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Switch after a Hub?

By kent ·
Can you have a Switch after a hub? Please explain in detail. I have been told that if you have a hub before a switch it will slow everything down.

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Switch after a Hub?

by tbradley In reply to Switch after a Hub?

You've been told correct. The difference between a hub and a switch is essentially this. Both pieces of equipment are rated at a "line speed", wether it be 10mps, 10/100, or straight 100mps. That is the theoretical limit of how much data can flow out of each port.

The hub shares it's line speed with all devices attached to the hub, so if you have a 100mps hub, with 10 devices attached, each device gets 10mps. This number is not exactly even due to how much each device is working the network, but it's a good rule of thumb.

The switch doesn't share. a 100mps switch with 10 devices attached gives each device a dedicated 100mps, regardless of what each device is requesting.

A switch attached to a hub will only use the bandwidth given to it, so you may be effectively slowing a 100mps switch down to 10mps linespeed, or less, depending on hub utilization.

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Switch after a Hub?

by mpdcsup In reply to Switch after a Hub?

Sure you can have a switch after a hub. After all, isn't that the same thing as having a hub after a switch looking at it from the other end?

To advise you properly, one would have to know how information flows between your hosts.

The amount of information that moves through a hub over an interval of time will never exceed the bandwidth of any single port.

In a switch, the amount of information that passes through is limited by the bandwidth on each port.

If all of the traffic is between a single server and a number of clients, neither the hub nor the switch would perform better.

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Switch after a Hub?

by mpdcsup In reply to Switch after a Hub?

There is a significant flaw in the explanation given in Answer 1. The division of bandwidth on a hub occurs only under full, concurrent utilization.

If the hub is rated at 100Mbps and only two devices, say Host A and Host B, are talking, thehub will give them the full bandwidth (100Mbps) -- like the switch. Unlike the switch, however, if Host C and Host D stike up a conversation, the connection between A and B will fall back to 50Mbps and C and D will establish a 50Mbps connection. The switch, in this latter case, would allow both conversations to occur (concurrently) at 100Mbps.

To see the point I made in my original Answer, look at what happens when A and B are talking and C wants to talk to A:

With a hub, the existing connection between A and B falls back to 50Mbps to enable another (50Mbps) connection. The same connection on a switch also falls back to facilitate two connections on A (50Mbps each).

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Switch after a Hub?

by e_314 In reply to Switch after a Hub?

To add to all answers, make sure you have a cross-over cable between your hub and the switch. Also, make sure you do not put domain controllers behind the hub as this may cause problems with replications and broadcasting.

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Switch after a Hub?

by kent In reply to Switch after a Hub?

This question is not quite answered. I have been told that there will be a performance decrease if using switches in a small-mid network. I am not sure of the cause, possibly delay time, but there is a debate on this.
The network is as follows: server -hub -(possible hub) - switch - (possible hub) -workstation.

All hubs are 10base while switch is 100base.

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