New cable modem causing havok

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New cable modem causing havok

Postby pittsoccer33 on Fri Apr 11, 2014 9:07 am

After Comcast raised their modem rental fee I bought my own Motorola to replace it.

Something screwy is happening on my pc that is hard wired to my router. I often get web page timeouts. Its random, but sites as common as google.com often fail to load.

I thought it might be my DNS, so I've tried several things - flushing it, disabling the cache, and setting my router to use Google's instead of Comcast's. Nothing works.

What does work? My netbook connected over wifi. When my PC is timing out on a web page the netbook has zero trouble opening the same page.

Help :(
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Re: New cable modem causing havok

Postby mac5155 on Fri Apr 11, 2014 9:14 am

First thought is the Ethernet cable. Your new modem might require a crossover Ethernet cable. If that's not the case, check the TCP/IP settings on your PC. I don't think that would change anything - but, make sure you're obtaining an IP automatically. The DHCP might not be handing out IPs properly.
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Re: New cable modem causing havok

Postby shmenguin on Fri Apr 11, 2014 9:23 am

can you ping the same website when you're getting timeouts?
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Re: New cable modem causing havok

Postby pittsoccer33 on Fri Apr 11, 2014 9:23 am

mac5155 wrote:First thought is the Ethernet cable. Your new modem might require a crossover Ethernet cable.

Thats interesting. I didn't use the cable in the box, just the one I already had in place. So I will try that. I'd think that would be an all or nothing problem though, no?

mac5155 wrote:If that's not the case, check the TCP/IP settings on your PC. I don't think that would change anything - but, make sure you're obtaining an IP automatically. The DHCP might not be handing out IPs properly


I never set up a static ip on that computer, but it seemed to me that the port on my router determined the first few ip addresses. Regardless I will check it - I need my PC to be static so I can access my Plex server.
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Re: New cable modem causing havok

Postby pittsoccer33 on Fri Apr 11, 2014 9:24 am

shmenguin wrote:can you ping the same website when you're getting timeouts?


Never tried it but I will investigate how to do this and give it a whirl. What would being able to, or not able to, tell me?
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Re: New cable modem causing havok

Postby shmenguin on Fri Apr 11, 2014 9:35 am

pittsoccer33 wrote:
shmenguin wrote:can you ping the same website when you're getting timeouts?


Never tried it but I will investigate how to do this and give it a whirl. What would being able to, or not able to, tell me?


run the command prompt and enter:

ping google.com

if you get a timeout there or some other error, then you know it's a total connection failure. it's not super helpful, but it's a start.
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Re: New cable modem causing havok

Postby mac5155 on Fri Apr 11, 2014 9:46 am

pittsoccer33 wrote:
mac5155 wrote:First thought is the Ethernet cable. Your new modem might require a crossover Ethernet cable.

Thats interesting. I didn't use the cable in the box, just the one I already had in place. So I will try that. I'd think that would be an all or nothing problem though, no?

mac5155 wrote:If that's not the case, check the TCP/IP settings on your PC. I don't think that would change anything - but, make sure you're obtaining an IP automatically. The DHCP might not be handing out IPs properly


I never set up a static ip on that computer, but it seemed to me that the port on my router determined the first few ip addresses. Regardless I will check it - I need my PC to be static so I can access my Plex server.


Yes, I too would think it'd be all or nothing.. but it's a shot.
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Re: New cable modem causing havok

Postby ffemtreed on Fri Apr 11, 2014 9:51 am

Give me your exact setup and equipment. More specificly is your router built into the cable modem or do you have a separate router.
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Re: New cable modem causing havok

Postby pittsoccer33 on Fri Apr 11, 2014 10:03 am

ffemtreed wrote:Give me your exact setup and equipment. More specificly is your router built into the cable modem or do you have a separate router.


Image

The router is a Belkin F5D8236-4 (I think). It could potentially be on the fritz - its a 2009 model I've used since then.

The modem is a Motorola SB6121

The switch (which should have nothing to do with this) is a cheap unmanaged D-Link 4 or 5 port.
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Re: New cable modem causing havok

Postby shmenguin on Fri Apr 11, 2014 10:09 am

you have a router, a modem and a switch?

are you plugging into the switch or the router, currently?

when you plug into the other one, do you still get connection problems? can you plug into the modem directly and see what happens there?
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Re: New cable modem causing havok

Postby pittsoccer33 on Fri Apr 11, 2014 10:13 am

pc is plugged into the router. I just labeled it router/switch for kicks. the actual switch is for some gear in my bedroom.

i will try plugging directly into the modem tonight to see what happens there. not sure why that didnt occur to me.
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Re: New cable modem causing havok

Postby mac5155 on Fri Apr 11, 2014 10:38 am

Admittedly my experience is more with RF devices than the networking side but I'm thinking it wont hurt to clear your ARP table as well.

http://www.techrepublic.com/blog/window ... windows-7/

This basically links your computer with the outside world. Im wondering if somehow the MAC of the old modem is stored in your PC somewhere.

Also a power cycle on the modem and make sure the first thing that you connect to it is the router. Some ISPs will only allow one MAC address to be in their DHCP I believe. Again, I'm not entirely familiar with signals etc. once they leave the walls of a building.
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Re: New cable modem causing havok

Postby ffemtreed on Fri Apr 11, 2014 10:45 am

Ok here is what I would do. Break it down to simple components and add back on till you find the problem.

Start with just the modem hooked to the router (make sure you go into the WAN port on the router). Setup the Router to work with Comcast suggested settings (personally I would stick with openDNS or GoogleDNS) Make sure DHCP setup on the router is setup to give the correct DNS server you want to use.

Set all your clients up to use DHCP to get their IP address and network settings.

There is really nothing you can mess up in your scenario. If the clients work over WIFI then all the wired should work as well. If something wired isn't working its more than likely a problem with that individual device rather than your setup. As long as you got the cable modem plugged into the WAN port everything should pretty much just work.

if you have been playing with your router, it might help to reset it back to factory default and start over.

Oh yeah, that extra switch you have, is it a router/ switch??? If so make sure you don't plug anything into the WAN port on the extra switch. It should autosense and correct itself, but in theory you should use a cross-over cable to connect two switches together. But in reality almost anything made in the past 10 years is going to auto correct, so I really wouldn't worry about it.
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Re: New cable modem causing havok

Postby pittsoccer33 on Fri Apr 11, 2014 12:10 pm

Thank you for that info. I will try flying without the router.

When I got the modem I finally reset my router and ditched WEP encyption. Maybe the new router setup is causing other problems. If thats the case I'll nuke it and start over.
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Re: New cable modem causing havok

Postby ffemtreed on Fri Apr 11, 2014 12:29 pm

pittsoccer33 wrote:Thank you for that info. I will try flying without the router.

When I got the modem I finally reset my router and ditched WEP encyption. Maybe the new router setup is causing other problems. If thats the case I'll nuke it and start over.


I wouldn't go without the router. Without the router your not going to have any DHCP and the settings on the computer get a little murky when directly connected to the cable modem. Just make sure your settings on your client are setup to get their settings from DHCP.

Start with just the cable modem and router setup. Use WPA (or WPA2 if all your devices support it) for your wireless encryption. WEP / WPA or any other wireless setting isn't going to affect anything that is hard wired into the router.
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Re: New cable modem causing havok

Postby pittsoccer33 on Fri Apr 11, 2014 12:42 pm

my main pc is

computer--->router--->cable modem

The cable modem DOES have a DHCP server mode that I can't seem to toggle off on the settings page. But from what I read on the internet it only becomes active when the modem isn't actually connected to the cable system.
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Re: New cable modem causing havok

Postby ffemtreed on Fri Apr 11, 2014 12:50 pm

pittsoccer33 wrote:my main pc is

computer--->router--->cable modem

The cable modem DOES have a DHCP server mode that I can't seem to toggle off on the settings page. But from what I read on the internet it only becomes active when the modem isn't actually connected to the cable system.



What you are probably seeing is how your cable modem gets its network settings from the ISP. These settings you don't have to worry about.

The DHCP settings you need to worry about are the DHCP SERVER settings where you can fill out an IP range, gateway and DNS servers. For a home network the default IP range / Netmask / Gateway should all be good. you might want to change the DNS server to google or OpenDNS.

I doubt that your cable modem has DHCP server capabilies, usually they are only available on a router or cable modem/router combo unit.

You should most defiantly use your router to function as a DHCP server.
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Re: New cable modem causing havok

Postby ffemtreed on Fri Apr 11, 2014 12:57 pm

pittsoccer33 wrote:my main pc is

computer--->router--->cable modem

The cable modem DOES have a DHCP server mode that I can't seem to toggle off on the settings page. But from what I read on the internet it only becomes active when the modem isn't actually connected to the cable system.



Ok, I just looked at the user manual for that cable modem and it seems it will function as a quasi type router since it will allow 32 devices onto the internet. Without a router your ISP would have to assign you a different IP address for every device on the network. 99.99999% of the time your ISP only assigns you 1 IP address. The manual isn't clear if it allows these 32 devices only if you have different IP's or if the cable modem does in fact do some type of routing (NAT or PAT)

you might need to see if there is a way to put that cable modem into bridge only mode somehow.

If the cable modem and your router are both doing DHCP you might have duplicate IP's on the network which would cause some of the intermittent problems you are having.
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