I have a Cisco SG 102-24 Switch which won't work in my network. Whenever I connect it, it will initially work and then after a couple hours the computers can't communicate internally or externally

IT Guy
IT Guy used Ask the Experts™
I have a Cisco SG 102-24 Switch which won't work in my network. Whenever I connect it, it will initially work and then after a couple hours none of the computers can communicate internally or externally.

Also, when I install this switch (to replace an older 10/100 Mbps generic network switch) I have to adjust the network speed on 6 out of the 12 computers from Auto Detect to 10 MBPs half duplex; also, the network copiers and two network copiers take over an hour until the other network computers are able to communicate or print to them.

Then, after a couple hours, none of the computers or other network devices are able to communicate with each other even though the Cisco network switch is still powered on and the port lights are flashing.

Then even if the network switch is powered down and turned back on, none of the network computers and other devices are able to communicate.

I believe that this issue is being caused by the way that the network is configured.

As you can see in the attached screenshots, the server has two network adapters.

The Internal network adapter is set up to communicate on the internal network.

The external network adapter is set up to communicate with the outside internet.

The network cable that connects the company's DSL modem to the rest of the network plugs right into one of the ports on the network switch using a standard straight through network cable. This is the way that the network is configured using the existing DLink network switch. With this network switch, all of the computers and network devices communicate just fine and without any problems.

However, whenever the new Cisco SG 102-24 Switch is installed in place of the DLink network switch is when I have to make the initial changes mentioned above. And then a couple hours later all network communications cease to exist, even though this network switch is powered off, left powered off for 10 or more minutes and then powered back on.

Like I have mentioned, I have used this same network Cisco SG 102-24 Switch on my home network (which has 4 Windows 7 computers and two Windows XP laptops) and have connected the network cable from my home's cable modem directly into one of the ports on this Cisco SG 102-24 Switch and everything works fine. I have tried this network switch at home for over a week in this manner, and never have had to reboot it.

This Cisco SG 102-24 Switch is completely plug and play and cannot be programmed in any way.

Initially we had received one of these Cisco SG 102-24 Switches brand new and then had it replaced with another brand new Cisco SG 102-24 Switch, but we continued having this same issue.

I believe that the root cause of this issue has to do with this company's network configuration where it used one network adapter to communicate internally and the other network adapter is configured to communicate externally (with the internet). I contacted this company's ISP and they told me that this current configuration is the only way that their network can be configured so that the computers can communicate with the internet.

What can I do to fix this issue?
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Cisco has a little quirk on it>

If you configure the router or any other switches as autodetect, while another is 100Mb Full duplex or something else, you would think these two would talk with one another.

With Cisco, your duplex settings have to be the EXACT same. So, either auto on all or 100Mb/full duplex...

Otherwise, Intermittent communications happens.

Furthermore, ON ACCESS PORTS, and not the trunk ports, see if you have spanning tree enabled. XP and newer require portfast because spanning tree has about a 45 second hold down timer to ensure there are no L2 loops in the network. spanning tree disconnects the second link to the switch. This is the main reason I never recommend multihoming and strongly recommend ONE connection to each computer or server.
IT GuyNetwork Engineer


How do I find out if spanning tree is enabled?

I would prefer to have only one network cable connected to the server, which then runs to the (Cisco) network switch.

If any of the network traffic needs to be routed to the internet, then the (Cisco) network switch should simply forward these requests to the DSL modem, which will then forward these requests to the internet.

Please provide me with some assistance on how to set up this configuration.
IT GuyNetwork Engineer



First of all, the Static IP address (on the Windows Server 2003 for Small Business Server( for the External Network Adapter is different than the Default Gateway address-I had to hide this information since it is a unique public IP address.

The D-Link is a network switch. The DHCP is handled by the Windows Server 2003 for Small Business Server.

Both of the network cables that plug into the two network ports on this server connect directly to the DLink switch. The DSL modem also connects directly into this same DLInk switch with a Category 5 network cable.

I am an IT consultant who has been called in to help streamline and improve the operations and settings for this network.
On a "smart switch"  you will probably not have a way to interface with it to see if spanning tree is enabled. On Cisco, type the Comman line or web interface should show you if you are using spanning tree on the switches.
IT GuyNetwork Engineer


Great explanations.

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