1. What is network and internet?
Network is an aggregation of computers interlinking with cable, line, or
wireless communication. With network, you can share or change network
data and information with other network users online.
Generally, we
separate network as LAN (Local Area Network) and WAN (Wide Area Network)
according to the area size of computer's linking. The network in a
house, a building or a campus is so called LAN, and the network spanning
regions and countries is called WAN. Internet is the biggest typical WAN
which originated from ARPANET (A Program by Advanced Research Project
Agency of US Department of Defense) in 1969. In 1986, NSF( US National
Science Foundation) created NSFNET with TCP/IP sponsored by the
government and opened it to public as Internet in 1989.
With the
commercialization and popularization of network in global scope,
Internet has been becoming a name of information modernizing. We can say
Internet is a data library covering nearly everything, or Internet is a
hinge central of the whole world through which you can gain
international news, chat with friends, write or read emails, shop
online, view films, listen concert and do many other things.
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2. What is Ethernet?
Ethernet was originally developed by XEROX Corporation. Due to the using
of DEC, INTEL and XEROX together, Ethernet was configured in 1980 and
adapted by IEEE as 802.3 standard afterwards.
The basic feature of Ethernet is to adopt a kind of shared access plan
called CSMA/CD (Carrier Sense Multiple Access/Collision Detection), that
is, multi workstations connect on a central line and all workstations
send monitoring signals ceaselessly to the central line. However, only
one workstation can transmit signals on the line at one time and the
others must wait for starting their own transmission until that
workstation finishes.
- Ethernet and LAN
Only a kind of LAN, Ethernet is in parallel with Token-Ring and FDDI and
involved in LAN system.
Nowadays, 90% network is Ethernet for it is the main technique applied
in LAN at present so that Ethernet almost has been another name of LAN.
- Types of Ethernet
- Classified by speed, Ethernet has 10Mbps Ethernet, 10/100Mbps
Ethernet, 1000Mbps Ethernet and 10Gbps Ethernet;
- Classified by the usage type of wideband, Ethernet has shared
Ethernet and switched Ethernet two kinds.
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3. What is network arrangement?
Network is a combination of communication and computer resources which
normally are kept in network equipments called as nodes. Network
arrangement is to fulfill the tasks we need by using softwares on these
nodes, commonly including four aspects:
- System arrangement: Supervising computer and its groupwares;
- Protocol arrangement: Arrangement of network protocols used to
communicate and transfer information;
- Application arrangement: Arrangement of softwares or programs applied
by network users;
- Service arrangement: Arrangement of other services supplied by
network service providers.
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4. What is network security?
Network security means that a network system, including hardware,
software and all the data saved in this system, can run normally,
continually and stably. In general, network security possesses four
features:
- Privacy: Information can not be detected by any other person except
sender and receiver;
- Integrality: Data are protected from being modified damaged randomly;
- Identity: Users must have corresponding identification before using
network resources;
- Authorization: System can accredit a certain user and judge the
sufficiency of authority;
- Irrefutability: Based on authority as certification of certain
activity.
Although the global economy is becoming more and more reliant on
network, the security of network is still very worrying for that many
means may attack network and cause it disable. The most general menaces
to network security are:
- Hacker: Most hackers are IT geniuses who can find the leaks in system
and enter your computer to rip off or damage your data;
- Erotic website: There are millions websites global wide containing
erotic contents and produce a lot of junk mails, which not only are very
harmful to the minors but also occupy large quality of network
resources:
- Virus: Viruses may destroy computer system and damage your important
data.
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5. What is system's vulnerability?
Vulnerability is originated from system's security Bugs, which may exist
in software programs and CMOS chips as well, and often utilized by
hackers up to no good as the leak to disable personal computer and
network.
System's vulnerability mainly represents as follows:
- Software's Bug
The Bugs in Server's daemon threads, applications, operation systems and
protocol stacks will arose system's vulnerability and may utilized by
attackers. Theses Bugs reflect that the settlement to exceptional input
did not be considered when programmed, including:
- Buffer's overflow;
- Combination of special characters;
- Competition conditions.
- Inappropriate configure of system
- Default configure;
- Misconduct by administrators;
- Back door of system;
- Trust connection
- Vulnerable password
Most of passwords consist of names, simple numbers, or as same as
accounts. Attackers can gain password easily by guessing or reckoning.
- Information leak
The main means used by attackers is wire tapping. If the network
interface card on LAN is set as miscellaneous mode and the server is
installed with a sniffer, attackers can view all packets on network and
obtain remote user's account and password.
- Design limitation
- Protocol limitation
The most typical is TCP/IP.
- Operation system limitation
To view network vulnerabilities list, click here.
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6. What are network protocols?
Computers need to abide by certain regulations together to communicate
normally via network (involving internet), these regulations are so
called network protocols. Network protocols are usually sorted into
several layers and each layer has its own functions.
A computer must
comply with network protocols in order to communicate with others, and
only those on a same protocol layer may contact each other.
TCP/IP and IPX/SPX are two most popular protocols, the prior is used widely on
internet, and the latter is used normally on intranet.
Want to know more information about network protocols? Click here.
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7. What are network packets?
Packet is data unit of TCP/IP communication transferring, which operates
on the second layer (network layer) and the third layer (transport
layer) of OSI.
The framework of a packet is very complicated, but
primarily, it is composed of destination IP, source IP, data, etc.
Destination IP is the IP address of receiver where this packet will
reach; source IP is the IP address of sender where the packet is from;
and data is the content of this packet. Only those computers installed
TCP/IP protocols can communicate with each other owing to such framework
of packet, in fact, when we communicate via network which bases on
TCP/IP, what transferred through network are packets. To keep network
secure, network administrators need to know what packets are active on
network by analyzing packets and find out the problems. In a word,
comprehending and parsing packets are essential to network security.
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8. What is network attack?
Initially network attack indicated those illegal and unauthorized visits
to computers, called: Cracking and hacking pointed to the applications
of computer techniques by professionals who can operate computers
skillfully.
But nowadays, hacking has changed its originated meaning
into attacking, and becomes synonymous as damaging network, burgling
network information and so on network lawbreaking activities. Most
attacks are prankish without a lot of damages for the limited network
knowledge and operation skills of attackers. But some attacks to
computer are fatal if the attacker can find out leaks of system or
software and utilize the leaks to attack.
To prevent network attack, the first thing to do is to detect and
analyze the IP address of attacker. Capsa can help you to do that.
Download Capsa to try, or go for more details.
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9. What is network monitoring?
Do you know why network monitoring is so important in internet
management? According to a report, 30%-40% of employees' network
activities are irrelevant to their work, 37% employees state that they
often surf online during working time, and 70% visits to erotic websites
happen at working time. These are also the reasons why there are 80%
American and European corporations have taken steps to monitor the
internet activities of employees.
Network monitoring, in nature, is to read and parse the contents of
packets transferred on network. The operation principal of network
transmission is that a host sends packets to another host, each packet
involving data and frame which covers the information of packet like
source and destination. The data of a packet may be email, web page,
registration information, password, e-business records, and other
information of network transactions.
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10. What is network analyzer?
Network analyzer is also called as protocol analyzer, which is necessary
for users who want to know how the network operates. Basically, an
advanced network analyzer may possess following functions:
- Captures all packets or appointed packets by presetting filters;
- Decodes packets and display data in the packets;
- Parses the modes of communication protocols;
- Shows other information of captured packets like IP address of source
and destination, name of host or server, traffic, etc.
A good network analyzer can be user's right hand as it provides many
data for troubleshooting; it is also an application tool to monitor
network activities.
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11. What is IP address?
IP address is an import concept on network. An IP address is a unique
32bit address distributed to each host connecting Internet global wide.
IP address is showed with four decimal numbers separated by dots; each
number is homologous to eight binary bits, such as: 128. 52. 3. 2.
Internet NIC (Internet Network Information Center) is in general charge
of laying out and managing global IP addresses and the particular
distribution of IP addresses in United States and other districts is
presided over together by Internet NIC, APNIC, RIPE. Generally each
country needs to found an institute which will take charge of applying
IP addresses to relevant international organizations before distributing
to every client.
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12. What is MAC?
MAC is the physical address of network interface card used to identify
it from other network interface cards. In general, the MAC address of
every network interface card is unique which mostly is comprised of 6
bytes 48 bits.
To know your own MAC address, you can run ¡°command¡± program in start
menu and perform ¡°WinIPcfg¡± command in opened DOS window under Win9x or
run ¡°cmd¡± program in start menu and perform ¡°IPconfig-all¡± command in
opened DOS window under Windows2000 and XP.
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13.What is the difference between IP and MAC address?
IP address is used by Internet protocols while MAC address is used by
Ethernet protocols, and there is no necessary relevance between each
other.
MAC address is 48 bits, which attached with Ethernet NIC (network
interface card). Every Ethernet NIC producer must apply a series of MAC
addresses for IEEEE organization and program it in EEPROM on NIC when
producing NIC. The MAC address of any two NIC should be different,
whatever producer it is from. MAC address is in every Ethernet packet as
a part of Ethernet header and packets can be exchanged and transferred
by Ethernet repeater according as the MAC source and destination address
in Ethernet packet header.
Every Internet packet must have IP address which is distributed by
Internet service providers (ISP). IP address usually works on WAN while
MAC address on LAN. Most interlinks of LAN are achieved by current
public web or leased line which require conversion of protocols, and
although IP information can be transmitted on Ethernet, it still has to
be dealt with by upper layer of network as ordinary data for it is only
a part of packet header and cannot be viewed by Ethernet repeater.
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14. What is Port?
Port in network technique has several meanings. Port of Hub, Switch, and
router is the meeting point connecting other network equipments, such as
RJ-45 port, Serial port. But generally, port denotes specially the port
in TCP/IP protocol which is its logical sense while not physical sense.
Port is the approach via which a computer communicates with others. We
know a host with IP address can offer many kinds of services, like Web
service, FTP service, SMTP service, etc, a host distinguishes different
network services through IP address and port number. According to
protocol type, port can be separated as two kinds: TCP port and UDP
port, both are independent and have no conflict with each other. Click here to search a port.
The port numbers are divided into three ranges: Well Known Ports, Registered Ports, and Dynamic and/or Private Ports.
Well Known Ports:
The Well Known Ports can only be used by system (or root) processes or by programs xecuted by privileged users on most systems .
Ports are used in the TCP [RFC793] to name the ends of logical connections which carry long term conversations. For the purpose of providing services to unknown callers, a service contact port is defined. This list specifies the port used by the server process as its contact port. The contact port is sometimes called the "well-known port".
Registered Ports:
The Registered Ports can be used by ordinary user processes or programs executed by ordinary users on most systems.
Ports are used in the TCP [RFC793] to name the ends of logical connections which carry long term conversations. For the purpose of providing services to unknown callers, a service contact port is defined. This list specifies the port used by the server process as its contact port.
Dynamic and/or Private Ports
The Dynamic and/or Private Ports are those from 49152 through 65535.
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15. What is Frame?
Frame is the minimal unit in network transmission which is composed of
binary data. Frame scale of Ethernet floats between 63 bytes at least to
1518 bytes at most, and in practice it is MTU (most transfer unit) of
equipment to decide Frame size automatically. Frame is produced when
computer transmitting data, say more accurately, is produced by network
interface card (NIC) installed in computer. Frame is nothing to Hub
since it is significative only to those equipments which can recognize
it.
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16. What is network interface card?
NIC (network interface card) is the hardware equipment connecting
computer with network physically. As the direct connection between
computer and communication medium on LAN, NIC has different types
according to network techniques, for instance, ATM NIC, Token-Ring NIC,
Ethernet NIC and so on. Approximately 180% LAN, as statistics, adopts
Ethernet technique currently.
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17.What are network relays?
Computer network consists of many different kinds of network that
interlink each others, such interlinkage requires to be achieved with
some medium devices which are called as ¡°relay system¡± by ISO terms:
- Physical layer (L1) relay: Repeater;
- Data link layer (L2) relay Bridge;
- Network layer (L3) relay: Router;
- Brouter: admixture of Bridge and Router, possessing the functions
both of Bridge and Router;
- Relay above network layer: Gateway.
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18. What is Hub?
Hub is a connection device connecting multi computers or other
equipments in network. As the minimal unit of concentrated management in
network, many kinds of network need to rely on Hubs to connect various
devices and distribute data to each segment. Basically, Hub is a shared
device which main function is to magnify and transfer signals by
distributing the signals received from a port to all ports. Some Hubs
magnify weak signals before distributing while some others arrange
signals to offer synchronous data communication for all ports.
There are multi kinds of Hubs, each having certain functions and
providing different level services. Rife division is on the basis of
working features:
- Passive Hub
Only connects multi segments of network medium and allows signals pass
through without any disposal.
- Active Hub
Besides possessing all the functions of passive Hub, active Hub can
monitor data and redress damaged grouping before Ethernet performs
storage and repeat function.
- Intelligent Hub
Possesses the features of active Hub, furthermore, intelligent Hub also
provide central management function which makes it easily to find out,
diagnose and remedy those problems occur on the devices connected to it.
Another outstanding feature is that it can transfer data with various
speeds for different devices, supporting Ethernet, Token-Ring and FDDI.
- Switching Hub
A kind of intelligent Hub and holds the ability of switching routes and
segmenting network in addition to basic functions of intelligent Hub.
Sometimes is classified as primary Switch.
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19. What is Switch?
Switch is a kind of network device which is based upon MAC
identification and can fulfill the task of transferring packets with
encapsulation. A Switch may learn MAC address and save it to inner
address list, transferring data frame from source address to destination
address through the switching path created temporarily between sender
and receiver.
Switch and Hub both follow IEEE802.3 or IEEE802.3u standard and use CSMA/CD
technique to access network.
Switch differs from Hub mainly on two aspects:
- Hub is shared while Switch is exclusive;
- The security of Hub is lower than Switch's for it transfers packet to
all ports while Switch can transfer packet to corresponding port via
analyzing packet header;
- Hub deals with one packet at a time while Switch can transact large
quantity of data synchronously.
As viewed from transfer medium and transfer speed, Switch can de
separated as Ethernet Switch, Gigabit Ethernet Switch, FDDI Switch, ATM
Switch and Token-Ring Switch. But classified with the most common
method, Switch has three types: Desktop Switch, Workgroup Switch and
Campus Switch.
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20. What is Router?
Router is a kind of network device used to connect multi networks with
different protocols and architecture. The basic function of Router is
transferring packets to proper network, including:
- Determining route and transmitting IP packets;
- Isolating subnets to control broadcast storm;
- Maintaining routing lists and exchanging routing information with
other Routers;
- Rectifying errors of IP packets and simple congestion control;
- Filtering IP packets.
On backbone web, Router is focused on selecting routes. It must know the
accesses to all lower networks so that it needs to maintain an enormous
routing list and react to the changes of connecting status as quickly as
possible. A fault of Router may lead to serious troubles in data
transmission.
On area web, the main function of Router is network selection and routes
selection, namely to connect each skeleton network unit on underlayers
and to take charge of transmitting data among lower layers.
The two major types of Router are:
- Static Router
Requires administrators of setting up and configuring routing table to
specify each route manually;
- Dynamic Router
Automatically find out routes and set up the minimal configuration.
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21.What is Bridge?
Bridge works on data link layer connecting two LANs and transmitting
frames by MAC addresses and can be viewed as a lower router. Bridge
differs from Router in following aspects:
- Bridge doesn't know the information of middle and upper protocols
involved in the frames it transmits, such a feature enables it to settle
protocols like IP, IPX and so on with same means at the same time. It
also possesses the function to segment networks without route protocols
(such as NetBEUI). Whereas Router deals with the data on network layer
so that it may interlink different data link layers (Token-Ring segment
and Ethernet segment);
- Router transmits data by IP address and more easily to be controlled
than Bridge;
- Bridge is applicable to simple or small scale network commonly.
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