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Network Routing and Switching Basics

Routing

Routing is a term used to describe how a network moves packets from station A to station B. The packets move through a series of routers, each router progressing the packets from one machine to another progressing it to the destination.

Routing Protocols

Routing protocols [such as RIP, OSPF] help each machine understand where the next machine is that represents the next hop the packet must take.

Routers use the routing protocols to construct routing tables, located in the packet header. When a router receives a packet it looks at the routing table to identify the destination IP address, and determines the next router to hand it off to.

Switching

Switching is the transfer of data from an input to an output port of a machine, where the selection of the output port is based on Layer 2 [such as ATM VPI/VCI or Frame Relay DLCI] information.

Simple applications such as file transfer [FTP] and remote login only require a simple software based router platform, with network interfaces to support the existing T1/E1 or T3/E3 based backbones.

Higher speed and higher bandwidth transmissions require devices with capabilities to switch at the Layer-2 [data link] and the Layer-3 [network layer] in hardware.

Layer-2 switching devices - resolve the switching bottlenecks within the subnets of a LAN environment.

Layer-3 switching devices - alleviate the bottleneck in Layer-3 routing by moving the route lookup for Layer-3 forwarding to high speed switching hardware.

These solutions only support the fast packet transfer across the network. They do not address the service requirements of the information contained in the packets, nor account for additional metrics such as delay, jitter, and traffic congestion which can diminish network performance.

Label Switching

A short, fixed-length, easily processed label provides a shorthand representation of an IP packet's header, just as a ZIP code provides in a postal address.

Label switching solutions are categorized based on their use of label swapping packet forwarding combined with IP control protocols and a label distribution mechanism.

Different techniques are distinguished by the differences in the details.

See: IP Packet Switching

See: Multi-Protocol Layered Switching - the integration of Layer 2 switching and Layer 3 routing.

Next: IP Packet Switching