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user_a61075
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Tuesday, May 31st, 2022 6:31 PM

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MG8702 DNS

Just upgraded to a Motorola 8702 modem/ router combo, purchased 3rd party.

Local clients receive 192.168.0.1 for DNS and don't have internet access unless I manually change it in each device to 8.8.8.8 (Google dns). How do I change this within the router so my devices will receive 8.8.8.8 via the router?

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2 years ago

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EG

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108.6K Messages

3 years ago

That device acts as a DNS forwarder / DNS relay which is why it gives the LAN / network clients an IP address that is the same as the gateway address. It's supposed to be that way. You just set the DNS server addresses to whatever you want them to be in each of the device's network settings and they will be forwarded / assigned to the individual network clients.

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user_a61075

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@EG​ Unfortunately, that will make it a bit cumbersome when other devices (Kid's friends, etc.) come over and I'm not available to manual help them edit their device's dns. There has to be a simpler solution.

3 years ago

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EG

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108.6K Messages

3 years ago

I haven't been able to find it in any of the manuals that I've researched so far. Maybe you or someone else can.

Others should not have a problem if they have their devices set to obtain the DNS servers automatically.

Good luck with it !

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Jim721

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3 years ago

1. In order to setup a static DNS in the MG7550 (different from the one assigned by the cable provider), you must first disconnect the coaxial cable connection. 
   *Your computer must be connected to the modem via
ethernet cable

2. Once the coaxial cable is disconnected, bring up a web browser (i.e. Internet Explorer, Chrome, FireFox, Safari etc.)

3. In the Address Bar (URL) type 192.168.0.1 and hit the Enter key

4. At the login page:
    Username:  admin 
    Password:   motorola  (all lower-case)

5. At top right corner Click Advanced

6. Click Status

7. Click Connection

8. Scroll down to section titled "IPv4 DNS Servers"

9. Select "Disabled" for "Obtain Automatically from MSO"

10. Type in the desired settings for Primary DNS and Secondary DNS

11. Click Save

12. Reconnect coaxial cable to the modem, then wait for modem to sync back up

This is for a different gateway but it is likely very similar. 

(edited)

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EG

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@Jim721​ 

I saw that too. But it was for a different model so I didn't post it. Hope that works for them ! Thanks for finding that Jim !

I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.

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3 years ago

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user_a61075

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Result after updating: The dns info shows up in the router "connection" page as I prefer them, but it still does not push them out to a device. I will probably try resetting the router completely this weekend and start fresh.

(edited)

3 years ago

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CCStephanieT

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Hello @user_a61075  Thank you for reaching out to us on our community forums. Have you tried reaching out to the manufacturer of the modem/router combo? 

I no longer work for Comcast. 

3 years ago

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user_a61075

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3 years ago

Update: A full reset seemed to work until the next day, then devices had no service. Had to manually add dns into each device. 

No, I haven’t reached out to the manufacturer yet. 

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user_a17d3f

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@user_a61075​

The same thing happened to me with a MG8702 Motorola cable modem purchased through Amazon. I had been using it with no issues since April 2021. Suddenly around middle of May 2022, all my DHCP client devices stopped being able to access the internet. I tracked it down to the fact that the MG8702 had stopped relaying DNS requests. It was still routing packets OK. Pinging IP addresses worked fine, just names did not resolve.

To be clear, the MG8702 is acting as a DHCP server. It was set to get the DNS servers from the WAN (Obtain from MSO) and it got 75.75.75.75 and 75.75.76.76, which are the xfinity DNS servers. I verified with nslookup that those DNS servers do respond correctly. However, the MG8702 does not pass those DNS server IP addresses to its DHCP client. Instead, is specifies its own address 192.168.0.1 as the clients' DNS server. Even if I change the DNS servers under Status/Connection/IPv4 DNS Servers to the google ones 8.8.8.8 and 8.8.4.4, it does not pass those to the DHCP clients, just its own 192.168.0.1. That would be fine if it relayed the queries, but it doesn't. It just times out.


c:\>nslookup
> google.com
Server:  [192.168.0.1]
Address:  192.168.0.1

DNS request timed out.
    timeout was 2 seconds.
DNS request timed out.
    timeout was 2 seconds.
DNS request timed out.
    timeout was 2 seconds.
DNS request timed out.
    timeout was 2 seconds.
*** Request to [192.168.0.1] timed-out


This started happening on May 20th, 2022. I rebooted the modem many times and finally I factory reset it and reconfigured it.
I think that fixed it and it started relaying DNS again.
Then I went on vacation and came back today 6/23 to find that this is again happening. The modem is not relaying DNS again.

There doesn't seem to be any firmware update for it. The current software on it is Software Version 8702-19.3.18.
I am thinking of buying a different cable modem but I hate to have to make that expenditure when everything else is working OK.

Another option would be to disable DHCP and run a little linux DHCP server somewhere on the network with the right DNS servers being advertised. But that introduces another point of failure. I would prefer to have everything on the same device.

3 years ago

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zip21222

Contributor

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160 Messages

3 years ago

An Amazon review for the MG8702:

Static DNS not fully supported
By [redacted] on August 5, 2021

You can set static DNS to your choice
But if it loses connection, it will reset back to the default even though the admin console show that it is still set to yours.
You have to change it, click save, then change it back, then click save again in order for it to get updated and use your setting once more.
Really stupid... am returning it.

argh.....

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