interface cards (NICs), cabling, hubs, routers and interconnecting devices of all types.

Hardware platforms include:

• IBM PCs or compatibles
• IBM RISC system/6000 and PowerPC series
• Sun microsystems
• SCO Unix on Intel or PowerPC processors
• WebTV
• Laptops
• PDAs

Multipurpose Internet Mail Extensions

E-mail, or electronic mail, is delayed messaging. Email is commonly sent using SMTP (Simple Mail Transfer Protocol) and received using POP (Post Office Protocol). Another mail format is IMAP, Internet Message Access Protocol. IMAP can be thought of as a remote mail access as you are reading messages that are stored on a central server versus being downloaded like when you use POP.

• MIME is an extension of the e-mail protocol.
• The e-mail protocol is part of the TCP/IP suite of protocols.
• MIME is used by e-mail, webservers and clients to format non-ASCII files of transmission over the Internet.
• MIME is used for e-mail attachments. A MIME header is prefixed to the file to indicate what type of file is being sent. The MIME header tells the receiving e-mail or browser client how to reconstruct the file properly.
• S/MIME uses public key encryption and certificates to secure e-mail from tampering.
  An e-mail sender distributes his/hers public key to those he/she needs to send messages to. The encryption information and a digital certificate is being sent with in the message body. If the recipient can unlock the e-mail using the public key, he/she knows the e-mail is valid. Only users who have a copy of the sender's public key can read the message.

Simple Mail Transfer Protocol

• SMTP is part of the TCP/IP protocol suite.
• Uses the well-known port 25
• SMTP is used to transport mail form one point to another on the Internet and between clients and servers.

Post Office Protocol 3

• POP3 is an e-mail server protocol used to distribute e-mail to mailboxes that users may download e-mail from.

Interactive Mail Access Protocol 4

• The IMAP4 protocol is an e-mail server protocol that makes an e-mail server function more like a file server.
• IMAP allows users to view and search through e-mail on the server without downloading the e-mail itself.
• E-mail can be archived on IMAP-servers.

TCP/IP and addressing

• TCP/IP is the protocol suite of the Internet. It provides a method for uniquely distinguishing sites and providing addresses for the sites.
• TCP/IP is based on the five layer architectural model, Department of Defense (DoD) reference model. This model has no equivalent to the OSI Presentation and Session layers.
  • Hardware Layer (Layer 1)
    • Is equivalent to the OSI Physical layer.
    • This is where physical aspects of transmitting and receiving packets are defined.
  • Network Interface (Layer 2)
    • Describes the physical connection medium between hosts.
    • Responsible for packet frame content over different interfaces and low-level protocols (SLIP, PPP, ISDN)
  • Internet (Layer 3)
    • Works like the OSI Network layer.
    • Is responsible for routing packets between different hosts and networks.
    • Included protocols: IP, ICMP, ARP, RARP, RIP and OSPF
  • Transport (Layer 4)
    • Also called Host-to-Host Service Layer.
    • Responsible for end-to-end integrity of data packets transmitted across the network and support options for both connection oriented and connection-less communication.
    • Protocols include: TCP, UDP.
  • Applications (Layer 5)
    • Also called Process Layer
    • Application protocols define the communication format between client and server process.
    • Includes support for applications like FTP, Telnet, SMTP, SNMP, DNS and NFS.

TCP/IP suite

All TCP/IP protocols are defined through Requests for Comments (RFCs).

• IP - provides packet routing and delivery between computer systems. It is connectionless, and cannot guarantee delivering.
• TCP - provides acknowledged, connection-oriented communications. Guarantees delivery, proper sequencing and data integrity checks.
• ICMP is used to control and manage information transmitted using TCP/IP. Also helps to reroute messages when a route is busy or has failed.
• ARP/RARP are used on LANs to enable hosts to translate IP addresses to the low-level MAC addresses that are needed to communicate at the Data Link level.
  ARP is used to request a station's MAC address when only the IP address is known.
  RARP is used when the MAC address is known, but not the IP address.
• UDP is designed for connectionless, unacknowledged communications.
• Telnet is a connectivity utility. It is a simple remote terminal application, allowing one host to connect to and run a sessions on another host. Uses TCP for acknowledged communications.
• FTP supports file transport between dissimilar systems. Telnet is used for initial user authentication. PUT and GET are two common file management commands useable with FTP.
• SMTP provides a mechanism for the exchange of mail information between systems.
• SNMP (Simple Network management Protocol) is a TCP/IP based management protocol. Uses UDP to send control and management information between TCP/IP hosts. Gives you the capabilities of remote device control and parameter management.
• DNS. Through DNS, a common naming convention is provided throughout the Internet. Requires a static name-to-IP address mapping.
  A zone file contains the resource records for the part of the domain for which the zone is responsible. Some of the resource records are:
  
  • SOA (Start Of Authority Record): The first record in any zone file is the SOA record. The SOA file contains some general parameters such as contact e-mail of the person responsible for this zone file, the host on which zone file is maintained etc.
    
  • The NS Record (Name Server Record): NS Record contains the name servers for this domain. This will enable other name servers to look up names in your domain.
    
  • MX Record (Mail Exchange Record): MX record tells us which host processes mail for this domain.
    
  • Host Record (A Record): A host record is used to statically associate hosts names to IP addresses within a zone. The syntax for this is
    <hostname> IN A <ip address of the host>
    ex:
    NameServer1 IN A 196.52.34.143
    Here 'NameServer1' is the host name and 196.52.34.143 is its ip address.
    
  • CNAME Record (Canonical name): These records allow you to use more than one name to point to a single Host. Using CNAME, you can host both WWW and FTP servers on the same machine.
• NFS provides a common, transparent environment where users can share files regardless of their hardware platforms.

Dynamic Host Configuration Protol

DHCP is a way for IP addresses to be assigned and managed automatically. The DHCP server can be configured to provide the DHCP client with other information, as default gateway address and WINS server address. The DHCP server will have a set pool of addresses, known as its address scope.

• The client broadcasts a request for an IP address.
• The DHCP server responds with an IP address offer.
• The client accepts the offer and configures itself with the IP address and subnet mask.

The client is given the address for a specified period of time, known as the lease period. Along with it's leasetime, a DHCP client receives two additional times; T1 (50% of the lease time) and T2 (87,5% of the lease time.). The client will attempt to renew the address before the lease period runs out (T1) and, if unable, will attempt to bid for a new address after the lease expires (T2).

Some systems cannot be DHCP clients, this includes systems that must have a set IP address, such as DHCP servers, WINS servers and IP gateways (routers). These addresses must be manually assigned and excluded form the scope.

Browser issues

A browser is the user's window on the Internet. It is a software application that can locate and display Web pages that include text and graphics. Browser include Microsoft Internet Explorer and Netscape Navigator.

The relationship between a file type and its associated application must be configured on a user's computer. This file type association is how the operating system knows which application should handle a particular file type. File type association are defined in the MIME Map Dialog of IIS and similarly in other Web server applications.

Cookies

When you visit a web site, it may save a special text file on your hard-disc containing information specific to you. This file is called a cookie. When you revisit that site, it will remember you by reading back the information stored in a cookie.

Information put into cookies is collected through site registration, online surveys, site customization by the user, and information collected when a customer places an order.

There are two types of cookies:

• Sessions cookie
  Are put on your computer and last only till you log out. Has no expiration date. This may be useful for online shopping, where the cookie saves information about things in your shopping cart and then discards it when you log out without purchasing.
• Persistent cookie
  Will last for a certain amount of time, depending on the expiration date placed on that cookie.
  

Cookies are used for:

• Online shopping, keeping track of your items in the shopping cart.
• Personalization, e.g. remembering and greeting you by name.
• Web site tracking.

You can set your browser to:

• automatically accept all cookies (default)
• block all cookies
• warn you before accepting/denying a cookie

IE stores cookies as separate text-files stored in a folder called Cookies.
NS stores cookies in one text-file called cookies.txt

A web site can set multiple cookies. The maximum number of cookies is 20 per domain.

The maximum size of cookies is 4KB in size. The cookies larger than 4KB will still be set, but the file will be trimmed. Usually the cookies directory is limited to 1.2MB of the client's hard drive. When the limit on number of cookies is reached, the least recently used cookie is deleted.

Only executable files can spread viruses. Cookies are contained in text-files, storing data and not programs, so they are not able to transmit a virus or damage your system. The concern about cookies is more about privacy.

Chapter 1 Chapter 3