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Ethernet Switch and DHCP

Last response: in Networking
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February 7, 2013 6:50:43 PM

I have a custom built computer, which we will call X, and an IBM ThinkCentre which are both connected to a Allied Telesyn fast Ethernet switch. The switch is connected directly to port one of a Comcast wireless router, port two and three being connected to a family computer and a small Dell desktop server, respectively.

The problem I have lies in the switch and X. When X and the IBM are both plugged in to the switch, a mysterious thing happens. If the IBM is on and plugged in to the switch without X, it receives network status and Internet access. If X is turned off and then plugged into the switch, the IBM continues to receive network status. If X is then turned on, all is normal. However, when X is then turned off while connected to the router, the IBM and any other device plugged into the router loses network status (appears as offline in the router). Furthermore, when X is unplugged from the router, on or off, all other devices on the switch regain (or continue to have, if applicable) network status and appear in the router's settings as online once again. I can set a static IP for the IBM on the router and then go into the network card IPv4 settings to set that up on the machine, and then there's no problem. However it's a great hassle as our computers are often taken to other locations and need the ability to use multiple IP addresses. Also, it's worth noting that X will always connect to the network, IBM or not.

I've posted about this twice on StackExchange's Super User site and received ideas along the lines of X providing DHCP addresses, which it's not. It's not set up to, one, and the IP address is coming from the router as X can be unplugged when a new device is added and the router will communicate. Another idea was that I was using a media converter. I don't know what that is, or how it functions, but I do know I don't have one. Someone else said ICS (Internet Connection Sharing), which is only enabled if you have multiple network interfaces on one system.

Both computers are using Windows 8 Professional, X being 64-bit and the IBM being 32-bit.

Thoughts? It's a persistent problem and I hate it.

More about : ethernet switch dhcp

February 7, 2013 7:59:12 PM

If your router has dynamic address reservation, assign the MAC address of the IBM a reserved address. It is very similar to a static address, but the computer still is set to automatically obtain an IP address and it may maintain the connection.
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February 8, 2013 1:27:24 AM

RealBeast said:
If your router has dynamic address reservation, assign the MAC address of the IBM a reserved address. It is very similar to a static address, but the computer still is set to automatically obtain an IP address and it may maintain the connection.


The model of the router is SMCD3GNV. Don't know if that tells you anything, but when I looked into the router I couldn't find anything relative to dynamic address reservation. In the advanced settings there are Port Forwarding, Port Triggering, DMZ, Dynamic DNS, and Device Discovery.
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February 8, 2013 12:40:53 PM

Yeah, I looked up the manual and unfortunately it is a very basic gateway that lacks dynamic reservation.
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February 8, 2013 6:07:37 PM

Are you using a crossover cable to connect the switch and X?
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February 8, 2013 7:14:22 PM

TheMan007 said:
Are you using a crossover cable to connect the switch and X?
Not likely an issue since X is very likely to have a gigabit connection, hence auto-MDIX. If he used a crossover and didn't have gigabit it wouldn't connect.
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February 8, 2013 8:08:37 PM

Just a wonder. I know when we used to do labs in class, we'd use the eagle server connection with a crossover, even with the switch plugged into a router, it automatically tried to hit the eagle server as a DHCP versus hitting the router.
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February 10, 2013 12:53:42 AM

X has a Qualcomm Atheros AR8161 PCI-E Gigabit Ethernet Controller (NDIS 6.30) according to Device Manager. I know it's an integrated card.
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February 10, 2013 3:14:16 AM

Is X running any sort of Internet Connection Sharing? Perhaps X is providing DHCP for your other devices somehow? If you were talking about a modern Linux OS I would have you..

chkconfig --list | grep dhcp

To see if you are acting as a DHCP service running either as a client or server.

What happens when you configure the hosts statically?
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February 10, 2013 3:33:00 AM

dbhosttexas said:
Is X running any sort of Internet Connection Sharing? Perhaps X is providing DHCP for your other devices somehow? If you were talking about a modern Linux OS I would have you..

chkconfig --list | grep dhcp

To see if you are acting as a DHCP service running either as a client or server.

What happens when you configure the hosts statically?


X is running Windows 8 Pro x64 with only an Ethernet adapter, so ICS is out completely. What do you mean by "configure statically"?
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February 11, 2013 2:51:13 PM

Not sure about Windows 8, but ICS could, and often was enabled on earlier versions of Windows... Modem support and all you know... Might be worth checking.

By configure statically, I mean to assign your machines their IP configurations manually, don't let DHCP do it for you.
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February 11, 2013 3:04:21 PM

I don't know what to say. It appeared to have just fixed itself.
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