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Topic: Networking Settings And Communication |
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dns
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| Networking Settings And Communication |
Here comes the basic networking: Intranet + Internet
Internet
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HostNo4(Gateway)
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HostNo1 HostNo2 HostNo3(NDS Server) HostNox
192.168.0.1 HostNo1
192.168.0.2 HostNo2
192.168.0.3 HostNo3 DNS Server
192.168.0.4 HostNo4 Gateway
The question is how does computer HostNo1 find HostNo2 and talk to it?
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dns
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| How does computer know each other within an Intranet? |
To form an Intranet network, computers are connected by physical cable and network cards. As each network card bears a globally unique identification number, computers can identify the others and be distinguished from each other. This unique card identification number is also referred to as physical address which usually takes the form like 00:4a:2e:43:57:04.
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dns
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| The First Layer Abstraction -- IP Address |
The network physical address is usually encapsulated by a logic address, i.e. IP address, for the purpose of:
independence -- an abstract address based networks can hook any machines.
flexibility -- an abstract address based network architecture can be easily managed and maintained.
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| ARP -- Address Resolution Protocol |
The mapping between logic IP addresses and physical network addresses is resolved by Address Resolution Protocol (ARP).
Here is an example how 'HostNo1' finds the destination 'HostNo2' by resolving its IP address 192.168.0.2:
c:\ ping 192.168.0.2
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-> 192.168.0.1 Broadcast ARP* Who has 192.168.0.2? Tell 192.168.0.1
<- 192.168.0.1 192.168.0.2 ARP 192.168.0.2 is at 00:1a:2d:4f:50:69
-> 192.168.0.1 192.168.0.2 ICMP* Echo request
<- 192.168.0.1 192.168.0.2 ICMP Echo reply
* ICMP -- Internet Control Message Protocol
* ARP -- Address Resolution Protocol
In order to know where is 192.168.0.2, the host 'HostNo1' broadcast within the Intranet with the ARP by saying "Who has 192.168.0.2? Tell 192.168.0.1"
Once 'HostNo2' gets this message, it knows the message is for him to resolve and replies by telling 'HostNo1' "192.168.0.2 is at 00:1a:2d:4f:50:69"
Once 'HostNo1' gets the destination's physical address, it can transmit any data packets though cable connection to 'HostNo2'.
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| The Second Layer Abstraction -- NetBIOS Name And Domain Name |
The logic IP address is usually further encapsulated by a NetBIOS name or domain name, for the purpose of:
readability -- an abstract name based networks is more readable and memorized.
portability -- an abstract name based application can run on any machine with different IP address.
scaleability -- an abstract name based network architecture can hook more than one computers (IPs) to serve a single well-known domain name by diversifying the network traffic.
For example, few people know what '66.94.230.41' is because it is hard for human beings to memorize such a long meaningless digits. But most people know what 'www.yahoo.com' is.
In terms of portability, the domain 'www.yahoo.com' can run on any IP address like '66.94.230.41' or '66.94.234.13'
For scaleability, 'www.yahoo.com' can hook a cluster of machines running on different geographical locations to tackle local traffic for fast turn out. |
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| WINS -- Windows Internet Naming Service |
WINS is short for Windows Internet Naming Service, a system that determines the IP address associated with a particular network computer assigned with a NetBIOS name, which is a 16-byte address that is used to identify a NetBIOS resource on the local area network (LAN). This is called NetBIOS name resolution. WINS supports network client and server computers running Windows and can provide name resolution for other computers with special arrangements. Determining the IP address for a computer is a complex process when DHCP servers assign IP addresses dynamically. For example, it is possible for DHCP to assign a different IP address to a client each time the machine logs on to the network.
WINS uses a distributed database that is automatically updated with the names of computers currently available and the IP address assigned to each one.
WINS server is called via NetBIOS Name Service (NBNS) if match is not found in local cache.
Here is an example as to how a computer NetBIOS name is resolved. The traffic details of ping are listed below:
c:\ ping HostNo2
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-> 192.168.0.1 192.168.0.255 NBNS* Name query NB HostNo2<00>
192.168.0.2 Broadcast ARP Who has 192.168.0.1? Tell 192.168.0.2
-> 192.168.0.1 192.168.0.2 ARP 192.168.0.1 is at 00:01:02:4f:5b:6e
<- 192.168.0.1 192.168.0.2 NBNS Name query response NB 192.168.0.2
-> 192.168.0.1 192.168.0.2 ICMP Echo request
<- 192.168.0.1 192.168.0.2 ICMP Echo reply
* NBNS -- NetBIOS Name Service, using port 137
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posted on: 07/06/2006 07:38:34 PM
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