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How come network sniffing software can work over a switch?

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http://serverfault.com – We have several of standard non-managed 3com switches in a network. I thought switches were supposed to only send packages between peers of a connection. However it appears network sniffing software running on a computer attached to one any one of the switches is able to detect traffic (ie youtube video streaming, web pages) of other host computers attached to other switches on the network. Is this even possible or is the network thoroughly broken? Thanks. (HowTos)

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Submitted by taskli on 01/01/2012 – Made popular on 01/01/2012

Stories similar to How come network sniffing software can work over a switch?

I have a office network with approx 150 devices (computers/printers/ip phones). Almost all of the end point devices have straight run Cat5e from my Hp switches directly to the device. IP phones for each end user sit between the hp switch and computer.

We have 3 different types of switches in our network.

All of our IP Phones are running on HP 2520-24 PoE switches. Our primary backbone is "supposed to be" running on Netgear GS748T switches. Our OLD switches are Dell PowerConnect 2848. These need to be removed.

I've drawn two diagrams (below).

Network Structure 15 weeks 1 day ago

Can you please help me understand when it makes sense to move to a network structure with a managed core switch and managed access level switches. Currently, our network is made up of all unmanaged switches (8 of them) that are either home run back to one main switch or in the case of our factory floor network, the switches are daisy chained together and then feed back to the main switch.

I have 6 Juniper switches (EX - 2200) connected to each other as shown in the network topology.

I have two PC's that I am using

PC1 - (used for configuring the 6 switches via minicom)

PC2 - to monitor the traffic between the switches via the Ports that are marked with arrows in the diagram.

STEP 1:

I create a new vlan On Switch 3 (SW3) that includes Port 12 and Port 22.

I have 6 Juniper switches (EX - 2200) connected to each other as shown in the network topology below. I have two PC's that I am using

PC1 - (used for configuring the 6 switches via minicom) PC2 - to monitor the traffic between the switches via the Ports that are marked with arrows in the diagram.

STEP 1:

I create a new vlan On Switch 3 (SW3) that includes Port 12 and Port 22. I also assign l3-

I am trying to set up a connection between 2 buildings. In building 1 I have the following:

Network 1 192.168.2.0/24 Network 2 192.168.3.0/24 Network 3 192.168.0.0/24 Network 4 192.168.180.0/22

All the above are just different subnets on different cables. Let's say I run one cable to building 2.

I don't know a lot about network switches. I was wondering if one would help speed up a network with three computers, a wii/netflix as the main internet connected devices? Would it be worth it to purchase one? And, yes, I do have slow upload speed to my server and the connection is in and out a lot. Would a switch be helpful?

We have a scenario where we have 60 computers that need to be loaded with Windows7 at our company as well as have all windows updates installed. Our company has an internet especially for visitors and since these computers are for a client the contract states they are never to be connected to our own companys network. Therefore, they must be installed on the visitor side of our network.

we're sharing a server room with another company, including the network infrastructure. All the switches are HP ProCurve, in various models depending on port need and so on.