differences between repeaters, hubs, bridges, switches and routers

Hi, Could someone tell in detail about the differences between repeaters, hubs, bridges, switches and routers.

Regards, Karthik Balaguru

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Google for "Cisco CCNA Study material". You will find the answer to this and more. Such as 'What are broadcast domains' 'collision domains' .....etc.

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repeater - signal comes-in on one port, is regenerated (?) and sent-out the other port. operates at the physical layer

hub - a repeater with more than two ports. operates at the physical layer

bridge - a frame comes-in on one port, and resent out the other port, or not if it is a learning bridge which knows which MACs are on which side of the bridge. operates at the data-link layer.

switch - a bridge with more than two ports. operates at the data-link layer.

router - a datagram comes-in on one port, routing tables are consulted to determine on which port the datagram is sent back out. operates at the network layer.

rick jones

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Rick Jones

I haven't posted here for 2 years or more, but I taught this material at the University level for a number of years.

If you're familiar with the OSI 7 layer model, it may help you keep the differences in perspective.

  1. Repeaters and Hubs These operate on Layer 1 (Physical Layer) only. Repeaters and hubs regenerate bits received on any one port, and broadcast them out on all other ports. Hence, the repeater or hub extends the physical "span" or size of the network, but only one device (computer or router, for example) can send at a time. In the Ethernet world, a network built with only repeaters or hubs has one collision domain.

Hubs are really just multi-port repeaters. 1's and 0's in, 1's and 0's out.

  1. Bridges and Switches These operate on Layer 2 (Data Link Layer). They read the destination MAC address on each packet, and forward the packet only to the port on which the target computer or router or printer is connected. The MAC address is the hardware address, coded into each device physically on the network (whether WiFi wireless, or cabled Ethernet).

Bridges and switches automatically "learn" the location of all MAC addresses (that is, which port points toward each MAC address), and build a forwarding table that allows the function described in the previous paragraph.

Bridges were traditionally (in the 1980s and 1990s) just 2 port devices; they regenerate the 1's and 0's (just as a hub or repeater would do), but they also separate the traffic on the network into two logically separate collision domains. Hence, the LAN on each side of a 2 port bridge can be busy transmitting a packet, while the other LAN can be simultaneously sending another packet ... allowing the network to carry more traffic AND extending the distance permitted by the cabling scheme (or wireless transmission distances).

A switch was a logical development of the bridge -- multiple ports, not just 2. The number of ports can be any number, but is usually done in multiples of 12 (because of silicon chip architecture of the switching chips). A 24 port Ethernet switch can, theoretically, support 24 simultaneous transmissions.

  1. Routers Originally called "gateways" (hence, "default gateway") routers were developed to link the locations of a distributed, wide-area network together. These are Layer 3, or Network Layer devices.

Some ports are meant to connect to the local LANs (Ethernet, WiFi, etc), while other ports are meant to connect to the Wide Area Network, through telephone company connections.

Routers base their forwarding decisions on the Network, or IP, address

-- and logically determining which group of computers is where through the grouping of computers at each location into what we call a "subnet"

-- a physical network where the IP addresses share a common subnet value.

It's typical that large networks are built with some combination of hubs, switches, and routers so that traffic is manageable and so that the geographically distinct locations of a corporate network can communicate with each other, OR so that all of us can communicate over the Internet.

Good luck in your studies.

(if you want to reply directly, delete the spam and nospam parts of my email address.)

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Mr. Wheels

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