albert.remo Fri, 01/26/2007 - 00:23
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Good Day! Here is a basic comparison between a switch and a bridge.


Filtering Decisions - Software based

STP - Single instance

No. of Ports - More

Forwards Layer 2 Broadcast - Yes


Filtering Decisions - hardware based (ASIC chips)

STP - Multiple instances

No. of Ports - Less

Forwards Layer 2 Broadcast - Yes

Learning MAC address -Both examines source address of each frame received

Forwarding Decision -Both are based on layer 2 addresses




mahmoodmkl Fri, 01/26/2007 - 23:16
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Just to point out the bridge will have less ports compared to switch.



johnmar.mulder-... Sat, 01/27/2007 - 00:02
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As wqs said:

A bridge USUALLY has less ports then a switch (but not always)

All the details said above are true, but might be lacking the mention of the (obvious) outcome of one:

Hardware vs software

Bridge is software based switching

Switch is hardware based switching

This means that briges are not as fast as switches.

(If this helps, please rate)

scottmac Sat, 01/27/2007 - 06:05
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In basic operation, a switch *IS* a bridge.

They both break up collision domains, operate at layer two, build their forwarding tables the same way ....

Where the definations start to diverge is in higher functionality.

Switches originally were promoted to be (virtual) "bandwidth multipliers"; a HUB uses shared bandwidth / collision domain ... exactly ONE host could talk at any given time (sucessfully ... two or more caused a collision).

When switches were introduced (Kalpana, later bought by Cisco) their big selling point was that multiple pairs of hosts could talk at the same time, each pair on its own collision domain / circuit / bandwidth, with the general effect being that instead of 10 Mbps of bandwidth shared by all hosts (on a HUB), you could now support (total ports / 2 * 10Mbps) of bandwidth (on a switch).

Additional functionality was added later; things like broadcast control, multicast control, VLANs, multi-instance Spanning-Tree (some switches still only support one STP instance), VTP (Cisco proprietary), etc.

For the sake of general discussion these days, you will usually see "bridges" used to convert the media (i.e., fiber-copper, Ethernet - Serial, and, for the old timers, Translational Bridges ... Ethernet - Token Ring) and switches used for connecting collections of hosts.

Again, pretty much anything you can say about how a bridge operates at a basic level can be said about a switch (breaks collision domains, propagates broadcast/multicasts, Layer 2 device ...).

Bridges these days will tend to have only a few interfaces, and are likely to have special functionality (like a wireless bridge).

Switches are also the only realistic way to provide full-duplex operation on Ethernet. Hubs cannot support half-duplex.

It's better to not really talk about bridges as a device, but as a function. You can turn any Cisco router into a bridge with a couple commands.

So, to directly answer your question: at the level of basic operation, there is NO difference between a switch and a bridge.

Above the "basic operation" level, the multiplication of potential caveats (vendor, generation, purpose, price range ...) makes it, at best, very difficult to describe all the possible differences in the space provided.

Hope this helps ...

Good Luck



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