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Chapter 4 - Networking concepts

Describe Internet infrastructure and the relationship between its entities.
Identify Internet connectivity problems.
Use diagnostic tools to solve Internet connectivity problems.
Describe DNS and Internet domain names.
Describe public, private and operational aspects of TCP/IP.
Describe various remote access protocols.
Describe e-mail and mail services protocols.
Describe hardware connection devices and their purposes.
Describe Internet link and bandwidth technologies
Describe the functionality and features of various Internet services.

Internet Infrastructure

The Internet backbone is the national and international network of large access points that link the Internet worldwide. The backbone consists of large switches linked together by high-bandwidth, high-speed digital lines. These large switching points, called Network Access Points (NAPs) are a collection point and a Grand Central Station for Internet Service providers (ISPs) to access the Internet, they provide Internet access to ISPs. It is the ISPs that further distribute Internet access to end users. ISPs connect to the NAPs using primarily OC-12, OC3 ATM and DS3 ATM.

Internet servers

A single physical server may provide one or more of the services listed:

HTTP (Web) servers
- Web servers are designed to use HTTP to move hypertext files across the Internet. The engine of the Web server is called an HTTP daemon. The daemon waits for HTTP requests from clients and handles requests when they arrive.
  The establishment of an HTTP connection by the client to a server usually uses the well-known port 80, the default port used for HTTP.
  HTTP 1.1 supports persistent connection. This means that once a browser connects to a Web server, it can receive multiple files through the same connection, This improves performance with up to 20%.
  Browsers supporting HTTP 1.1 will compress HTML files for transport across the Internet. This also provides a substantial savings in the amount of data that must be transmitted.
  HTTP 1.1 provides the ability to have multiple domain names share the same Internet address. This allows Web servers to host a number of Web sites. A Web site that does not have its own IP address is called a virtual server.
FTP servers
- FTP servers listens on the well-known port number 21 for control connection requests. FTP servers store and retrieve files that usually are organized by subjects. FTP servers are designed for quick, reliable file uploads and downloads between the server and an FTP client.
  You can FTP from the Dos command line or through a FTP-program. Vital commands are open (to establish contact), get (to download files) and put (to upload files).
Mail servers
- The primary function of a mail server is to receive and transmit e-mail from multiple users using e-mail clients. Popular e-mail servers include Microsoft's Exchange Server, Novell's Group Wise, ccMail and UNIX's sendmail.
Telnet servers
- Telnet is a terminal emulation program. Once you are logged on to a network, you can use a terminal emulation program, e.g. PC Anywhere, to control a remote server as though you were a user logged on locally.
List servers
- List servers are used to maintain subscription e-mail mailing lists and to distribute information to the e-mail addresses on the mailing list. E.g. newsletters. Push-method.
  Lists servers content may also come from subscribers. Many list-servers allow subscribers to send e-mail to a specified e-mail address for distribution to the whole group.
News servers
- News servers support the distribution of news from users. The news is indexed by subject, and a string of posted articles (posts) collectively are called a newsgroup.
  News servers distribute news content to subscribers. It is a function similar to that of list servers except that news servers operate on the pull model. No content is distributed unless the subscriber connects to the news server. The content is downloaded to the user's Network News Transport Protocol (NNTP) viewer. The NNTP reader accesses the news server at the well-known port 119.
LDAP (Directory) servers
- Directory servers hold indexed databases of categorized information that users can query. Two popular uses of directory servers are indexing Web sites by subject and indexing e-mail addresses and other personal information into white pages.
  On the Wen, some directory servers index Web sites by keywords, others like Yahoo! use a hierarchical tree of topics and subtopics.
  The other major use of a directory server is to develop indexes of directory information, such as e-mail addresses and public keys using Lightweight Directory Access Protocol (LDAP). LDAP is a simplified version of the X.500 protocol.
Mirrored servers
- Mirrored servers are servers that maintain copies of the same files as another server and are typically used to backup primary servers. If the primary server fails, the mirrored server continues to operate without any downtime. They can also be used to spread the load to more than one site.
Certificate servers
- Certificate servers are designed to issue certificates (IDs).You must request a certificate for your organization through a Certificate Authority (CA)
  Secure Sockets Layer (SSL) uses a public and private key encryption system that also incorporates the use of digital certificates. The most widely used standard for defining digital certificates is X.509.
E-commerce servers
Proxy servers
- Proxy servers are designed to sit between a client computer, such as a browser, and a Web server. A proxy server intercepts all requests to the Web server to see if it can fulfill the request itself, but otherwise forwards the request o the Web server. The proxy server caches Web pages from an Internet Web server and acts as an intermediary or buffer between a Web client and a Web server.
  Proxy servers are also gateways that allow direct Internet access from behind a firewall. Proxy servers open a socket on the server and allow communication to the Internet via that socket. Proxy servers improve performance, filter requests and provides security.
  An IP proxy masks the IP address of internal hosts and represents itself instead.

Mail systems

Simple Mail Transfer Protocol (SMTP) is one of the most widely used protocols on the Internet. It was designed to handle the transfer of messages from one host to another. SMTP is not a mail system, only mail transfer protocol. It provides a mechanism for transferring messages between hosts, for queuing messages until a message can be forwarded (store and forward) and for notifying the sender when the mail cannot be delivered. By default SMTP uses port 25.

Web Systems

TCP/IP
- is the protocol you use when connecting your network to the Internet.
DNS
- is a client/server protocol that translates TCP/IP host names into numeric IP addresses. DNS maintains a set of tables that map host names to IP addresses.
Name resolution and WINS (Windows Internet Name Service)
- A critical issue in networking is the resolution of host names. Microsoft's implementation of TCP/IP supports the following:
  - HOSTS file
    Uses a text file to associate a host name with an IP address. Does not support NetBIOS-based applications.
  - DNS
    Supports fully qualified host names, including IP domain, subdomain and host name.
  - NetBIOS broadcast
    Resolves NetBIOS names and IP addresses through broadcasts.
  - LMHOSTS file
    Similar to HOSTS file, it maintains a textfile located on the local machine or accessed through network shares. Supports NetBIOS names.
  - WINS
    An automated NetBIOS name resolution ,method. WINS clients automatically register themselves with the WINS server, which can be queried for name resolution. NetBIOS names can also be manually entered into the database.
Network News Transport Protocol (NNTP)
- NNTP services allows your server to act as a news server by providing newsgroup services to NNTP clients. Default port is 119.
- 128-bit encryption
- IP filtering
  - Granting or denying access to specific IP addresses by specifying a single client IP address, a group of addresses using a subnet mask. Or a domain name.
File transfer systems
- Default port for FTP is 21.
  Administrator can assign:
  - usernames and passwords
  - a Welcome message
  - an Exit message
  - a Maximum connections message (displays when the site has reached the maximum number of user connections allowed)
  - access permissions for the FTP root directory (read/write)

Basic definitions in advanced Internet addressing

Packet
- Information being sent across the network is referred to as packets. A message will often contain several packets that must be delivered, in order, with the data intact.
Protocol
- A set of rules defining how two processes communicate.
Host
- Also referred to as an end node. A device configured as part of the network. The destination for an IP packet.
Address
- Each node must have a unique address to communicate via TCP/IP. The address must follow the IP address format.
Names
- Each host will also have a unique name. A common method for managing names is DNS. DNS servers map up IP addresses to DNS names.
Routers
- Routers connect networks together using the network portion of the IP address to identify appropriate subnetwork. A router reads a packet from one network, determines whether that packet is destined for another network, and forwards the packet appropriately.

IP addressing

IP4, the current version of IP, uses a 32-bit address scheme that allows for 4.294.967.296 or 232 IP addresses.
IP addresses are 32 bits long
IP addresses are are divided into four octets.
Each octet contains 8 bits with values ranging from 0-256
A bit is represented by a zero or one.

Position	8	7	6	5	4	3	2	1
Power of 2	27	26	25	24	23	22	21	20
Decimal value	128	64	32	16	8	4	2	1
Example	1	1	0	0	0	0	0	1
Equals	128	64	0	0	0	0	0	1
Total	128 + 64 + 1 = 193

So an IP address that numerically reads: 196.250.28.3 will binary read:
11000100.11111010.00011100.00000011

Address classes

Five address classes (A through E) are supported. Only Classes A, B and C are assigned to the general community. Class D is reserved for multicasting and Class E addresses are reserved for experimental purposes. A value of 127 in the first octet is reserved for loopback testing.

Class	Opening bits	Default subnet mask	Network range	# of networks	# of hosts per network
A	0	255.0.0.0	1-126	126	16,777,214
B	10	255.255.0.0	128.0 - 191.255	16,384	65,534
C	110	255.255.255.0	192.0.0 - 223.255.255	2,097,152	254
D	1110	n/a	224-239	n/a	n/a

All class A addresses are already allocated, and Class B addresses are difficult to obtain. New connections to the Internet are assigned Class C addresses.

In a Class A network, the first octet defines the network portion of the address. The last three octets are used for subnet masking and host addresses.
In the first octet, the first bit must be set to zero. Only the remaining seven are used for addressing and can be set to either zero or one. This defines 128 Class A networks with network addresses ranging from 0 to 127. Out of these only 126 are useable. Addresses 0 and 127 are reserved.
A default subnet mask of 255.0.0.0 is assigned for a Class A network. This means that you cannot change the value of any number positioned in the first octet, the assigned network address.
Class A networks support up to 16.777.214 (224 -2) hosts. You cannot use 0.0.0 or 255.255.255 as the host portion of the address. A host address of all 0s means this network, and a host address of all 1s means broadcast to all nodes.

In a Class B network, the two first octet defines the network portion of the address. The last two octets are used for subnet masking and host addresses.
In the first octet, the first bit must be set to one, and the second to zero. The remaining six, plus all eight in the next octet are used for addressing and can be set to either zero or one. This defines 16,384 Class B networks with network addresses ranging from 128.0 to 191.255.
A default subnet mask of 255.255.0.0 is assigned for a Class B network. This means that you cannot change the value of any number positioned in the first two octets, the assigned network address.
Class B networks support up to 65,534(216 -2) hosts. You cannot use 0.0 or 255.255 as the host portion of the address. A host address of all 0s means this network, and a host address of all 1s means broadcast to all nodes.

In a Class C network, the three first octet defines the network portion of the address. The last octet is used for subnet masking and host addresses.
In the first octet, the two first bits must be set to one, and the third to zero. The remaining five plus the two next octets are used for addressing and can be set to either zero or one. This defines 2,097,152 Class C networks with network addresses ranging from 192.0.0 to 223.255.255.0.
A default subnet mask of 255.255.255.0 is assigned for a Class B network. This means that you cannot change the value of any number positioned in the first two octets, the assigned network address.
Class C networks support up to 254(28 -2) hosts. You cannot use 0 or 255 as the host portion of the address. A host address of all 0s means this network, and a host address of all 1s means broadcast to all nodes.

A private Internet is one that will not be connecting directly to the Internet. The term intranet is commonly used to refer to networks of this type. The Internet Assigned Numbers Authority (IANA) has set aside the following three sets of addresses for use on intranets:

10.0.0.0 to 10.255.255.255
172.16.0.0 to 172.31.255.255
192.168.0.0 to 192.168.255.255

Internet hardware

Internet hardware and platforms
- The hardware physically tasked with handling data on the network: servers, workstations, NICs, cabling, hubs, routers...
- A platform refers to a given combination of hardware and software in a given environment that all works together, e.g. IBM PCs or compatible running MS/DOS, Windows 3.1 or Windows 95.
Network adapter cards
- Also referred to as a Network Interface Card (NIC)
- provides a communication channel between your computer's motherboard and the network.
- The Media Access Control (MAC) address is your NICs unique hardware identifier, and are hexadecimal numbers that are assigned to each NIC during the manufacturing process.
Bridges
- Provide a way of segmenting network traffic and connecting different types of network (different LAN types).
- Operates at the Data Link Layer, or more precisely, on the MAC sublayer.
- Can filter traffic based on addresses.
- Cleans and amplifies signals allowing for expanded networks.
- Modern bridges are usually referred to as learning (transparent) bridges because the are capable of automatically identifying devices on the segments they connect.
- Bridge filtering consists of looking for patterns within the frame to selectively control frames that will be forwarded.
- Layer 2 Switch (data switch) is generally a more modern term for multiport bridge.
Routers
- Allow you to build an internetwork computing environment and are a key element in wide area networking.
- Operate on the Network Layer.
- When a router receives a packet, it will generally forward it to the appropriate network based on a table maintained in the router. The tables may be static or dynamic.
- The router provides a port of entry that can control entrance and exit traffic to and from a subnet.
- Routers should be given preference over bridges when designing and configuring WANs.
Brouters
- operate on both the Network Layer for routable protocols and at the Data Link Layer for nonroutable protocols.
- A combined bridge and router.
Hubs
- When wiring Ethernet in a star topology, it is necessary to use a device that will take the signal transmitted from one computer and propagate it to all computers on the network.
  - Passive hubs
    Takes incoming electric signals one one port and passes them down the cable on its other ports. In this way, all nodes see the signal as if they were all connected on a physical bus topology.
  - Active hubs
    Repair weak signals
  - Switching hubs
    Builds on the features of an active hub. A switching hub takes an incoming packet of data and actually looks inside at the destination hardware address. Then instead of rebroadcasting this packet on all ports, the hub only sends the packet out the port connected to the destination machine.
  - Intelligent hubs
    May have advanced features such as built-in routing or bridging functions
Firewalls
- A firewall is a mechanism for controlling access between networks. Provides an extra layer of security to protect private organizational systems from external intruders and can be hardware based or software based.
  Typically, firewalls are implemented within the router that connects the private network with the public network.
  It is also possible for firewalls to filter and deny access to Web sites that are considered inappropriate.
  - Packet filtering
    is the technique of examining each datagram as it passes through a router. If the contents of the datagram agree with criteria defined by the security administrator and stored on the router, then the datagram is passed on to its destination.
  - Bastion hosts
    are heavily fortified servers on the network that all external traffic must pass through. All services except those absolutely essential to running the system is eliminated. In this way, even if an intruder were to break into the system, damage would be limited.
All-in-one solutions
- Or Internet-in-a-box are software packages that provide Internet access to a LAN without loading additional services on the network servers. Services such as a-mail, ftp, gopher and Telnet are parts of the package.

Remote access and diagnostics

Ping
- The Packet Internet Groper is used to test TCP/IP connectivity by transmitting Internet Control Message Protocol (ICMP) packets to a TCP/IP host. The host should then echo the packets back to the original IP address. Tests for presence of other systems.
  Ping yourself with the loopback address 127.0.0.1 to determine if you have a working TCP/IP stack.
IPconfig
- The Internet Protocol Configuration utility is used to view TCP/IP configuration information from a command prompt, including IP address, subnet mask, and default gateway.
Tracert
- Is used to check the availability of routes to a given destination network. It also provides timing information that can be used to identify bottlenecks in an internetwork or on the Internet.
  Determines the route packets take to reach the specified destination.
ARP
- Address Resolution Protocol/Reverse Address Resolution Protocol (ARP/RARP) are maintenance protocols. They are used on LANs to enable hosts to translate IP addressing to the low-level MAC addresses.
  ARP is used to request a station's MAC address when only the IP address in known.
  RARP is used when the MAC address is known but not the IP address.
Netstat
- Displays protocol statistics and current TCP/IP connections.
Route
- Displays and manipulates route information.

Remote access protocols

Serial Line Internet Protocol (SLIP)
- SLIP is a communicationsprotocol that is part of the TCP/IP suite of programs. The protocol was deviced to handle communications over fairly slow links (< 19.2 kbps). SLIP is employed over telephone lines and require minimal overhead. Disadvantages include: inability to provide packet addressing, lack of errorcorrection, lack of data compression, no flow control and no security, does not support IP addressing.
Point-to-Point Protocol (PPP)
- Provides a dial-up connection. Can be use with other protocols other than TCP/IP. Offers error correction, supports dynamic IP addressing, password logons.
Multilink PPP
- Enables two or more modems or ISDn devices to be combined as a single dial-up link that provides a bandwidth equal to the combination of modems. Increases modemspeed when using more than one modem/ISDN.
Point-to-Point Tunneling Protocol (PPTP)
- Supports all PPP features and allows for secure connections over the Internet by tunneling other protocols within TCP/IP packets. PPTP data is encrypted and encapsulated inside PPP packets. Alternative to PPTP is L2F from Cisco. Used to create VPN.
Point-to-Multipoint Protocols
- Point-to-multipointprotocols broadcast data from one sender to multiple points rather than just transmitting data to the intended recipient. On a point-to-multipoint network, a recipient's connection device is set to monitor certain bandwidth or look for certain addressing information in data packets. The connection device ignores the other bandwidths and data packets.

Internet bandwidth Linking technologies

Synchronous Optical Network and Synchronous Digital Hierarchy (SONET)
- Used for Internet backbone and for connecting large, public WAN communication systems.
  - STM 64 = 10Gbps - backbone
  - STM-16 = 2,488 Gbps - Internet backbone
  - STM-4 = 622,08 Mbps - Internet backbone
  - STM-1 = 155,52 Mbps - Large company backbone and Internet backbone
Switched Multimegabit Data Service (SMDS)
- Packet-switched technology used to connect LANs, creating MANs and WANs. Up to 155 Mbps (OC-3)
Optical fiber
- Fiber-optic cable is comprised of light-conducting glass encased in plastic fibers surrounded by a protective cladding and a durable outer sheath. Expensive.
  - OC-256 = 13,271 Gbps - backbone
  - OC-192 = 10 Gbps - backbone
  - OC-48 = 2,488 Gbps - Internet backbone
  - OC-24 = 1,244 Gbps - Internet backbone
  - OC-12 = 622,08 Mbps - Internet backbone
  - OC-3 = 155,52 Mbps - Large company backbone and Internet backbone
  - OC-1 = 51,84 Mbps - ISP to Internet, smaller Internet links
Asynchronous Transfer Mode (ATM)
- Packet switching network service that can transmit data in excess of 600Mbps. ATM is the backbone of major telecommunications companies. Provides full support for voice, video, data and fax.
Fast Ethernet and Gigabit Ethernet
- Ethernet is a technology that allows data to be transmitted between computers at 10 Mbps (10BaseT Ethernet), 100 Mbps (Fast Ethernet) or 1 Gbps (Gigabit Ethernet). Ethernet media varieties include thick coaxial, thin coaxial, twisted pair and fiber optic.
T-class carriers
- A type of high-speed leased digital telephone line used for voice and data transmission.
  - T3D = 135 Mbps - ISP to Internet
  - T3 = 44.,736 Mbps - ISP to Internet
  - T2 = 6,312 Mbps - large company connection to ISP
  - T1 = 1,544 Mbps - large company connection to ISP
E-class carriers
- E1 through E5 are the European digital transmission equivalents of the North American T-class series. Carries a higher rate than the US.
Digital Signal-X
- A collection of digital transmission transmissions based on DS0. DS0 represents a standard telephone voice channel that requires 64Kbps of bandwidth. Support from 64 Kbps to 565,148 Mbps
Fiber Distributed Data Interface (FDDI)
- OSI-compliant standard used by large, wide range, fiber-optic LANs in large companies and in some larger ISPs to support thousands of end users. 100 - 200 Mbps bandwidth.
Cable modem
- Enables data to be received at speeds up to 2,5 Mbps through the local cable TV line.
Digital Subscriber Line (DSL)
- ADSL
  Asymmetric = faster downloading than uploading. Up to 8 Mbps
- RADSL
  Speed relative to the length and quality of the local line. Otherwise same as ADSL.
- HDSL
  Same amount of download and upload speed. Can reach T1 speeds.
- SDSL
  Like HDSL, but user must be within 10,000 ft of the switching station.
- VDSL
  From 13 - 52 Mbps, within 4,500 feet.
ISDN
- A switched digital service. Speeds: 64 Kbps, 1,544 Mbps and 2,048 Mbps.
Frame relay
- Packet switching network service that provides high-speed transmission rates.
x.25
- A full-duplex, packet-switching service. Mature, well-supported, inexpensive technology that is suitable for low-maintenance global applications.

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