Routers are key to your organization's WAN strategy. Here are some tips on buying these layer 3 boxes. by Mahesh Rathod

Routers are designed to link many network technologies, and are used in campus and enterprise networks

The "routing table" ensures that packets travel the most efficient paths to their destinations

A router is a device that operates at the Network Layer, or layer 3 of the OSI model. Routers are designed to link diverse network technologies, and are frequently used in large campus and enterprise networks. At the network layer of operation, you find a wider range of mechanisms that are designed to deal with the issues that can arise when building large network systems. By operating at the network layer, routers can easily deal with computers attached to everything from slow serial links to high-speed LAN systems.

In sufficiently large and complex networks, and especially networks with multiple network technologies, you may wish to use a router for the benefits it can bring. Many vendors provide routers with multi-protocol capabilities, making it possible to deal with various protocols in a single device.

Purpose of routers

Routers are primarily used to connect two or more IP networks, or an IP network to Net. A router consists of a computer with at least two NICs (network interface cards) that support the IP protocol. The router receives a packet from one NIC and forwards the received packets to an appropriate output NIC.

Routers forward packets based on the packet's IP destination address, along with routing information held within the router in a routing table. A network road map that routers use, ensure that packets reach their destinations using the most efficient paths. If a link between two routers fails, the sending router can determine an alternate route to keep traffic moving.

Flavors

Routers can be classified on their functionality or the applications they can be used for.

Based on their function, routers can be classified as static and dynamic. Static routers choose the shortest way to the destination and are cheaper. Dynamic routers choose the best way to the destination after taking network traffic into consideration.

Based on applications, routers can be of three types: access, backbone and IP aware switches. Access routers can be seen as Internet gateways, where packets are classified and traffic is policed to ensure that flows do not violate their assigned bandwidths. Backbone routers take care of large amounts of aggregated IP traffic, at very high speeds. IP aware switches use IP addresses to switch the packets on to and between different local area networks.

Routers or Switches?
Routers are typically used to connect workgroups to the backbone. Here fiber optic cables are used for backbones, with ATM, token ring or Ethernet as the networking technology. Routers also form the central point for connecting a company's different sites together over a WAN, using technologies such as Frame Relay, leased lines, X.25 and ATM.

In WAN environments, routers play a more crucial role than switches do. Routers not only effectively manage range of WAN technologies, but also make optimal use of WAN resources through intelligent path selection.

Within the network core, Ethernet switches are generally used to segment workgroup network. They provide dedicated bandwidth to servers, high-performance users, and smaller groups of end users.

Router features

Here's a list of some of the key features you need to consider when buying a router.

Multiple network protocol support:
Enterprises need the flexibility of working with multi-protocol networks, since they communicate with diverse hardware and software from many vendors. Routers need to support various standard networking protocols such as:

• TCP/IP
• Novell IPX
• AppleTalk (Phase 1 and Phase 2)
• Banyan VINES
• Xerox's Universal Protocol (PUP)
• X.25 protocols
• Frame Relay serial encapsulation
• Point-to-Point Protocol (PPP)

Support for standard media:
Routers need to support the following industry-standard networking media:

• Synchronous serial V.35, RS-232, and RS-449
• Ethernet IEEE 802.3 and Type II
• FDDI Single and dual mode
• Token Ring IEEE 802.5
• High-Speed Serial Interface (HSSI) T3 rates

Multiple routing protocol support:
Routers should be able to support various routing protocols such as:

• Network Address Translation
• Open Shortest Path First
• Hot Standby Router Protocol (HSRP)
• Border Gateway Protocol (BGP)
• Enhanced Interior Gateway Routing Protocol

Carrier class reliability:
Routers should be able to assure the highest possible reliability and network availability, as these are the needs of ISP and enterprise networks. Automatic switchover capability allows the router to operate without data or connection loss in the event of primary component failures.

QoS features:
In today's application intensive IP networks, the ability to control quality of service (QoS) becomes increasingly important. Routers should have hardware-based QoS controls and features that enable a network administrator to easily control and manage network traffic and applications with no degradation in system performance.

Flexible management:
Network administrators should be able to manage the router by using CLI (command line interface), Web browser or GUI (graphical user interface). The network management system must be able to provide centralized status, statistics monitoring, and traffic management.

Mahesh Rathod can be reached at rathodmp@hotmail.com