Router is a network device that forwards packets of data between computer networks. Routers perform the function of directing traffic on the Internet. A data packet is usually routed from one router to another through a network that forms an internetwork until it reaches the destination node.
The router is connected to two or more data lines from different networks. When a data packet enters one path, the router reads the network address information in the packet to determine its final destination. Then, using the information in the routing table or routing policy, direct the packet to the next network on its way.
The most familiar type of router is the home and small office routers that only forward IP packets between the home computer and the Internet. An example of a router is the owner's cable or DSL router, which connects to the Internet through an Internet service provider (ISP). More sophisticated routers, such as enterprise routers, connect large businesses or ISP networks to powerful core routers that forward data at high speed along the backbone fiber-optic line of the Internet. Although routers are usually specialized hardware devices, software-based routers also exist.
Video Router (computing)
Operasi
When multiple routers are used in an interconnected network, routers can exchange information about destination addresses using routing protocols. Each router builds a routing table a preferred route list between two systems on an interconnected network.
The router has two types of network element components organized into a separate plane :
- Control fields: The router maintains a routing table that specifies which route to use to forward packets, and through a physical interface. This is done using pre-configured internal directives, called static routes, or by studying routes dynamically using routing protocols. Static and dynamic routes are stored in the routing table. The field-control logic then strips the non-essential directives from the table and builds the forwarding information base (FIB) for use by the forwarding plane.
- The forwarding field: The router forwards the data packet between incoming and outgoing interface connections. This forwards them to the correct network type using the information that the packet header contains is suitable for entries in FIB provided by the control plane.
Maps Router (computing)
Apps
Routers may have interfaces for different types of physical layer connections, such as copper cables, fiber optics, or wireless transmissions. It can also support different network layer transmission standards. Each network interface is used to allow data packets to be forwarded from one transmission system to another. Routers can also be used to connect two or more logical groups of computer devices known as subnets, each with a different network prefix.
Routers can provide connectivity within a company, between a company and the Internet, or between an Internet service provider's network (ISP). The largest routers (such as Cisco CRS-1 or Juniper PTX) connect various ISPs, or can be used in large enterprise networks. Smaller routers typically provide connectivity for typical home and office networks.
All sizes of routers can be found within the company. The most powerful routers are usually found in ISPs, academic and research facilities. Large businesses may also require a stronger router to cope with the growing demand for intranet data traffic. The hierarchical internetworking model for router interconnection in large networks is commonly used.
Access, core and distribution
Access routers, including small office/home office models (SOHO), are located at home and customer sites such as branch offices that do not require their own hierarchical routing. Usually, they are optimized for low cost. Some SOHO routers are able to run free alternative Linux-based firmware such as Tomato, OpenWrt, or DD-WRT.
In the enterprise, core routers can provide a "collapsed backbone" that connects the distribution level routers of multiple campus buildings, or large enterprise locations. They tend to be optimized for high bandwidth, but do not have some features of the edge router.
The distribution router combines traffic from multiple access routers, either on the same site, or to collect data streams from multiple sites to large enterprise locations. Distribution routers are often responsible for enforcing service quality across a wide area network (WAN), so they may have sufficient installed memory, multiple WAN interface connections, and a substantial onboard data processing routine. They can also provide connectivity to another file server or external network group.
Security
External networks should be considered carefully as part of the overall local network security strategy. Routers may include firewalls, VPN handling, and other security functions, or these can be handled by a separate device. Many companies produce security-oriented routers, including Cisco PIX series, Cisco Meraki MX series and Juniper NetScreen. Routers also typically perform network address translation, (which allows multiple devices on a network to share a single public IP address) and a confidential packet inspection. Some experts argue that open source routers are more secure and reliable than closed source routers because open source routers allow errors to be quickly discovered and repaired.
Route various networks
Routers are also often differentiated based on the network in which they operate. Routers in a local area network (LAN) of one organization are called interior routers. An external router directs packets between hosts in one LAN and hosts on another LAN. A router operated in the backbone of the Internet is described as an exterior router. While the router that connects LAN with wide area network (WAN) is called a border router, or gateway router.
Internet connectivity and internal usage
Routers aimed at ISPs and large enterprise connectivity usually exchange routing information using Border Gateway Protocol (BGP). RFC 4098 standard defines the type of BGP router according to its function:
- Edge routers : Also called edge provider routers, are placed on the edge of an ISP network. Routers use External BGP for EBGP routers in other ISPs, or large enterprise Autonomous Systems.
- edge router Customers : Also called Customer Edge routers, located at the edge of the customer's network, also use EBGP to the provider's Autonomous System. This is usually used in organizations (companies).
- Inter-provider border router : ISP interconnection, is a BGP router that manages BGP sessions with other BGP routers in the ISP Autonomous System.
- The core router: A core router is in the Autonomous System as the backbone to carry traffic between edge routers.
- In ISP: In the Automated ISP System, routers use internal BGP to communicate with other ISP edge routers, other core intranet routers, or border routers of the ISP's intranet provider.
- "Internet backbone:" The Internet no longer has a clearly identifiable backbone, unlike its predecessor network. View the default-free zone (DFZ). The main ISP system routers form what can be considered the core of the current Internet backbone. The ISP operates all four types of BGP routers described here. ISP's core router is used to connect edge routers and borders. The core router may also have a special function in a virtual private network based on a combination of BGP protocol and the Multi-Protocol Label Protocol.
- Port forwarding: Routers are also used for port forwarding between servers connected to the private Internet.
- Voice/Data/Fax/Video Router: Usually referred to as an access server or gateway, this device is used to route and process voice, data, video and fax traffic across the Internet. Since 2005, most long distance phone calls have been processed as IP traffic (VOIP) through a voice gateway. The use of router access server type is expanded with the advent of the Internet, first with dial-up access and other revivals with voice telephone service.
- Larger networks typically use multilayer switches, with layer 3 devices used to connect only multiple subnets within the same security zone, and higher switch layers when filtering, translating, load balancing or higher level functions are required, especially between zones.
Historical and technical information
The concept of "Computer Interface" was first used by Donald Davies for the NPL network in 1966. The Interface Message Processor (IMP), created in 1967 for use in ARPANET, has the same functionality as the current routers do. The idea for a router (called a "gateway" at the time) originally emerged through a group of international computer network researchers called the International Networking Working Group (INWG). Formed in 1972 as an informal group to consider the technical issues involved in connecting different networks, it became the subcommittee of the International Federation for Information Processing later that year. This gateway device is different from the previous packet switching scheme in two ways. First, they connect different types of networks, such as serial lines and local area networks. Secondly, they are unrelated devices, which have no role in ensuring that traffic is delivered reliably, leaving it completely to the host.
This idea is explored in more detail, with a view to producing a prototype system as part of two simultaneous programs. One of these is the initial DARPA program, which creates the current TCP/IP architecture. The other is the program at Xerox PARC to explore new network technology, which generates the packet PARC Universal Packet; because of corporate intellectual property worries, he had gotten little attention outside Xerox for years. Some time after the beginning of 1974, the first Xerox router started to operate. The first true IP router was developed by Ginny Strazisar at BBN, as part of DARPA's efforts, during 1975-1976. By the end of 1976, three PDP-11 based routers worked in an experimental Internet prototype.
The first multiprotocol routers were independently created by staff researchers at MIT and Stanford in 1981; the Stanford router is done by William Yeager, and MIT by Noel Chiappa; both are also based on PDP-11. Most networks now use TCP/IP, but multiprotocol routers are still produced. They are important in the early stages of computer network growth when protocols other than TCP/IP are in use. Modern Internet routers that handle IPv4 and IPv6 are multiprotocol but are simpler devices than routers that process AppleTalk, DECnet, IP, and Xerox protocols.
From the mid-1970s and in the 1980s, general purpose minicomputers served as routers. High-speed modern routers are highly specialized computers with additional hardware added to speed up both common routing functions, such as packet forwarding, and special functions such as IPsec encryption. There are many uses of Linux and Unix based software, running open source routing code, for research and other applications. The Cisco IOS operating system is designed independently. Major router operating systems, such as Junos and NX-OS, are widely modified versions of Unix software.
Forwarding
The router's main purpose is to connect multiple networks and forward packets destined for its own network or other networks. The router is considered a 3-layer device because its main redirection decision is based on information in layer 3 IP packets, specifically the destination IP address. When the router receives the packet, it searches the routing table to find the best match between the destination IP address of the packet and one of the addresses in the routing table. Once a match is found, the packet is encapsulated in the layer-2 data link frame for the exit interface shown in the table entry. Routers do not normally look to packet payloads, but only on layer-3 addresses to make forwarding decisions, plus other optional information in the header for instructions, for example, quality of service (QoS). For pure IP forwarding, routers are designed to minimize state information associated with individual packets. Once the packet is forwarded, the router does not store any historical information about the package.
The routing table itself can contain information coming from various sources, such as manually configured default or static routes, or dynamic routing protocols where routers learn to route from other routers. The default route is the route used to route all traffic whose destination does not appear in the routing table; this is common - even required - on a small network, such as a home or small business where the default route only sends all non-local traffic to an Internet service provider. The default route can be configured manually (as a static route), or studied by dynamic routing protocols, or obtained by DHCP.
A router can run more than one routing protocol at a time, especially if it serves as an autonomous system border router between parts of the network that run different routing protocols; if so, then redistribution can be used (usually selectively) to share information between different protocols running on the same router.
In addition to making decisions about which interface the packet is routed to, which is handled primarily through the routing table, the router must also manage bottlenecks when the packet arrives at a higher level than the router can process. Three commonly used policies on the Internet are tail reduction, random early detection (RED), and random weighted early detection (WRED). The decline of the tail is the simplest and easiest to apply; the router simply drops the new packet entry after the queue length exceeds the buffer size in the router. RED probabilistically drops the initial datagram when the queue exceeds the pre-configured portion of the buffer, until the max is predetermined, when it becomes a tail drop. WRED requires the average weight of the queue size to act when traffic is almost over the pre-configured size, so short bursts will not trigger random dashes.
Another function that the router does is decide which packages should be processed first when there are multiple queues. This is managed through QoS, which is very important when Voice over IP is used, so as not to introduce excessive latency.
But another function that the router does is called policy-based routing where a custom rule is created to override rules derived from the routing table when a package delivery decision is made.
The router functions can be done through the same internal path that packets run inside the router. Some functions can be done through application-specific integrated circuits (ASIC) to avoid CPU time scheduling overhead for packet processing. Others may have to be done through the CPU because these packages require special attention that ASIC can not handle.
See also
- DECbit
- Mobile broadband modem
- Modem
- Residential gates
- TCAM Contentable addressable memory (hardware acceleration from route search)
- Wireless router
Note
References
External links
- The Internet Engineering Task Force, Last Routing Area checked Jan. 21, 2011.
Source of the article : Wikipedia
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