Router Guide

A simple definition of the router is a networking device that is typically used to connect or segment the networks. This router guide discusses the routers in general, the types, what router you need, and how you can connect them. For a more detail about the hardware router as general can be found in the networking router article.

In this router guide, firstly we need to understand the general function of the router. The routers are mostly used in networks with the TCP/IP (Transmission Control Protocol /Internet Protocol) suites, for example the global Internet which is a large routed network. Routers can be used either to connect many smaller LAN networks into a larger network called an internetwork or to segment a large network into smaller sub-networks in order to improve performance or manageability. Routers are also sometimes used to join dissimilar media, such as unshielded twisted-pair (UTP) cabling and fiber-optic cabling, and different network architectures, such as Token Ring and Ethernet. See also how to calculate subnet networks in designing the subnet networks.

The routers typically connect multiple sites or branch offices to link them together in big inter-networking via WAN (wide area network) cloud. WAN connections types are normally dictated by the WAN service provider, and relate to the physical interface used by the connecting router. Numerous connection types exist, but when possible connections should be made using technologies that support higher data rates and support flexible configurations. Many carriers offer connection choices when provisioning WAN services. There are many WAN services available in the market such as Frame relay network, ISDN network; Point-to-point leased line and so on. More detail about many types of WAN technologies will not be discussed in this router guide.

Routers can also be used to connect local area networks (LANs) to telecommunication services such as leased lines or Digital Subscriber Line (DSL). A router used to connect a LAN to a leased line such as a T1 line is often called an access server, and a router used to access DSL servers is known as a DSL router. These routers often support basic firewall functionality to filter out packets based on their source or destination network address. Such a device is sometimes called a packet-filtering router. Home routers generally used by home users that are typically an all-in-one device that combines the function of a modem (Cable or DSL), router/firewall, a LAN switch, and a wireless access point (for wireless home routers). There are two types of home routers that have built-in modem: a Cable Wireless modem (such as Motorola SURFboard SBG900 Wireless Cable modem) and a DSL Wireless modem (such as DSL2640 D-Link).

Routers generally block broadcast traffic and can thus prevent broadcast storms from slowing down the flow of traffic in a network. Routers are so complex that Cisco Systems, the major vendor of enterprise-level routers, has developed an operating system called Internetwork Operating System (IOS) that is devoted solely to managing routers. See also STP protocols that control the broadcast storm.

Router Types

Routers types can be one of the following:

• Static routers: These must have their routing tables configured manually with all network addresses and paths within the internetwork. See also static route that discusses more detail about the static routing.
• Dynamic routers: These automatically create their routing tables by listening to network traffic and communicating with other routers by using such kinds of dynamic routing protocols such as Cisco EIGRP routing protocols, or OSPF an industrial routing protocols.

Comparison

Routers are similar to network bridges in that they both forward packets and can be used to either segment or join networks. However, routers use Layer 3 (network layer) addresses such as IP addresses to forward packets, but bridges employ Layer 2 addresses (MAC addresses) for this purpose.

When should you use a bridge and when should you use a router? Use bridges to connect network segments that run the same network protocol- for example, to connect an IP segment to an IP segment. Also use bridges when you run legacy non-routable network protocols such as NetBEUI on your network. On the other hand, use routers to connect network segments that run different network protocols-for example, to connect an IP segment to an Internetwork Packet Exchange (IPX) segment. In modern LAN Switches that supports VLANs that allow performing inter-VLAN communications – the use of layer 3 Switching is common in enterprise class LAN environments.

Generally speaking, routers are more intelligent than bridges and improve network bandwidth by not forwarding broadcast packets to other networks. Finally, use routers when you want to connect your network to the Internet.

Implementation

Routers work at the network layer (Layer 3) of the Open Systems Interconnection (OSI) reference model. They forward packets between networks on the basis of their destination logical addresses (IP addresses in the case of TCP/IP). Routers also route packets based on the available paths and their costs, thus taking advantage of redundant paths that can exist in a mesh topology network. To do this, routers contain internal tables called routing tables that keep track of the paths that packets can take as they move across the internetwork, along with the cost of reaching each remote network.

Because routers operate at a higher OSI level than bridges do, they have more powerful switching and filtering capabilities. They also generally require greater processing power, which results in routers usually costing more than bridges. Also, because routers use network addresses for routing packets, they can only work if the network protocol is a “routable protocol” such as TCP/IP or Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX). This is different from bridges, which are basically protocol-independent Layer 2 devices.

Connection

Routers can have multiple network interfaces which are typically have Serial interface (which connects to the WAN or to the internet) and Ethernet interface (which typically connect to the perimeter / private network).

For home wireless routers which have built-in modem (Cable or DSL), connection and configuration is very simple. They have typically two main ports: WAN port (that connect direct to the DSL or Cable line) and LAN Port(s) (which connect direct to the computers in home).

More detail discussion about the router connection will not be discussed in this router guide.

Ref: Cisco.Com internetworking

See also:

• Introduction about SonicWall Tz210 Series
• Understanding firewall ports
• How to choose the best home wireless routers for your need