What are Routers?

What are Routers ?

Routers

A router is a communication device that is used to connect two logically and physically different networks, two LANs, two WANs and a LAN with WAN.  The main function of the router is to sorting and the distribution of the data packets to their destinations based on their IP addresses. Routers provides the connectivity between the enterprise businesses, ISPs and in the internet infrastructure, router is a main device.  Cisco routers are widely used in the world.  Every router has routing software, which is known as IOS.  Router operates at the network layer of the OSI model.  Router does not broadcast the data packets. 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.

Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router. The term "layer 3 switches" often is used interchangeably with router, but switch is a general term without a rigorous technical definition. In marketing usage, it is generally optimized for Ethernet LAN interfaces and may not have other physical interface types. In comparison, a network hub does not do any routing; instead every packet it receives on one network line gets forwarded to all the other network lines.

For most home users, they may want to set-up a LAN (local Area Network) or WLAN (wireless LAN) and connect all computers to the Internet without having to pay a full broadband subscription service to their ISP for each computer on the network. In many instances, an ISP will allow you to use a router and connect multiple computers to a single Internet connection and pay a nominal fee for each additional computer sharing the connection. This is when home users will want to look at smaller routers, often called broadband routers that enable two or more computers to share an Internet connection. Within a business or organization,  you may need to connect multiple computers to the Internet, but also want to connect multiple private networks — and these are the types of functions a router is designed for.

Image ; A Typical Router Connection 

Types Of Routers

Routers may provide connectivity inside enterprises, between enterprises and the Internet, and inside Internet Service Providers (ISP). The largest routers (for example the Cisco CRS-1 or Juniper T1600) interconnect ISPs, are used inside ISPs, or may be used in very large enterprise networks. The smallest routers provide connectivity for small and home offices.

Routers for Internet connectivity and internal use

Routers intended for ISP and major enterprise connectivity will almost invariably exchange routing information with the Border Gateway Protocol (BGP). RFC 4098 defines several types of BGP-speaking routers:

• Edge Router: Placed at the edge of an ISP network, it speaks external BGP (eBGP) to a BGP speaker in another provider or large enterprise Autonomous System (AS).
• Subscriber Edge Router: Located at the edge of the subscriber's network, it speaks eBGP to its provider's AS(s). It belongs to an end user (enterprise) organization.
• Inter-provider Border Router: Interconnecting ISPs, this is a BGP speaking router that maintains BGP sessions with other BGP speaking routers in other providers' ASes.
• Core router: A router that resides within the middle or backbone of the LAN network rather than at its periphery.

Within an ISP: Internal to the provider's AS, such a router speaks internal BGP (iBGP) to that provider's edge routers, other intra-provider core routers, or the provider's inter-provider border routers.

"Internet backbone:" The Internet does not have a clearly identifiable backbone, as did its predecessors. See default-free zone (DFZ). Nevertheless, it is the major ISPs' routers that make up what many would consider the core. These ISPs operate all four types of the BGP-speaking routers described here. In ISP usage, a "core" router is internal to an ISP, and used to interconnect its edge and border routers. Core routers may also have specialized functions in virtual private networks based on a combination of BGP and Multi-Protocol Label Switching (MPLS).

Routers are also used for port forwarding for private servers.

Small Office Home Office (SOHO) connectivity

Residential gateways (often called routers) are frequently used in homes to connect to a broadband service, such as IP over cable or DSL. A home router may allow connectivity to an enterprise via a secure Virtual Private Network.

Image ; Small Office Home Office Routers (SOHO)

While functionally similar to routers, residential gateways use port address translation in addition to routing. Instead of connecting local computers to the remote network directly, a residential gateway makes multiple local computers appear to be a single computer.

Enterprise routers

All sizes of routers may be found inside enterprises. The most powerful routers tend to be found in ISPs and academic & research facilities. Large businesses may also need powerful routers.

A three-layer model is in common use, not all of which need be present in smaller networks.

Access

Access routers, including SOHO, are located at customer sites such as branch offices that do not need hierarchical routing of their own. Typically, they are optimized for low cost.

Image; A Typical Router Setup

Distribution

Distribution routers aggregate traffic from multiple access routers, either at the same site, or to collect the data streams from multiple sites to a major enterprise location. Distribution routers often are responsible for enforcing quality of service across a WAN, so they may have considerable memory, multiple WAN interfaces, and substantial processing intelligence.

They may also provide connectivity to groups of servers or to external networks. In the latter application, the router's functionality must be carefully considered as part of the overall security architecture. Separate from the router may be a Fire walled or VPN concentrator, or the router may include these and other security functions.

When an enterprise is primarily on one campus, there may not be a distinct distribution tier, other than perhaps off-campus access. In such cases, the access routers, connected to LANs, interconnect via core routers.

Core

In enterprises, a core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations. They tend to be optimized for high bandwidth.

When an enterprise is widely distributed with no central location(s), the function of core routing may be subsumed by the WAN service to which the enterprise subscribes, and the distribution routers become the highest tier.

Image ; Enterprise Router (Juniper)

The enterprise router comes in many different forms. A fixed configuration is typical for small offices. Larger modular routers that allow for the addition of new interface and services cards add to the complexity of the system. The need for high performance, increased integration of common peripherals, small footprint, and lower power consumption are all important design considerations.

A variety of functions need to be performed including routing, forwarding and servicing. These functions often are segregated into different devices often called control plane, and data plane, although both can be done in a highly integrated device for smaller fixed configuration devices.

The control plane usually performs functions such as running the routing protocols, system management, and system control function. The data plane is more focused on doing protocol recognition and in many cases conversion while keeping the different interfaces running at wire speed

 

Sample Price of routers :-

ROUTER	PORTS	FEATURES	PRICE
NetGear RP614 Cable/DSL Router	4	Smart Wizard set-up, NAT firewall, up to 253 Network Users, Web site blocking, free network cable & stand.	$40
NetGear VPN Firewall Router FR328S	8	Analog modem back-up, True Firewall (DoS protection and SPI), URL filtering, logging, reporting, NAT routing, VPN pass-through, high-speed CPU for faster throughput.	$60
Linksys broadband Router with Phone Ports RT41P2-AT	4	2 voice ports for analog phones or faxes, Universal Plug-and-Play, NAT firewall,  supports DHCP	$125
Linksys EtherFast Cable/DSL - BEFSR81	8	NAT firewall, supports QOS, DHCP, Universal Plug-and-Play, URL blocking,	$70
D-Link Wireless Cable/DSL Router DI-624	4	802.11x, Indoors: Up to 328 feet (100 meters), WPA .Wi-Fi Protected Access, multichannel, AES encryption , compatible with all 2.4GHz devices	$73

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