Hemang KothariAssistant Professor

Computer Engineering Department MEFGI, Rajkot.

Email: hemang.kothari@marwadieducation.edu.in

Internetworking Devices

Internetworking Devices

• Internetworking devices are products used to connect networks.

• As computer network grows in size and complexity, so do the internetworking devices used to connect them.

Broadly, following are the Internetworking devices:

• Repeaters

• Hubs

• Bridges

• Switches

• Routers

• Gateways

• Networking devices are used to construct networks.

• Example: A local area Network (LAN) may need to cover more distance that its media can handle effectively. In this case, you can use a repeater to regenerate the signal.

• Internetworking devices are used to connect networks.

• Example: If you want to link a LAN into an internet, you need an internetworking device as a router or a gateway.

• An internet is an interconnection of individual networks.

Connecting Devices and the OSI Model

Connecting Devices

Connecting DevicesConnecting Devices

Repeaters

Hubs

Bridges

Two-Layer Switches

Connecting devices

Repeaters• A repeater (or regenerator) is an electronic device that operates

on only the physical layer of the OSI model.

• A repeater installed on a link receives the signal before it becomes too weak or corrupted, regenerates the original pattern, and puts the refreshed copy back on the link.

Repeaters

• A repeater does not actually connect two LANS; it connects two segments of the same LAN.

• A repeater forwards every frame; it has no filtering capability.

Hubs

• A Hub is a multiport repeater. It is normally used to create connections between stations in a physical star topology.

Bridges

• Bridges operate in both the physical and the data link layers of the OSI model.

Bridges

• Bridges can divide a large network into smaller segments. They contain logic that allows them to keep the traffic on each segment separate. When a frame (or packet) enters a bridge, the bridge not only regenerates the signal but checks the destination address and forwards the new copy only to the segment the address belong.

Bridges

• A bridge operates in both the physical and the data link layers.

• As a physical layer device, it regenerates the signal it receives.

• As a data link layer device, the bridge can check the physical (MAC) address (source and destination) contained in the frame.

• A bridge has filtering capability. It can check the destination address of a frame and decide if the frame should be forwarded or dropped. If the frame is to be forwarded, the decision must specify the port.

• A bridge does not change the physical (MAC) addresses in a frame.

• A bridge has a table used in filtering decisions.

Bridge

Types of Bridges

• To select between segments, a bridge must have a look-up table that contains the physical addresses of every station connect to it. The table indicate to which segment each station belongs.

Simple Bridge• The address table must be entered manually, before a

simple bridge can be used.• Whenever a new station is added or removed, the table

must modified.• Installation and maintenance of simple bridges are time-

consuming and potentially more trouble than the cost savings are worth.

Types of Bridges

Multiport bridges

A multiport bridge can be used to connect more than two LANs.

Transparent Bridges

• A transparent, or learning, bridge builds its table of station addresses on its own as it performs its bridge functions.

• If a transparent bridge is added or removed from the system, reconfiguration of the stations is unnecessary.

• A transparent bridge must meet following criteria:

1. Frames must be forwarded from one station to another.

2. The forwarding table is automatically made by learning frame movements in the network.

Learning Bridge

Loop Problem• Transparent bridges work fine as long as there are no

redundant bridges in the system.

• Bridges are normally installed redundantly, which means that two LANs may be connected by more than one bridge. In this case, if the bridges are transparent bridges, they may create a loop, which means a packet may be going round and round, from one LAN to another and back again to the first LAN.

• To solve the looping problem, the IEEE specification requires that bridges use the spanning tree algorithm to create a loopless topology.

Spanning Tree

• A spanning tree is a graph in which there is no loop.

• In a bridged LAN, a loopless topology means a topology in which each LAN can be reached from any other LAN through one path only (no loop).

• It is not possible to change the physical topology of the system, but we can create a logical topology that overlays the physical one.

Source Routing

• Another solution to prevent loops in LANs connected by bridges is source routing.

• In this method, the source of the packet defines the bridges and the LANs through which the packet should go before reaching the destination

Routers

• Routers have access to network layer addresses and contain software that enables them to determine which of several possible paths between those addresses is the best for a particular transmission.

• Routers operate in the physical, data link, and network layers of the OSI model.

• Routers relay packets among multiple interconnected networks. They route packets from one network to any of a number of potential destination networks on an internet.

Gateways

• Gateways potentially operate in all seven layers of the OSI model.

Gateways

• A gateway is a protocol converter. A router by itself transfers, accepts, and relays packets only across networks using similar protocols.

• A gateway can accept a packet formatted for one protocol (e.g. AppleTalk) and convert it to a packet for another protocol (e.g. TCP/IP).

Gateways

• A gateway is generally software installed within a router. The gateway understands the protocols used by each network linked into the router and is therefore able to translate from one to another.