Hub versus switch

Experts,

Given a hub with five computers connected to it. One computer broadcasts
and all others hear it. Now, given a switch with five computers connected
to it. One computer broadcasts. Do all others hear it? Why or why not?

 

In

A switch is an OSI Layer 2 device (based on the MAC address). The higher you
go up the OSI model, the more intelligent the device is that works on that
layer. For example, a router is a Layer 3 device (the Network Layer where IP
lives).

Therefore, being intelligent enough to be aware of the MAC addresses, a
switch builds a "routing" table based on MAC addresses it is aware of when a
device is plugged into a port, but not IPs, since it's on the wrong layer.
HOwever at times, I don't usually like to use the word 'routing' in this
definition because it can be confused with a router, so we should look at it
as a 'destination lookup table' that keeps track of each port and the MAC
sitting on it. Some switches, like the Ciscos, can build a table with about
40,000 entries, if I remember correctly, and has a propeitary shared memory
pool that is able to transfer data independently between ports more
efficiently than other brands. Others don't do as well. Yes, you do get what
you pay for. Anyway, a switch will look at the source MAC and the
destination MAC in the packet. If the destination is a broadcast, make it
so. If it's directed transmission, say from a machine with a MAC address of
MAC1 on port 32 to a machine with a MAC address of MAC5 on port 15, then the
trafffic directed from only port 32 to port 15 and no others will 'hear' or
'see' that traffic.

Hubs are just repeaters that repeats traffic on all ports and have no
intelligence... cheapos now days.

btw- There are Layer 3 switches too. They are switches that you can define
each port to be 'switched' or routed, such as an IP router. They are of
course more expensive. I believe the Catalyst 2850 are Layer 3 switches,
where we can create IP subnet VLANs.

The higher you go up the OSI, the more intelligent, and the more expensive
the device is.

Hope that helps.

--
Ace

This posting is provided "AS-IS" with no warranties or guarantees and
confers no rights.

Having difficulty reading or finding responses to your post?
Instead of the website you're using, I suggest to use OEx (Outlook Express
or any other newsreader), and configure a news account, pointing to
news.microsoft.com. This is a direct link to the Microsoft Public
Newsgroups. It is FREE and requires NO ISP's Usenet account. OEx allows you
to easily find, track threads, cross-post, sort by date, poster's name,
watched threads or subject.

Not sure how? It's easy:
How to Configure OEx for Internet News
http://support.microsoft.com/?id=171164

Ace Fekay, MCSE 2003 & 2000, MCSA 2003 & 2000, MCSE+I, MCT, MVP
Microsoft MVP - Windows Server Directory Services
Microsoft Certified Trainer
Assimilation Imminent. Resistance is Futile.
Infinite Diversities in Infinite Combinations.

The only thing in life is change. Anything less is a blackhole consuming
unnecessary energy.
===========================

 

Yes.

The Ethernet standard states device share the eletrical bus between them. A
tool known as CSMA/CD is an arbitrator determining who has access to the
network at the moment. Since only one device can transmit at a time, each
machine must wait in turn before they can send a packet. If two devices were
to send a packet and an eletrical collision was to occur, the sending devices
would sense the collision and retransmit their data. A hub can be seen as a
tool that shares the bus. It allows multiple devices to operate on the same
bus within the limits of CSMA/CD.

A switch extends the power of a network by electrically isolating each port
on the switch thereby eliminating the need for CSMA/CD in a sense (still
necessary if you hosts attached to a hub which is attached to a switch). The
only two devices operating on the wire are the sender and the receiver. This
allows you to configure data transmission to occur in a full duplex manner
allowing you to achieve double the original throughput. Plus you no longer
have to wait your turn. The drawback is that the switch must analyze the
packet- slowing down the overall speed of a network. Today though most
switches operate more efficiently then hubs with more than four attached
devices.


Layer 3 (routers and layer 3 switches- VLANs) devices will help to elimate
broadcasts.
Hope this helps.

alex k
alex k

 

Yes.
Switches are Layer2,..they stop "collisions" not broadcasts.
Broadcasts are stopped by Layer3 devices (routers).

--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
-----------------------------------------------------
Understanding the ISA 2004 Access Rule Processing
http://www.isaserver.org/articles/ISA2004_AccessRules.html

Microsoft Internet Security & Acceleration Server: Guidance
http://www.microsoft.com/isaserver/techinfo/Guidance/2004.asp
http://www.microsoft.com/isaserver/techinfo/Guidance/2000.asp

Microsoft Internet Security & Acceleration Server: Partners
http://www.microsoft.com/isaserver/partners/default.asp

Deployment Guidelines for ISA Server 2004 Enterprise Edition
http://www.microsoft.com/technet/prodtechnol/isa/2004/deploy/dgisaserver.mspx
-----------------------------------------------------