Resetting cable modem?

I have a Motorola SB5100 modem which I use with 2 computers. I use a KVM switch and a Cat5e RJ45 switch. The problem is when I switch the modem between computers I have to power off the modem manually to allow it to reset. Is there any way to avoid that?

I was wondering if the modem could be connected to both running computers at the same time, using a Y connector, and avoid the powering off annoyance.

Is there a better way to do this, or isn't it possible?

The closest thing to a Y connector for Ethernet would be a hub or a switch. (Note that a "switch" doesn't refer to a physical connection that turns on and off, but rather to a method of only sending packets to the leg of the switch that is concerned with them. A hub simply broadcasts all packets to all legs.) But for that to work, you would need to contact your cable ISP, and pay for two IP addresses. (Assuming your cable company even offers this option.)

The easiest way to handle this situation is to get a home broadband router, connect the router to the cablemodem, and connect the computers to the router. In this situation, the router gets an IP address assigned to it by your ISP's DHCP server. The computers connected to the router get private range IP addresses from the router. NAT (network address translation) is used to direct packets only along the proper route.

Just buy a cheap router and you can use both computers at the same time without this hassle. They (routers) are available for as little as $25. Probably less than you paid for the switches.

Try releasing dhcp before switching and then restarting after.

However, a better way, is to buy one of those cheap firewall/router boxes, which will not only eliminate that problem, but also greatly improve security.

I was reading today that the SB5100 may occasionally need to run a power cycle or some such. I don't remember why, but it was basically a re-boot. The article said that cutting the power for 2 minutes did the same thing. I also have the SB5100 but am using a Linksys switch and have 4 computers on the internet at the same time through the switch. I have only had high speed for a couple of weeks and can only network the 4 by disconnecting the SB5100 and assigning each a static IP address. You shouldn't need a Y connector at all. In fact you can run both the USB and the RJ45 off the back at the same time. Does your KVM switch not like your SB5100? Have you tried running winipcfg from start> run> winipcfg>

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Multiple IPs will likely be on the same subnet. This will cause the computers to send the packets directly to the other computer, using it's MAC address, and not through the ISP.

A power-cycle *is* cutting the power. The length of time doesn't usually need to be 2 minutes. Just long enough for the CMTS to realize that the cablemodem is no longer there. Thirty to sixty seconds should be long enough, but since most people are pretty bad at estimating that length of time, saying 2 minutes usually will get them to sit still for 30 seconds.

As for the need to do a power-cycle, it's not just something that the SB5100 needs. There are reasons to power-cycle *any* cablemodem. Switching the device connected to it is one reason. Wanting to start with a clean-slate for troubleshooting is another.

Dump the switch, and get a router.

With the switch, each computer is assigned it's own public IP address by the CMTS. Communication between the machines while they're connected to the Internet is through the CMTS. That's the route that all packets will follow. The packets will go right past the switch, straight to the Internet. To get back, they need to be turned around out there, and sent back. However, the ports they use are likely blocked as a security measure. Otherwise you could get into any of your neighbor's machines if they have file and printer sharing turned on.

You could get around this by using a protocol other than TCP/IP. One that won't pass the switch. But it would just be easier to replace the switch with a router instead of running multiple protocols.

Only if he's paying for multiple IP addresses, and the firmware sent by the cablecompany hasn't disabled the use of both ports at the same time. He would also have to install a driver on the machine using the USB connection. And there are quite a few good reasons to avoid USB networking, especially when an Ethernet NIC is available, and a router can be used.

KVM stands for Keyboard, Video, Mouse. It has nothing to do with his Ethernet connection.

You can't use a Y connector with Ethernet. It doesn't work that way. And when speaking of a switch in Ethernet terms, it is not a device that physically connects or disconnects a connection like an AB or KVM switch. With an Ethernet switch, all the ports are active at all times. Switching refers to what the packets do when they get to the switch.

He's still going to need the KVM switch, unless he gets a second keyboard, a second vidoe monitor, and a second mouse. The KVM switch allows him to need only one of each, and still be able to control two computers.

I can't remember the last time I saw someone with multiple IP's on the same subnet. It may happen, but it happens far less than IP's on different subnets. And based on the poster I was replying to, this is most likely the case for his multiple IP's as well.

Basically yes but it is quite a bit more complicated in a DOCSIS environment. The cablemodems (at least the two I've seen from close) usually try to "pull" traffic to themselves by answering to ARP requests at least for PCs they don't allow internet connectivity due to reached CPE value. This is being done because the IP range is used within the local subnet of the cable system and if your PC tries to contact your neighbour's PC, the data need to be transmitted over the cablesystem to the CMTS and back to the neighbour. Direct communication is not possible because upstream and downstream frequencies and coding are different and there generally is encryption on the cable system, so everything needs to make an u-turn at the CMTS.

Since the IP range is however the same for all PCs and they all think it is but a normal ethernet, the cablemodem must answer some of the arp packets in other systems stead to draw the traffic to itself in order to send it to the CMTS.

Now I'm not sure what exactly is supposed to happen if you connect 2 PCs to the same cablemodem and try to transfer data between them. But I have seen occasions of a race condition where both the receiving PC and the cablemodem answered the ARP request. Sometimes the data then was sent directly to the receiving PC and other times the cablemodem won and all the data went to the CMTS just to loop back again (with resulting speed limit)

Of course having a router solves the problem but you can also create static arp entries in your PCs if that happens.

However, I believe the original poster's problem was simply that he reached the MaxCPE value of his cablemodem and if he switches PCs, he needs to powercycle it in order to reset the list. There's nothing around that, except MAC cloning (or buying a router)

CU

Rene