DNS at random stops functioning on Zyxel C1100Z Modem

[SidCharming]

Problem started yesterday and now I have to reboot the modem in order to get any name resolutions to function. I have a router connected to the Modem which is running DHCP. I have been running the configuration for over a year with no issues. From all network devices I get a response of can not PING www.google.com. I get the response "unknown host www.google.com" I went to my router and performed a ping from the command prompt to ping www.google.com... response was "no response". I unplugged the Modem, waited 30-40 seconds, plugged it in and waited. I performed 2 pings one to the IP address for the Modem and another to www.google.com. Once Modem is fully up, both are responding correctly. So that situation has now happened 3 times at random. I am wondering 2 things, does hardware kinda stop working? Should I consider a firmware upgrade (if it exists) I am a CenturyLink subscriber and this is a personally purchased modem, so I don't believe I will get much help from them. Thoughts?

 

[bill001g]

It could be the ISP DNS server. Try to put 8.8.8.8 in for the dns the router uses. If it still does it you can always hard code the dns in the pc to 8.8.8.8

 

[SidCharming]

It could be the ISP DNS server. Try to put 8.8.8.8 in for the dns the router uses. If it still does it you can always hard code the dns in the pc to 8.8.8.8

Oh, I failed to mention I have hard coded DNS in my DHCP to use OPENdns servers and not the ISPs... I could manually program each network device (PCs, TV box, Ipads, Ipods, phones, etc) but it seems like a pain for each new person to my WiFi network at the same time =\

 

[Solandri]

Are you sure it's a DNS problem? What happens when you try to ping a numerical IP address (e.g. ping 8.8.8.8) when you're suffering these DNS problems? If ping to the numerical IP address is also flaky, then you have a connection problem, not a DNS problem.

With DSL (both ADSL and VDSL), the most common connection problems I've encountered are:

• 
  ■Make sure you have DSL filters on all your phone lines (except the one the DSL modem is connected to). DSL uses the frequencies above the ~8 kHz used for voice. Without the filters, high frequency noise from other devices can get onto the line and degrade the DSL signal.
  ■If you have phone service on the line, do you sometimes hear static? That's a sign that the line is bad. Either there's a loose connection somewhere, or the plastic sheathing on the line has cracked and allowed water into the line. This will also degrade the DSL signal causing intermittent connection. Who has to fix it depends on whether this problem is in your home's phone wiring, or in the phone company's wiring to your house. The phone company will resist testing to see if the problem is with their line, and will always try to blame your equipment or home wiring even if there's no evidence of this. You will have to really push them to get them to test their line.
  ■Modem is overheating. Feel it with your hand. If it feels uncomfortably hot, it may be overheating. Sit it properly on its feet or in its base, raise it above the ground (don't put it on carpet), put it in a location with some air circulation (or even point a fan at it - lots of USB-powered fans you can use), don't place it on top of or right next to other hot equipment.

VDSL (and ADSL) will automatically ratchet down your speed in response to line quality issues. In my experience, it can take the modem a few seconds to "sync" again after a speed change. And if the line quality is so bad that it can't sync at the slowest speed, sometimes it'll just give up for a few minutes.

 

[SidCharming]

Are you sure it's a DNS problem? What happens when you try to ping a numerical IP address (e.g. ping 8.8.8.8) when you're suffering these DNS problems? If ping to the numerical IP address is also flaky, then you have a connection problem, not a DNS problem.

With DSL (both ADSL and VDSL), the most common connection problems I've encountered are:

• 
  ■Make sure you have DSL filters on all your phone lines (except the one the DSL modem is connected to). DSL uses the frequencies above the ~8 kHz used for voice. Without the filters, high frequency noise from other devices can get onto the line and degrade the DSL signal.
  ■If you have phone service on the line, do you sometimes hear static? That's a sign that the line is bad. Either there's a loose connection somewhere, or the plastic sheathing on the line has cracked and allowed water into the line. This will also degrade the DSL signal causing intermittent connection. Who has to fix it depends on whether this problem is in your home's phone wiring, or in the phone company's wiring to your house. The phone company will resist testing to see if the problem is with their line, and will always try to blame your equipment or home wiring even if there's no evidence of this. You will have to really push them to get them to test their line.
  ■Modem is overheating. Feel it with your hand. If it feels uncomfortably hot, it may be overheating. Sit it properly on its feet or in its base, raise it above the ground (don't put it on carpet), put it in a location with some air circulation (or even point a fan at it - lots of USB-powered fans you can use), don't place it on top of or right next to other hot equipment.

VDSL (and ADSL) will automatically ratchet down your speed in response to line quality issues. In my experience, it can take the modem a few seconds to "sync" again after a speed change. And if the line quality is so bad that it can't sync at the slowest speed, sometimes it'll just give up for a few minutes.

Solandri, These are great points... However I did and can ping a server directly by using their IP addresses. And for the record I did ping 8.8.8.8 specifically. My modem is located in my kitchen on the top cupboard in the open air. Nothing around it causing air restrictions. Location is not near a heat source or even sun light. I don't have a land line, so I have only one device plugged into the network.

Thanks, these are great suggestions and I will look closer to the box temperature at time of issues... I have a thermal thermometer gun to test it.

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