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I recently added a Netgear GS108T Managed Switch into my network setup. I previously had a Netgear GS108 unmanaged Switch in the spot the managed switch is at now. I plan to team a couple nics on at least one PC and on the Netgear ReadyNAS Pro Business hence the need for a managed switch.

As long as I have PC>switch>Router/Firewall>Cable Modem it doesn't matter whether it is the GS108 or the GS108T everything seems to work fine. However PC>GS108T>GS108>Router/Firewall>Cable Modem introduces incredible lag. Is there an inherent flaw in hooking a managed switch into an unmanaged switch?

I have more PDa's, Smartphones, notebooks and PCS not diagrammed as they are currently offline until I get the basics worked out with these devices.

RCA DCM425 CABLE MODEM>SecureComputing/Snaggear SG570>Netgear GS108 unmanaged Switch>Netgear GS108T Managed Switch>PC 
RCA DCM425 CABLE MODEM>SecureComputing/Snaggear SG570>Netgear GS108 unmanaged Switch>PC fine
RCA DCM425 CABLE MODEM>SecureComputing/Snaggear SG570>Netgear GS108T Managed Switch>PC fine 

Example of a PC's static IP setup

IP Address:
Subnet Mask:
Default gateway:
Preferred DNS server:

Setup of the managed switch

IP Address:
Subnet Mask:
Default gateway:

Here is a Visio layout of my current setup:

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What happens if you swap the positions of the gs108t & the gs108? – jftuga Jan 22 '11 at 5:01
I hope the IP addresses you are using are only examples and not the real ones in use. RFC 1918 has defined a number of blocks for private use: 10/8, 172.16/12, 192.168/16. – toppledwagon Jan 22 '11 at 6:12

There isn't anything which should obviously fail to make this work. However there are always edge cases and varying gotchas.

For example, your managed switch might be trying to go into full duplex mode, while the un-managed switch is in half-duplex mode. This would cause a lot of packets to get viewed by the unmanaged switch as a collision, resulting in extremely poor throughput. (This specific example is highly unlikely with Gb throughout as it is full-duplex in the spec.)

What you want to do is dig into your managed switch and look at the configuration and counters for the ports involved in the traffic flow. Make sure that the switch port is in sensible settings, and isn't accumulating errors. If the switch has logging capability, crank it up; send it to a syslog server if the switch is so-capable (and you have a syslog server).

Check the error counters on the attached devices too, that might tell you what is going on.

If there is something wrong, frequently the switch will tell you what it is, or give you a hint that will help you figure it out.

Also, you might sniff the traffic going into the affected computer with Wireshark or something, you might get some hints that way.

(And just off the top of my head while banging this all in, I wonder if your switch-to-switch connection has enabled jumbo frames and that might be what's causing your issue.)

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Beat me to it! =) – Wesley Jan 22 '11 at 2:31

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