Visitor
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2 Messages
ISP's DHCP not functioning - Fix for ASUS Router owners (probably others)
I'm posting this to assist others with the same issue. I recently upgraded my Xfinity Internet to a higher speed and purchased a new modem to support 1000Mbps. I prefer to manage my own hardware so I purchased a Motorola MB7621 modem and after working with Comcast, I got the MAC address updated and confirmed I was online with internet exiting the new modem. Then the trouble started. My ASUS RT-AC1900P router that had been working swimmingly with Comcast as of 1 hour ago would not connect citing DHCP errors from my ISP. Neither the posts on this site, nor anything from ASUS had clear guidance on this issue. The only thing that eventually worked for me was:
1. Be connected to your wifi network even though it's not getting Internet, you need to access the router only at this point.
2. Access your router admin (192.168.1.1) and find out your firmware number and place to update it MANUALLY.
3. Disconnect from your wifi network and get online somehow. I used my ethernet cable because I had internet to my modem, you could use a hotspot or whatever, just get online.
4. You'll then want to visit ASUS website, go to support, find your device, and DOWNLOAD the latest firmware. Then unzip it and remember that file name and location. https://www.asus.com/us/support/
5. Rejoin your wifi network, yes, the one that doesn't have Internet.
6. Go back into the admin portal (192.168.1.1) and upgrade your firmware using the file you downloaded and unzipped.
7. Do a HARD reset of the router using the button in the back. For some reason, the reset offered through the admin portal didn't seem to work.
8. Let the router restart and join the network called ASUS (this is what you did when you bought it)
9. Once you join it will ask you to set up a new network. Follow the steps that you did back when you bought it (Automatic IP, not Static).
10. Reconfigure your network SSIDs because the reset wipes everything out.
When your router tries to detect the network it will ask you to reboot your modem. This is the MAIN EVENT.
11. Unplug/shutdown the modem and restart.
12. ASUS will detect the Comast signal, do the configs and get you online, nothing else for you to do.
At this point, the modem correctly found the Comcast DHCP and other config information and connected. Note: I was 30 minutes from picking up new equipment at the cost of $200 so this like hitting the lottery.
As with most of the other posts, Comcast said they can only give advice on their own equipment which, I guess I understand and I'm sure it motivates a lot of people purchase their rental plans, but it's really not the customer service I needed and it's not like Comcast is Netflix at $20/month or whatever. If this is a common issue with anyone who upgrades modems, it's something that could be posted or at least available to customer service. Send me to a website, I'll do the work from there. Hope this info helps, I found a lot of solutions with a lot of random advice about changing DHCP frequencies ... that information is a distraction. This process worked for me but it took some time and frustrations.
RB_MD
Contributor
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19 Messages
3 years ago
Thanks so much for this!!
I had tried THREE different routers (all of them Asus) and was on the verge of calling FIOS for a switchover.
I followed your instructions and the router pulled an IP on the very first try.
Of course I had to restore all my router settings, but that only took minutes compared to the hours I'd wasted trying different routers...
Thanks again!!!
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RB_MD
Contributor
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19 Messages
3 years ago
Hmmm, just found something very interesting that I think is worth mentioning here.
A number of other posts here that discuss router DHCP problems suggest that you try plugging a single computer directly into the modem and see if that computer gets an IP. If that works, they suggest cloning the MAC from the computer to the router. I followed that advice, and like others here my router still couldn't get an IP, even using the cloned MAC.
I eventually found this thread and got things working (thanks again Daniji!) but just noticed that my router is still using a manually assigned MAC address, despite step 7 above doing a full hard reset on the router, which should have returned the router to using it's hardware MAC.
Even more surprising is that it's not the MAC I cloned to it in my earlier troubleshooting, but rather something completely different. Wondering exactly where this MAC could have come from, I did a wireshark lookup on it, and lo and behold this is what I got (actual MAC redacted):
xx:xx:xx Comcast Cable Corporation
How in the world did that happen? Does the handshake that occurs in step 9 above actually include Comcast assigning a new MAC address to the router? I suspect that clearing that manually assigned MAC would put me right back where I was earlier, unable to get an IP no matter how many times I reset the modem.
The geek in me really wants to do some experimenting with this, but I just can't afford any more downtime right now, so maybe in a few weeks, when I can afford some downtime, I'll do some testing and update this post.
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RB_MD
Contributor
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19 Messages
3 years ago
So I kept wondering where that Comcast-owned MAC could have come from, and it occurred to me to look in my router's DHCP logs. Sure enough, that is the MAC of my Flex box.
I am 99.9% certain that I did not clone that MAC to my router, so I'm still wondering how in the world it got there.
Just to satisfy my curiosity, I followed Daniji's steps again, but this time I removed the cloned MAC from my router config and skipped the hard reset in step 7. To my surprise, everything worked as before, my router got an IP address just fine, and the router is definitely using it's hardware MAC now.
Wish I could figure out what was goin on there, but hey, it's working, and I try to never look a gift horse in the mouth, so take all this for what it's worth and best of luck getting your setup working.
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Dryst
Visitor
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1 Message
3 years ago
I just faced this issue today after upgrading from an Arris SB6141 to a Motorola MB8611. I own an older Asus RT-N66U wireless router. I have never seen this issue until Comcast updated my Internet speed and told me I needed a new modem. The Arris never showed this issue when connected to my wireless router. With the newer MB8611, I immediately faced this issue with the Asus wireless router, and I could not get an Internet connection at all.
I followed these steps and had success on the first attempt. This looks like an Asus bug that needs a fix in all of their routers.
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user_e19d5e
Visitor
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6 Messages
3 years ago
Sounds like just a factory reset of the router was needed here. [Edited: "Language"] but it is what it is
(edited)
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loopytrixie
Visitor
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2 Messages
3 years ago
Same exact problem and this is the only thing that worked. THANK YOU.
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