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2005/08/07 What is a Managed Switch?

© August 2005 Tony Lawrence

A managed switch allows you to control the individual ports of your switch. Features of course vary with manufacturers and models, but even the most basic will have the ability to turn the port on or off and control its link speed and duplex settings. That control is for security; it prevents someone just walking in and connecting to your lan through an unused port.

Beyond that, you might be able to specify a particular MAC address that is allowed to connect. That prevents someone from replacing machines with their own. You might be able to set login authentication, also. You may be able to designate certain ports as "high priority"; for example the ports your servers are on. Setting bandwidth limits, monitoring port traffic and of course logging are also features.

VLANS (Virtual LANS) are a popular option. This allows you to set a broadcast domain on certain ports, so that broadcast traffic isn't passed on to the other ports. This can also isolate machines from each other for security purposes.

Link aggregation ties together multiple ports, allowing two switches to be connected more than once for higher throughput between them. The switch may support Spanning Tree, which lets you have multiple paths for redundancy without having to worry about looping.

These switches may also have snmp agents that will report status to snmp monitors. Nowadays they usually have a web interface for configuration in addition to the traditional command line method. Older models might require access through a serial console, but more recent devices will have the web interface.

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Fri Jan 23 09:20:57 2009: 5236   amith

This artical is very good.. I want to know how spanning tree is used in managed switches? Can anyone answer.. please..

Fri Jan 23 12:37:06 2009: 5238   TonyLawrence

That could be an article by itself. Spanning tree simply prevents loops when you have multiple switches wired together in a way that otherwise could loop back. Do a Google search if you want to find articles that explain how it works in practice,

This site deals with small business - I seldom am working with anyone large enough to even need such things; many of my customers get by with a single switch :-)

Still, these kind of features are appearing in lower priced equipment.. I imagine it might eventually show up in the $50 units my customers are more likely to own.

Tue Nov 10 06:23:57 2009: 7510   santoshchauhan

this is a nice article but not so good for begener it's just need more clearence. thank u

Tue Nov 10 12:02:11 2009: 7511   TonyLawrence

Tell me what confuses you and I'll try to help.

Tue Feb 2 02:23:48 2010: 8021   ChadSpaltro


I've been looking for information that simply explains the difference between managed and unmanaged switches. Your article gave me a good head start. From what I've read on other sites, an unmanaged switch is really a hub, or could have some segregation built in but offers no way to program or setup how it works... is that correct?

Tue Feb 2 02:39:17 2010: 8022   TonyLawrence


No. A switch is not a hub.

On a hub, every port sees all traffic. On a switch, once it learns that a particular ip address is on port 6, that's the only place traffic (except broadcasts) for that ip goes.

Tue Feb 2 02:40:57 2010: 8023   TonyLawrence


For more on switches and hubs. see (link)

Tue Feb 2 15:25:12 2010: 8024   BigDumbDInosaur


On a hub, every port sees all traffic. On a switch, once it learns that a particular ip address is on port 6, that's the only place traffic (except broadcasts) for that ip goes.

Actually, the switch learns about MAC addresses. Although IP is the dominant system at this point in time, one could theoretically use a switch in an older Novell network where IPX is used.

Tue Feb 2 15:29:46 2010: 8025   TonyLawrence


Yes. Though for this person, I didn't want to complicate his understanding.

Fri Feb 12 18:06:33 2010: 8073   anonymous


do managed switched have the ability to push dhcp to a group of ports? we have an all static ip network here, however, we have a need for dchp in a very small way. can i do this without purchasing another router?

Fri Feb 12 18:14:41 2010: 8074   TonyLawrence


A DHCP request is a broadcast - ANY switch passes broadcasts to all ports by default.

Fri Feb 12 18:15:54 2010: 8075   TonyLawrence


But if you are asking if a managed switch has DHCP server abilities, no.

Fri Feb 12 18:27:49 2010: 8077   anonymous


thats what i was asking. thanks for the reply

Fri Feb 12 18:34:14 2010: 8079   BigDumbDinosaur


do managed switched have the ability to push dhcp to a group of ports? we have an all static ip network here, however, we have a need for dchp in a very small way. can i do this without purchasing another router?

You need either a router or a computer to respond to DHCP requests. If you have a server attached to your network it can take care of this for you. If not, an inexpensive router can do the job (3Com's office-connect series is good).

I'm hoping for your sake that you are not on a Windows peer-to-peer rig. If you are, shame on the IT person who set it up for you.

Sat May 15 06:08:03 2010: 8596   THILLAIRAJAN


Do we have 2 / 3 managed Switch??

Sat May 15 12:34:37 2010: 8597   TonyLawrence


You need to rephrase that question; I'm not sure what you are asking.

Tue Jul 17 18:20:04 2012: 11203   anonymous


Hi, I have a specific question about managed/unmanaged switches and from your post, I think you know the answer. I would appreciate if you could let me know what you think:
Assume I have a managed switch and I have programmed some of its ports, e.g., ports 1-24, by pushing some static rules to them. Now someone just comes in and connects a switch to mine through one of the ports other than 1-24. I do not want him to overhear the traffic passing through the ports 1-24. But I do not want to block all the other ports (other than 1-24) on my switch either, since I want to discover the new guy and find out whether it is a managed or an unmanaged switch. What do you think I should do? Thanks a lot in advance!

Tue Jul 17 18:27:26 2012: 11204   TonyLawrence


Managed or unmanaged, the only traffic he'd see is that going through the port he connected to (unless you specifically allowed it).

Tue Jul 17 18:56:48 2012: 11205   anonymous


But the new switch should be able to see all the rules in my switch, and I do not want that to happen. What is the fastest way for me to identify the new switch as soon as it plugs in and deny its access to my rules immediately?

Tue Jul 17 19:00:00 2012: 11206   TonyLawrence


Huh? Why would he be able to see your rules??


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