(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
Routers give multiple machines access to the internet under one external IP address, whereas a switch is only a splitter. Compare the router to an intersection with street signs, and switches as neighborhood streets.
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.