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difference between router & switch

Posted on 2002-05-23
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what is difference between router & switch?

i bought a device to share broadband. It is connected to the cable modem and the LAN card of my PCs


I don't know whether it is called a switch or a router
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Question by:CYBERWORLD
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9 Comments
 
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by:
mschech earned 200 total points
ID: 7029738
it is probably a router.

A switch directs data based on the physical
ethernet hardware address.
(like 000EC324A230)

A router directs data based on the IP number.
(like 192.168.123.1)

A cable router typically has the ability to
give out IP addresses to multiple computers on a LAN.

The cable companies set up the cable modem so it only
talks to one MAC address (physical ethernet card)
The cable modem sees the router's address as it's
single PC. The cable company's DHCP server then assignes
the router a IP address (such as 66.24.191.23).

On the other side of the router, the router's DHCP
assigns each of your computers an IP number in the
private/test range of 192.168.123.1-254. It would typicall
show up on your LAN as 192.168.123.255 as a "gateway"

When your PC attempts to get to a website, it
(at 192.168.123.2, say) sends a request to it's
"gateway" which is the router (at 192.168.123.255)
The router then passes the request to it's upstream side,
and sends it out to teh cable modem.
The cable modem (and the world) sees the request coming
from the router (at 66.24.191.23, which is what the
cable company expects to see.

The router keeps track of which data packets and ports are responses
to other ones so each of your computers get the right data.



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Expert Comment

by:gavrc
ID: 7029846
The device could even be a hub. The cable modem is doing all the 'routing' work, device sharing can be simple ethernet. Does it have any ID markings on it  manufacturer/model/FCC number?

BTW. More expensive level 3 switches can direct packets by IP and in effect function as routers. In heavy traffic situations switching is faster as the destination MAC is advertised on the outside of the packet, the packet needs to be opened to see the destination IP. Routing comes into it's own in subnet situations where traffic needs to be seperated between groups of machines to minimise unnecessary traffic over a smaller link.
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by:lrmoore
ID: 7029914
Most of the low-end cable/dsl devices are a combination router and switch in that you have an uplink (WAN) port that actually gets the IP address from the provider and typically "masks" those workstations that are on the LAN side. If there is more than one LAN port, i.e. 4-ports, then these are switch ports. A switch connects all ports into a layer 2 broadcast domain that does not care what protocols run over it. The router part takes the layer 3 (IP addresses) and translates/routes based on source/destination addresses between the WAN port and all LAN ports.
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Expert Comment

by:stevenlewis
ID: 7030952
I go with lrmoore. I have a d-link DI 704P
it is both a router and switch, the router for the lan to wan connection and the switch for the lan
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Author Comment

by:CYBERWORLD
ID: 7031010
it is true that a pure switch does not have WAN port but only LAN port?
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Expert Comment

by:stevenlewis
ID: 7031034
a switch is just a smarter hub. It "learns" which ip addresses are connected to it's ports and sends the data to that port, thereby cutting down on network traffic. It will not route between networks
it is true that a pure switch does not have WAN port but only LAN port
yes
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Author Comment

by:CYBERWORLD
ID: 7031059
Thanks all...

i think lrmoore and steven are right. My device should be a route + switch

but mschect's illistration of a router is good.... thanks
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Expert Comment

by:mschech
ID: 7031807
yes, they are right.
What is commonly called a "cable router"
is usually a router,switch, and what we all forgot to mention, a firewall, in one box.

Most of them come pre-setup so any windows PCs
on your LAN side will be protected from the cable side.
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Expert Comment

by:rmreed
ID: 8294017

 Q: What is the difference between a Hub, Switch, and Router (#5456)  
 A: Hubs operate at ISO layer 1 - physical layer, Switches operates at ISO layer 2 - data link layer, and Routers operate at ISO layer 3 - network layer.


HUB When Ethernet was originally designed it used a single fat coax called a backbone. Individual hosts were physically connected to the backbone. This created a party line. Each host has to listen for the backbone to be idle before it started talking. It is possible more then one host will start talking at the same time, in that case the messages collide making them unintelligible. This condition is detected each transmitter stops talking and waits a variable interval before attempting to talk again. The Ethernet network is called a collision domain, since all devices must wait until the line is clear, and may inadvertently interfere with one another.

When Ethernet was modified to run over Unshielded Twisted Pair (UTP) Category rated wiring the original coax backbone was shrunk within the hub, called a collapsed backbone. Functionally a hub operates exactly as the old coax backbone. The ports on the hub provide a point-to-point connection to the Ethernet interface in each computer. With a hub each node must wait for the network to be idle and detect collisions between multiple nodes.

SWITCH As Ethernet networks grew in speed and size the party line nature was recognized as a performance limitation. Switches eliminate the collision domain and work much like the telephone switching system.

When an Ethernet packet arrives at the switch the destination MAC address is examined and the packet is switched to the proper port. Each Ethernet interface has a Media Access Controller (MAC) 48-bit address assigned by the hardware vendor. The switch remembers which MAC addresses are connected to each port. If the Switch does not know which port to use it floods the packet to all ports. When it gets a response it updates its internal MAC address table.

This means Port A can talk to C at the same time F is taking to B. This greatly increases overall performance even though it does not change the speed of individual connections. Because the collision domain is eliminated connections are able to use full duplex, hosts can transmit and receive at the same time improving performance even more.

ROUTER A router is used to interconnect multiple networks. The Internet is literally Internetwork -- a network of networks. Internet router’s work on IP addresses to determine how best to interconnect the sender to the destination. Because router’s work at the IP layer different physical networks can be interconnected, Ethernet, Token Ring, Sonet, even RS232 serial used for dialup can carry IP packets.

Routers intended for home use include Network Address Translation (NAT). This allows a single address assigned by the ISP to be shared by multiple hosts connected to the local network.
 
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