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grgarFlag for United States of America

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Comcast DHCP assigns single DNS same as Default Gateway

Had a problem today where 3 of 5 computers were not connecting to Internet through DHCP, although one of the two computers did have DHCP enabled and was connected. The other connected computer had a static IP address.

The odd thing was that the DNS server assigned both by DHCP and set statically was only a single Primary DNS. There wasn't an Alternate assigned - and the DNS was the same as the Default Gateway.

3 of the computers would not connect with DHCP even with a ipconfig /release, /renew done. But they did connect when I set static IP addresses. The site IP address is 23.x.x.x and the computer IP addresses (including the one assigned by DHCP) are 10.x.1.xx, while the Default Gateway and DNS are 10.x.1.1 (and the DHCP server, as stated in ipconfig results is 10.x.1.1).

Comcast did replace the modem router on Saturday. Does any of this make sense? Thanks
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David Johnson, CD
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You can always over-ride this in your router or your ethernet adapter settings, I uncheck assign dns automatically and use open-dns 208.67.222.222 and 208.67.220.220 myself
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I was aware of Google's public DNS, but I started to read something on "why not to use a public dns" and just left it go. Thanks for the info. I wasn't aware of those dns addresses, but my main question (which I hope to hear from Comcast today) is why those dhcp settings would be given out as such. And, secondly, why dhcp isn't working on at least 3 of the computers.
is this a comcast router that has multiple outputs?  (all in one box cablemodem/router)
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ASKER

Yes, it is. I believe it only has 4 ethernet and it is also a wireless router, too - as well as a modem.
Have you checked to ensure that the cable from the router to the computer is good? Try switching ports on the router and seeing if there is any difference? Was this working previously?
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ASKER

They had problems with Internet connectivity and sporadic website access last week. Comcast was out, and then out again on Saturday when they installed a new modem/router.
Could be bad hardware.
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Comcast said that they only reassigned a new static IP address on Saturday, which is the 23.x.x.x. I thought with Comcast, it was them that assigned the DHCP addresses and therefore the local static addresses - which are the 10.x.x.x. Where is the 10.x.x.x addresses originated from, wouldn't they be from Comcast?
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David Johnson, CD
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Sorry I never got back to this. Comcast replaced the modem/router. I set the DNS to static and reset DHCP for computers.