Destination Unknown

4박5일간의 팀합숙을 마치고 거제섬!
생각해보니까 크리스마스때 왔었구나; 두달쯤 된건가
근데 그사이에 내방이 창고화되었다 투덜투덜 쌀자루들이..
팀합숙 메시지 정리해서 올려야 하는데 피곤하니까 좀 있다가 ㅎ
바로 구정이라 아마도 내일 저녁이나 모레 아침에 전주로 출발한다

오늘 저녁에 대게를 먹었다>_<
비싼 대게~ 맛있는 대게~
근데 아직 철이 아니라 좀 작아서 아쉽긴 했다.
흐흐흐 그래도 맛있었다. 쵝오.
사실 원래 오늘 저녁에 약속있었는데 대게 먹으러 가자고 해서 취소했다. 이쁜이 미안 ㅠ_ㅠ
내일 아침에 얼라들 보고 점심때부터 보라교 아이들 보고~ 저녁에 이쁜이 보고 ㅎ
오랫만에 고향집 와서 급하게 떠나려니 바쁘네.
닷세동안 빨래도 못해서 전부 세탁기 돌리고 있다. 내일 아침까지 말라야 하는데.
오늘은 피곤하니 일찍 자고 싶으나.. 밥먹고 오징어먹고 초코렛 먹어서 일찍 자면 안 될 것 같다 ㅠ_ㅠ

초딩 일기 끝 ㅎ

에너지 용어로 말한다면
우울증은 말 그대로 무의식적으로
에너지 내지 생명력이 흩어지는 상태다.
에너지가 돈이라면, 우울증은 지갑이 열린 채로
＂내 돈을 누가 가져가서 써버리든 말든 상관없다.＂라고
말하는 것과 마찬가지다. 누가 내 돈을 얼마나 쓰든
상관하지 않는다면, 파산은 불 보듯 뻔한 일 아닌가!
바로 그것이다. 에너지가 없으면
건강을 지탱할 수 없다.

- 캐롤라인 미스의 《영혼의 해부》중에서 -


더이상 에너지를 무의미하게 흘려보내지 말자.
...근데 에너지 용어가 뭐지..

지금은 내 곁에 없지만,
언제까지나 나의 고양이인 헐.
너무너무 예쁜 녀석 ㅠ_ㅠ
보들보들 따끈따끈 말랑말랑

지금쯤 남산 어딘가를 헤매고 있으려나
추웠던 이번 겨울도 잘 넘겼겠지?

전공관련도서들도 많지만 제외-_-;
일반인이 읽어도 괜찮을 듯한 책들.
그나마 교양도서라고 읽은 것들인데도 너무 치우쳤다.

양자 역학의 모험 김종오 2006.12.29
나름대로 기본부터 쓰려고 한 듯 하지만 그래도 뒷부분은 어려움

시간의 발견 Wilson, Colin 2006.12.27
시간이란 주제를 놓고 과학자 뿐 아니라 역사가, 철학자, 심리학자가 쓴 인문교양서.
시간을 처음 측정하게 된 계기, 바빌로니아 로마의 교황에 이르기까지 달력 만들기에 얽힌 이야기, 시계가 없었을 때 시간을 측정한 방법, 시계의 발명이 인간에 미친 영향, 분과 초의 계산 등 시간의 본질 문제를 여러 각도에서 살펴보고 있다.
- 누군가가 인터넷에서 돈 받고 파는 독후감의 일부-_-

유전자들의 전쟁 : 행동으로 본 사회생물학의 세계 이병훈 2006.12.27
사회생물학이라는 거 처음 알았다.
하지만 나에겐 그다지 흥미롭지 않았어.

유전자의 분자생물학 Watson, James D 2006.12.30
요 녀석 필독도서라 예약해 둔 거 찾으러 갔더니,
전공 도서냐.. 5센치가 넘는 두께의 압박.
거의 그림만 대충 봤음. 추천하고 싶지는 않다.

식물의 사생활 : 식물행동의 자연사 Attenborough, David 2006.12.27
사진이 페이지마다 가득 가득.
대부분의 사람들이 분명 처음 볼 듯한 식물들의 사진이 많다!
내용을 안 읽고 사진만 봐도 재밌을 듯. 난 다 읽었지만 ㅎㅎ

과학은 모든 의문에 답할 수 있는가 Brockman, John 2006.12.27
중 고등학생 필독도서로 선정될 듯한 내용 ㅎ
그냥 시간 남을 때 한 주제씩 읽어 보면 괜찮을 듯한 책. 적당히 재밌다.

(톰 피터스의) 미래를 경영하라 Peters, Thomas J 2006.11.28
사실 난 이런 책 관심이 없어서.
누가 추천해서 읽긴 했는데, 전혀 와 닿는게 없다.

時間의 歷史 Hawking, S. W 2007.01.09
책은 작은데 꽤 오래 걸린다.
몇번이고 봤던 내용들이었긴 하지만..
강추 강추
 
양자론 McEvoy, J. P 2006.12.29
그림이 많고 글이 별로 없는 건 좋은데.
이런 식으로 써 놓으면 대체 누가 이해한단 말인가.
이건 아니야~

(row´ter) (n.) A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP뭩 network. Routers are located at gateways, the places where two or more networks connect.

Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

Very little filtering of data is done through routers.


Definition: Routers are physical devices that join multiple wired or wireless networks together. Technically, a wired or wireless router is a Layer 3 gateway, meaning that the wired/wireless router connects networks (as gateways do), and that the router operates at the network layer of the OSI model.

Home networkers often use an Internet Protocol (IP) wired or wireless router, IP being the most common OSI network layer protocol. An IP router such as a DSL or cable modem broadband router joins the home's local area network (LAN) to the wide-area network (WAN) of the Internet.

By maintaining configuration information in a piece of storage called the "routing table," wired or wireless routers also have the ability to filter traffic, either incoming or outgoing, based on the IP addresses of senders and receivers. Some routers allow the home networker to update the routing table from a Web browser interface. Broadband routers combine the functions of a router with those of a network switch and a firewall in a single unit.

라우터는 동일한 전송 프로토콜을 사용하는 분리된 네트웍을 연결하는 장치로 네트웍 계층간을 서로 연결한다. 라우터는 브리지가 가지는 기능에 추가하여 경로 배정표에 따라 다른 네트웍 또는 자신의 네트웍 내의 노드를 결정한다. 그리고 여러 경로 중 가장 효율적인 경로를 선택하여 패킷을 보낸다. 라우터는 흐름제어를 하며, 인터네트웍 내부에서 여러 서브네트웍을 구성하고, 다양한 네트웍 관리 기능을 수행한다. 브리지와 라우터의 차이점을 간단히 살펴보면, 라우터는 네트웍 계층까지의 기능을 담당하고 있으면서 경로 설정을 해주는 반면, 브리지는 데이터링크 계층까지의 기능만으로 목적지 주소에 따른 선별 및 간단한 경로 결정을 한다.

라우터의 장점은 다음과 같다.

• 환경설정 가능 : 관리 방침에 따라 라우팅 방식이 결정, 전체 네트웍의 성능이 개선된다.
• 유지보수의 용이 : 알고리즘에 따라 자동으로 경로가 결정된다.
• 확장이 용이 : 네트웍 형상에 구애받지 않으므로 대규모 네트웍 구성이 용이하다.

라우터의 단점은 다음과 같다.

• 초기 환경설정이 어렵다.
• 특정 프로토콜이나 하위 프로토콜 지원이 불가능하고 복잡하므로 가격이 비싸다.

A router is an Intermediate System (IS) which operates at the network layer of the OSI reference model. Routers may be used to connect two or more IP networks, or an IP network to an internet connection.

A router consists of a computer with at least two network interface cards supporting the IP protocol. The router receives packets from each interface via a network interface and forwards the received packets to an appropriate output network interface. Received packets have all link layer protocol headers removed, and transmitted packets have a new link protocol header added prior to transmission.

The router uses the information held in the network layer header (i.e. IP header) to decide whether to forward each received packet, and which network interface to use to send the packet. Most packets are forwareded based on the packet's IP destination address, along with routing information held within the router in a routing table. Before a packet is forwarded, the processor checks the Maximum Transfer Unit (MTU) of the specified interface. Packets larger than the interface's MTU must be fragmented by the router into two or more smaller packets. If a packet is received which has the Don't Fragment (DF) bit set in the packet header, the packet is not fragmented, but instead discarded. In this case, an ICMP error message is returned to the sender (i.e. to the original packet's IP source address) informing it of the interface's MTU size. This forms the basis for Path MTU discovery (PMTU).

The routing and filter tables resemble similar tables in link layer bridges and switches. Except, that instead of specifying link hardware addresses (MAC addresses), the router table sepcify network (IP addresses). The routing table lists known IP destination addresses with the appropraite network interface to be used to reach that destiantion. A default entry may be specified to be used for all addresses not explicitly defined in the table. A filter table may also be used to ensure that unwanted packets are discarded. The filter may be used to deny access to particular protocols or to prevent unauthorised access from remote computers by discarding packets to specified destination addresses.

A router forwards packets from one IP network to another IP network. Like other systems, it determines the IP network from the logical AND of an IP address with the associated subnetwork address mask. One execption to this rule is when a router receives an IP packet to a network broadcast address. In this case, the router discards the packet. Forwarding broadcast packet can lead to severe storms of packets, and if uncontrolled could lead to network overload.

A router introduces delay (latency) as it processes the packets it receives. The total delay observed is the sum of many components including:

• Time taken to process the frame by the data link protocol
• Time taken to select the correct output link (i.e. filtering and routing)
• Queuing delay at the output link (when the link is busy)
• Other activities which consume processor resources (computing routing tables, network management, generation of logging information)

The router queue of packets waiting to be sent also introduces a potential cause of packet loss. Since the router has a finite amount of buffer memory to hold the queue, a router which receives packets at too high a rate may experience a full queue. In this case, the router ahs no other option than to simply discard excess packets. If required, these may later be retransmitted by a transport protocol.

Architecture of a router

Routers are often used to connect together networks which use different types of links (for instance an HDLC link connecting a WAN to a local Ethernet LAN). The optimum (and maximum) packet lengths (i.e. the maximum transmission unit (MTU)) is different for different types of network. A router may therefore uses IP to provide segmentation of packets into a suitable size for transmission on a network.

Associated protocols perform network error reporting (ICMP), communication between routers (to determine appropriate routes to each destination) and remote monitoring of the router operation (network management).

The operation of a simple modern router is described on a separate page. If you want to know how the router actually works click HERE.


Also see bridge , gateway , hub , and switch .

In packet-switched networks such as the Internet, a router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any gateway (where one network meets another), including each point-of-presence on the Internet. A router is often included as part of a network switch.

A router may create or maintain a table of the available routes and their conditions and use this information along with distance and cost algorithms to determine the best route for a given packet. Typically, a packet may travel through a number of network points with routers before arriving at its destination. Routing is a function associated with the Network layer (layer 3) in the standard model of network programming, the Open Systems Interconnection (OSI) model. A layer-3 switch is a switch that can perform routing functions.

An edge router is a router that interfaces with an asynchronous transfer mode (ATM) network. A brouter is a network bridge combined with a router.

For home and business computer users who have high-speed Internet connections such as cable, satellite, or DSL, a router can act as a hardware firewall. This is true even if the home or business has only one computer. Many engineers believe that the use of a router provides better protection against hacking than a software firewall, because no computer Internet Protocol address are directly exposed to the Internet. This makes port scans (a technique for exploring weaknesses) essentially impossible. In addition, a router does not consume computer resources as a software firewall does. Commercially manufactured routers are easy to install, reasonably priced, and available for hard-wired or wireless networks.


A router is a computer networking device that forwards data packets across a network toward their destinations, through a process known as routing. Routing occurs at Layer 3 (the network layer i.e. Internet Protocol (IP)) of the OSI seven-layer protocol stack.

Function

A router acts as a junction between two or more networks to transfer data packets among them. A router is different from a switch. A switch connects devices to form a local area network (LAN).

One easy illustration for the different functions of routers and switches is to think of switches as neighborhood streets, and the router as the intersections with the street signs. Each house on the street has an address within a range on the block. In the same way, a switch connects various devices each with its own IP address on a LAN.

However, the switch knows nothing about IP addresses except its own management address. Routers connect networks together the way that on-ramps or major intersections connect streets to both highways and freeways, etc. The street signs at the intersection (routing table) show which way the packets need to flow.

So for example, a router at home connects the Internet service provider's (ISP) network (usually on an Internet address) together with the LAN in the home (typically using a range of private IP addresses, see network address translation (NAT)) and a single broadcast domain. The switch connects devices together to form the LAN. Sometimes the switch and the router are combined together in one single package sold as a multiple port router.

In order to route packets, a router communicates with other routers using routing protocols and using this information creates and maintains a routing table. The routing table stores the best routes to certain network destinations, the "routing metrics" associated with those routes, and the path to the next hop router. See the routing article for a more detailed discussion of how this works.

Routing is most commonly associated with Internet Protocol(IP), although other less-popular routed protocols are in use.

A firewall is an information technology (IT) security device which is configured to permit, deny or proxy data connections set and configured by the organization's security policy. Firewalls can either be hardware and/or software based. A firewall's basic task is to control traffic between computer networks with different zones of trust. Typical examples are the Internet which is a zone with no trust and an internal network which is (and should be) a zone with high trust. The ultimate goal is to provide controlled interfaces between zones of differing trust levels through the enforcement of a security policy and connectivity model based on the least privilege principle and separation of duties. A firewall is also called a Border Protection Device (BPD) in certain military contexts where a firewall separates networks by creating perimeter networks in a Demilitarized zone (DMZ). In a BSD context they are also known as a packet filter. A firewall's function is analogous to firewalls in building construction. Proper configuration of firewalls demands skill from the firewall administrator. It requires considerable understanding of network protocols and of computer security. Small mistakes can render a firewall worthless as a security tool. 방화벽은 네트웍 게이트웨이 서버에 위치하고 있는 일련의 연관된 프로그램들로서, 다른 네트웍의 사용자들로부터 사설 네트웍의 자원들을 보호해준다 (이 용어는 보안정책과 함께 사용된 프로그램들에도 적용된다). 방화벽은 외부인이 자신의 공개되지 않은 자원에 접근하는 것을 막고, 자기회사의 직원들이 접속해야할 외부의 자원들을 통제하기 위해 기업의 인트라넷과 인터넷 사이에 설치된다. 기본적으로 방화벽은 라우터 프로그램과 밀접하게 동작함으로써, 모든 네트웍 패킷들을 그들의 수신처로 전달할 것인지를 결정하기 위해 검사하고, 여과한다. 또한 방화벽은 워크스테이션 사용자 대신 네트웍에 요청을 해주는 프럭시 서버의 기능을 아예 포함하거나 또는 함께 상호 협력하여 동작한다. 방화벽은 네트웍의 다른 부분들과는 별개로, 특별히 지정된 컴퓨터에 설치되는 경우가 많은데, 이는 들어오는 요구가 사설 네트웍 자원으로 곧바로 전달되지 않도록 하기 위한 것이다. 방화벽의 차폐방법에는 몇 가지가 있다. 단순한 방법 중 하나는 들어오는 요구가 받아들일만한(즉, 이전에 확인된) 도메인 이름이나 IP 주소로부터 오는 것인지를 확인하는 것이다. 이동중인 사용자들을 위해서는 보안접속절차나 인증확인 등을 통해 사설 네트웍에 원격접속 할 수 있도록 허용한다. 방화벽 제품들을 만드는 회사들이 꽤 있다. 방화벽에 포함되어야할 기능으로는, 사용기록, 보고, 공격이 시작된 시점에서의 자동경보, 그리고 방화벽의 제어를 위한 그래픽사용자 인터페이스 등이 있다.

(fīr´wâl) (n.) A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.

There are several types of firewall techniques:

Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.

Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.

Circuit-level gateway: Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.

Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.

In practice, many firewalls use two or more of these techniques in concert.

A firewall is considered a first line of defense in protecting private information. For greater security, data can be encrypted.

NIS is a distributed database that provides a repository for storing information about hosts, users, and mailboxes in the UNIX environment. It was originally developed by Sun Microsystems and called YP (Yellow Pages). NIS is used to identify and locate objects and resources that are accessible on a network.

NIS, which stands for Network Information Services, was developed by Sun Microsystems to centralize administration of UNIX® (originally SunOS™) systems. It has now essentially become an industry standard; all major UNIX like systems (Solaris™, HP-UX, AIX®, Linux, NetBSD, OpenBSD, FreeBSD, etc) support NIS.

NIS was formerly known as Yellow Pages, but because of trademark issues, Sun changed the name. The old term (and yp) is still often seen and used.

It is a RPC-based client/server system that allows a group of machines within an NIS domain to share a common set of configuration files. This permits a system administrator to set up NIS client systems with only minimal configuration data and add, remove or modify configuration data from a single location.

It is similar to the Windows NT® domain system; although the internal implementation of the two are not at all similar, the basic functionality can be compared.


NIS (Network Information System) is a network naming and administration system for smaller networks that was developed by Sun Microsystems. NIS+ is a later version that provides additional security and other facilities. Using NIS, each host client or server computer in the system has knowledge about the entire system. A user at any host can get access to files or applications on any host in the network with a single user identification and password. NIS is similar to the Internet's domain name system (DNS) but somewhat simpler and designed for a smaller network. It's intended for use on local area networks.

  네트워크 파일 시스템 (Network File System)의 약자로 정보 통신 네트워크에 접속 되어 있는 다른 컴퓨터의 파일 시스템을 고용하기 위한 분산 파일 공유 시스템 소프트웨어 이다. 컴퓨터의 기종이나 운영체제가 다른 환경의 컴퓨터에 분산되어 있는 파일을 공용하기 위한 것이다. 네트워크 파일 시스템이 탑재되어 있는 다른 컴퓨터상의 파일 시스템을 마치 자기의 컴퓨터에 있는 파일처럼 접근할 수 있으므로 파일 전송을 하고 나서 파일을 조작할 필요가 없다. 1985년에 미국의 썬 마이크로시스템즈 사가 개발 하였는데, 그 유용성 때문에 많은 시스템에서 이용할 수 있어 업계 표준과 같이 되었다. NFS는 개발사인 썬 마이크로시스템즈 사의 등록 상표이다.

  NFS 서비스를 제공하기 위해서는 NFS 서버와 클라이언트 간의 기보적인 요소를 갖추어야 하는데, 먼저 사용자 시스템에 NFS 클라이언트가 있어야하며, 원격지 컴퓨터에는 NFS 서버가 설치되어 있어야 한다. 둘 모두 TCP/IP 프로토콜이 설치 되어 있어야 한다. 초기에는 TCP 대신 UDP를 사용하기도 하였다. NFS 서버는 컴퓨터 간의 통신 방법으로 RPC(Remote Procedure Call)를 사용한다.

  NFS는 여러명이 같이 사용되는 대용량 프로그램이나 테이터들을 하나의 호스트에 넣어두고 단지 마운트를 통해서 서버의 자원을 자기 자원이양 똑같이 사용하는 것이 가능하다. 그러나 네트워크의 트래픽이 걸려 속도가 느려진다던지 혹은 보안의 허점이 생길 수도 있다는 것을 염두해 두어야 한다.

The Network File System (NFS) is a client/server application that lets a computer user view and optionally store and update file on a remote computer as though they were on the user's own computer. The user's system needs to have an NFS client and the other computer needs the NFS server. Both of them require that you also have TCP/IP installed since the NFS server and client use TCP/IP as the program that sends the files and updates back and forth. (However, the User Datagram Protocol, UDP, which comes with TCP/IP, is used instead of TCP with earlier versions of NFS.)

Among the many different file systems that FreeBSD supports is the Network File System, also known as NFS. NFS allows a system to share directories and files with others over a network. By using NFS, users and programs can access files on remote systems almost as if they were local files.

Some of the most notable benefits that NFS can provide are:

• Local workstations use less disk space because commonly used data can be stored on a single machine and still remain accessible to others over the network.

• There is no need for users to have separate home directories on every network machine. Home directories could be set up on the NFS server and made available throughout the network.

• Storage devices such as floppy disks, CDROM drives, and Zip® drives can be used by other machines on the network. This may reduce the number of removable media drives throughout the network.

NFS는 컴퓨터 사용자가 원격지 컴퓨터에 있는 파일을 마치 자신의 컴퓨터에 있는 것처럼 검색하고, 마음대로 저장하거나 수정하도록 해주는 클라이언트/서버형 응용프로그램이다. 사용자 시스템에는 NFS 클라이언트가 있어야하며, 다른 컴퓨터 (원격지의 컴퓨터)에는 NFS 서버가 설치되어 있어야 한다. 또한, 둘 모두 TCP/IP 프로토콜이 설치되어 있어야 하는데, 왜냐하면, NFS 서버와 클라이언트가 파일을 보내거나 수정하는 프로그램으로 TCP/IP를 사용하기 때문이다 (그러나, 초기버전의 NFS에서는 TCP 대신에 UDP가 사용되기도 한다). NFS는 썬마이크로시스템즈에 의해 개발되었으며, 파일서버의 표준으로 정착되었다. 이 프로토콜은 컴퓨터들 간의 통신 방법으로서 RPC를 사용한다. 윈도우 95와 썬(Sun)의 Solstice Network Client와 같은 제품을 사용하는 일부 운영체계에 NFS를 설치할 수 있다. NFS를 이용하여, 사용자나 시스템관리자는 파일시스템의 전부 또는 일부를 설치할 수 있다. 설치된(액세스할 수 있도록 지정된) 파일시스템은 각 사용자들의 권한에 따라 개개의 파일을 액세스할 수 있게된다. NFS는 인터넷 기술이 가미된 WebNFS로 확장되었으며, 이 제품과 제시된 표준안은 현재 넷스케이프 커뮤니케이터 브라우저의 일부이다. WebNFS는 썬마이크로시스템즈가 웹 페이지와 다른 인터넷 파일들을 빠르게 액세스할 수 있는 방법이라고 믿고 있는 바로 그것을 제공한다.

NFS, the network filesystem, is probably the most prominent network services using RPC. It allows to access files on remote hosts in exactly the same way as a user would access any local files. This is made possible by a mixture of kernel functionality on the client side (that uses the remote file system) and an NFS server on the server side (that provides the file data). This file access is completely transparent to the client, and works across a variety of server and host architectures.

NFS offers a number of advantages:

• Data accessed by all users can be kept on a central host, with clients mounting this directory at boot time. For example, you can keep all user accounts on one host, and have all hosts on your network mount /home from that host. If installed alongside with NIS, users can then log into any system, and still work on one set of files.
• Data consuming large amounts of disk space may be kept on a single host. For example, all files and programs relating to LaTeX and METAFONT could be kept and maintained in one place.
• Administrative data may be kept on a single host. No need to use rcp anymore to install the same stupid file on 20 different machines.

NFS is largely the work of Rick Sladkey, who wrote the NFS kernel code and large parts of the NFS server. The latter is derived from the unfsd user-space NFS server originally written by Mark Shand, and the hnfs Harris NFS server written by Donald Becker.

Let's have a look now at how NFS works: A client may request to mount a directory from a remote host on a local directory just the same way it can mount a physical device. However, the syntax used to specify the remote directory is different. For example, to mount /home from host vlager to /users on vale, the administrator would issue the following command on vale:

mount will then try to connect to the mountd mount daemon on vlager via RPC. The server will check if vale is permitted to mount the directory in question, and if so, return it a file handle. This file handle will be used in all subsequent requests to files below /users.

When someone accesses a file over NFS, the kernel places an RPC call to nfsd (the NFS daemon) on the server machine. This call takes the file handle, the name of the file to be accessed, and the user's user and group id as parameters. These are used in determining access rights to the specified file. In order to prevent unauthorized users from reading or modifying files, user and group ids must be the same on both hosts.

On most implementations, the NFS functionality of both client and server are implemented as kernel-level daemons that are started from user space at system boot. These are the NFS daemon (nfsd) on the server host, and the Block I/O Daemon (biod) running on the client host. To improve throughput, biod performs asynchronous I/O using read-ahead and write-behind; also, several nfsd daemons are usually run concurrently.

The NFS implementation of is a little different in that the client code is tightly integrated in the virtual file system (VFS) layer of the kernel and doesn't require additional control through biod. On the other hand, the server code runs entirely in user space, so that running several copies of the server at the same time is almost impossible because of the synchronization issues this would involve. NFS currently also lacks read-ahead and write-behind, but Rick Sladkey plans to add this someday.

The biggest problem with the NFS code is that the kernel as of version 1.0 is not able to allocate memory in chunks bigger than 4K; as a consequence, the networking code cannot handle datagrams bigger than roughly 3500 bytes after subtracting header sizes etc. This means that transfers to and from NFS daemons running on systems that use large UDP datagrams by default (e.g. 8K on SunOS) need to be downsized artificially. This hurts performance badly under some circumstances. This limit is gone in late -1.1 kernels, and the client code has been modified to take advantage of this.

The domain name system (DNS) stores and associates many types of information with domain names, but most importantly, it translates domain names (computer hostnames) to IP addresses. It also lists mail exchange servers accepting e-mail for each domain. In providing a worldwide keyword-based redirection service, DNS is an essential component of contemporary Internet use.

Useful for several reasons, the DNS pre-eminently makes it possible to attach easy-to-remember domain names (such as "wikipedia.org") to hard-to-remember IP addresses (such as 66.230.200.100). People take advantage of this when they recite URLs and e-mail addresses. In a subsidiary function, the domain name system makes it possible for people to assign authoritative names without needing to communicate with a central registrar each time.

The Domain Name System (abbreviated DNS) is an Internet directory service. DNS is how domain names are translated into IP addresses, and DNS also controls email delivery. If your computer cannot access DNS, your web browser will not be able to find web sites, and you will not be able to receive or send email.

The DNS system consists of three components: DNS data (called resource records), servers (called name servers), and Internet protocols for fetching data from the servers.

The billions of resource records in the DNS are split into millions of files called zones. Zones are kept on authoritative servers distributed all over the Internet, which answer queries based on the resource records stored in the zones they have copies of. Caching servers ask other servers for information and cache any replies. Most name servers are authoritative for some zones and perform a caching function for all other DNS information. Large name servers are often authoritative for tens of thousands of zones, but most name servers are authoritative for just a few zones.


The domain name system (DNS) is the way that Internet domain names are located and translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-remember "handle" for an Internet address.

Because maintaining a central list of domain name/IP address correspondences would be impractical, the lists of domain names and IP addresses are distributed throughout the Internet in a hierarchy of authority. There is probably a DNS server within close geographic proximity to your access provider that maps the domain names in your Internet requests or forwards them to other servers in the Internet.


Short for Domain Name System (or Service or Server), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.

The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

NIS and NIS+ (Network Information System)

NIS는 썬 마이크로시스템즈에서 개발된 소규모 네트웍용 네트웍 명명 및 관리 시스템이다. NIS+는 보안 및 편의 기능들을 추가한 그 후의 버전이다. NIS를 사용하면, 시스템 내의 각 호스트 클라이언트들이나 서버 컴퓨터가 전체 시스템을 인식한다. 어떤 호스트에 있는 사용자라도, 한 개의 사용자ID와 패스워드를 가지고 네트웍 상의 어떠한 호스트 상에 있는 파일들이나 프로그램들에도 접근할 수 있다 NIS는 인터넷의 DNS와 비슷하지만, 그보다는 다소 간단하고, 소규모 네트웍에 알맞게 설계되었다. 이 시스템은 근거리통신망 상에서 사용하는 것을 목적으로 만들어졌다. NIS는 호스트들 간의 통신을 위해 클라이언트/서버 모델과 원격절차호출 인터페이스를 사용한다. NIS는 하나의 서버와 클라이언트 프로그램 라이브러리, 그리고 약간의 관리도구들로 구성되어 있다. NIS는 종종 NFS와 함께 사용된다. NIS는 유닉스 기반의 프로그램이다. 비록 썬과 다른 회사들이 독점 버전을 공급하고는 있지만, 대부분의 NIS 코드는 공개되어 있으며, 프리웨어 버전들도 찾아볼 수 있다. NIS는 원래 "옐로우페이지"라고 불렸었지만, 그러나 누군가가 이미 그 이름에 관해 상표로 등록한 상태였기 때문에, NIS로 바꾸어 부르게 되었다. 그렇지만 아직도 가끔 옐로우페이지의 약어인 "YP"로 불리기도 한다. 썬은 자사의 워크스테이션 네트웍은 물론, 윈도우 PC 네트웍을 위한 솔루션으로 NFS 제품과 함께 NIS+를 제공한다.

Network Information System (abbreviation: NIS) is an information system for managing networks, such as electricity network, water supply network, gas supply network, telecommunications network.

NIS may manage all data relevant to the network, e.g.- all components and their attributes, the connectivity between them and other information, relating to the operation, design and construction of such networks.

NIS for electricity may manage any, some or all voltage levels- Extra High, High, Medium and low voltage. It may support only the distribution network or also the transmission network.

NIS may be built on top of a GIS (Geographical information system).

NIS is used for centralised Authentication. NIS shares all NIS users' home directories using NFS and we can access any NIS users from any client in the network.

The Network Information Service or NIS is Sun Microsystems’ “Yellow Pages” (YP) client-server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network.

Sun licenses this technology to virtually all other Unix vendors.

As the name “Yellow Pages” was a registered trademark in the United Kingdom of British Telecom PLC for their (paper) commercial telephone directory, Sun changed the name of their system to NIS, though all the commands and functions still start with “yp”.

NIS/YP is used for maintenance and distribution of a central directory of user and group information, hostnames, e-mail aliases and other text-based tables of information in a computer network. For example, in a common UNIX environment, the list of users for identification is placed in /etc/passwd, and secret authentication hashes in /etc/shadow. NIS adds another “global” user list which is used for identifying users on any client of the NIS domain.

Technically NIS can be configured to serve password data used to authenticate users against as well; however, not only is this cumbersome to do without resorting to DES encrypted passwords (which are known to be weak) if multiple OSs are in use, it also allows any NIS client to retrieve the whole password database for offline inspection. Kerberos was designed to handle authentication in a more secure manner.

In many environments other directory services, which may be considered to be more modern and secure than NIS, such as LDAP, have come to replace it. For example, the 'slapd' daemon generally runs as a non-root user, and SASL-based encryption of LDAP traffic is natively supported.

The nameserver functionality NIS or LDAP can provide is probably better handled by DNS servers when used on large LANs, leaving just site-wide identification information for NIS master and slave systems to serve. However, some functions such as the distribution of netmask information to clients, as well as the maintenance of e-mail aliases, may still be performed by NIS or LDAP.

당신이 LAN을 운영한다고 할 때, 일반적인 최종 목표는 유저들에게 투명한 네트웍 환경을 제공하는 것이다. 이를 위한 중요한 발판은 유저 계정 정보과 같은 핵심 데이터를 유지하는 일이다. 우리는 이전에, hostname resolution을 위해서 강력하고도 복잡한 DNS서벼스가 존재한다는 것을 본 바 있다. 그 외의 일을을 위한 특정 서비스는 존재하지 않는다. 게다가 당신이 그저 인터넷에 연결되지 않은 소규모 LAN을 운영하려 할 때, DNS는 관리상의 문제를 고려하자면 그리 유용성 있게 보이지 않는다.

이것이 바로 Sun에서 NIS(Network Information System)를 개발한 이유이다. NIS는, passwd와 group파일의 내용과 같은 정보를 당신의 네트웍 상에 있는 모든 호스트에 배포(distribute)하는데 사용하는 일반적인 데이터 베이스 억세스 기능을 제공한다. 이는 모든 호스트에 동일한 계정을 가지게하여 네트웍이 마치 단일 시스템처럼 보이게 한다. 이와 비슷하게, 호스트네임 정보 역시 NIS를 사용하여 /etc/hosts파일에서 네트웍 상의 모든 머신에게 배포할 수 있다.

NIS는 RPC를 기반으로 하고, 서버와 클라이언트 측 라이브러리, 그리고 몇가지 관리용 툴로 이루어져 있다. 원래, NIS는 Yellow Pages, 줄여서 YP라고 불리는데, 이는 이 서비스를 비공식적으로 지칭할 때 많이 쓰이는 이름이다. 반면, Yellow Pages는 British Telecom의 트레이드 마크이며, Sun 측에 그 이름을 포기할 것을 요구하고 있다. 뭐 다 그렇듯이, 이미 사람들 입에 붙어버린 YP는 NIS에 연관되 커맨드, 즉 ypserv, ypbind등과 같은 것들의 접두어로 남게되었다.

오를날 NIS는 거의 모든 Unice들에서 사용할 수 있으며, 무료 implementation 마저도 나와 있다. 하느는 BSD Net-2 릴리즈에서 유래한 것으로, Sun이 기증한 Publiv domain reference implementation을 계승한 것이다. 최근에야 NIS 관리용 프로그램이 Swen Thu:mmler에의해 리눅스로 포팅된 것과는 대조적으로, 이 릴리즈의 라이브러리 클라이언트 코드는 오래전부터 GNU libc에 내재되어 있었다. reference implementation에서는 NIS 서버가 제외되어 있었으나, Tobias Reber가 모든 툴과 서버를 지닌 새로운 NIS 패키지를 만들었으며, 이를 yps라 부른다.

현재, Peter Eriksson에 의해 완전히 재 코딩된 NIS 코드는 NYS라 불리며, 보통의 NIS와, Sun이 좀 더 수정을 가한 NIS+를 모두 지원한다. NYS는 NIS 툴셋과 서버를 지원할 뿐 아니라 언젠가는 표준 libc에 내재될 새로운 라이브러리 함수가 추가된 것이다. 이는 현재 hostname resolution을 하기위해 host.conf를 사용하는 구조 대신, 새로운 설정 구조를 지닌다. 이 기능에 대해선 나중에 논의할 것이다.

이 장은 "전통적인" NIS 코드라 말하는, 다른 두 패키지 보다는 NYS에 중점을 둔다. 만약 그 두 패키지 중 하나를 사용하고자 한다면 이 장의 설명은 충분할 수도, 불충분할 수도 있다. 추가적인 정보를 얻기위해선 Hal Stern의 NFS and NIS([Stern92]를 보라)와 같은 NIS에 대한 서적을 참고하라.

NYS는 아직 개발 중이며, 네트웍 프로그램이나 login 프로그램같은 표준 리눅스 유틸리티에도 NYS 설정구조가 반영되지 않았다. NYS가 main stream이라할 수 있는 libc에 포함되기 전까지는, 그것을 사용하기위해 이 모든 바이너리들을 재 컴파일 해야한다. 이러한 어플리케이션의 Makefile에, libc앞에 -lnsl을 마지막 옵션으로 linker에 지정하라. 이것은 표준 C 라이브러리대신 NYS 라이브러리인 libnsl에서 적절한 관련함수를 링크시킨다.

When you are running a local area network, your overall goal is usually to provide an environment to your users that makes the network transparent. An important stepping stone to this end is to keep vital data such as user account information synchronized between all hosts. We have seen before that for host name resolution, a powerful and sophisticated service exists, being DNS. For others tasks, there is no such specialized service. Moreover, if you manage only a small LAN with no Internet connectivity, setting up DNS may not seem worth the trouble for many administrators.

This is why Sun developed NIS, the Network Information System. NIS provides generic database access facilities that can be used to distribute information such as that contained in the passwd and groups files to all hosts on your network. This makes the network appear just as a single system, with the same accounts on all hosts. In a similar fashion, you can use NIS to distribute the hostname information form /etc/hosts to all machines on the network.

NIS is based on RPC, and comprises a server, a client-side library, and several administrative tools. Originally, NIS was called Yellow Pages, or YP, which is still widely used to informally refer this service. On the other hand, Yellow Pages is a trademark of British Telecom, which required Sun to drop that name. As things go, some names stick with people, and so YP lives on as a prefix to the names of most NIS-relate