RT-AC5300 w/ Xfinity Gigabit - dhcp issues.

[unixwizzard]

I am running my 5300, with firmware 384.12 and is connected to a DOCSIS 3.1 Motorola MB8600 modem.

The problem I am having is when for whatever reason if I have to power down the 5300, when I power it on, the router no longer grabs the dhcp IP from Comcast. This is what I see:

Thinking it's just a slow handshake, I have already tried waiting it out, and gave up after about an hour. It will sit there like that until I do one thing: reboot the modem.

I believe this started with version 384.10, or maybe 384.10_2. I had been ill and did not get a chance to do any real troubleshooting until now.

Anyway, when I take both the modem and router offline (power off). When I started things back up, I followed the standard: Boot modem first, then when online, boot the router. This no longer works, as the router never gets the IP and I get the above error message on the router - again until I reboot the modem - a power off reboot, since now for some reason, even though the router is up, it cannot connect to the modem - that is also a new thing that never happened until recently.. Before this, as long as the router was up, I could get into the modem config and do a soft reboot if needed.

It only happens with cold boots of the router.. I could soft reboot the modem and router all day and when they come up, I get the IP address and connection immediately. The order in booting does not matter.

Now.. to throw a wrench in everything, I have a spare, a RT-AC3200, also running 384.12, and I hooked that one up and I got the exact same behavior - after a cold boot, the only way to get a dhcp IP from the ISP, is to reboot the modem.

Any ideas?

 

[ApexRon]

Now.. to throw a wrench in everything, I have a spare, a RT-AC3200, also running 384.12, and I hooked that one up and I got the exact same behavior

Here are my thoughts:

1. When you remove the Ethernet cable from the back of the router and plug it into a PC does DHCP work every time?
   1. If it does not work every time, then it could be the Ethernet cable or the modem
   2. If it does work every time, then since you have two routers that exhibit the same problem it could be firmware but I doubt it since most other people don't have that issue or it could be the modem. My modem is a Netgear CM600 with is DOCSIS 3.0

Beyond that the only thing I could suggest to "swap until you drop" (old work expression)

 

[Jumpstarter]

I am running my 5300, with firmware 384.12 and is connected to a DOCSIS 3.1 Motorola MB8600 modem.

The problem I am having is when for whatever reason if I have to power down the 5300, when I power it on, the router no longer grabs the dhcp IP from Comcast. This is what I see:

Thinking it's just a slow handshake, I have already tried waiting it out, and gave up after about an hour. It will sit there like that until I do one thing: reboot the modem.

I believe this started with version 384.10, or maybe 384.10_2. I had been ill and did not get a chance to do any real troubleshooting until now.

Anyway, when I take both the modem and router offline (power off). When I started things back up, I followed the standard: Boot modem first, then when online, boot the router. This no longer works, as the router never gets the IP and I get the above error message on the router - again until I reboot the modem - a power off reboot, since now for some reason, even though the router is up, it cannot connect to the modem - that is also a new thing that never happened until recently.. Before this, as long as the router was up, I could get into the modem config and do a soft reboot if needed.

It only happens with cold boots of the router.. I could soft reboot the modem and router all day and when they come up, I get the IP address and connection immediately. The order in booting does not matter.

Now.. to throw a wrench in everything, I have a spare, a RT-AC3200, also running 384.12, and I hooked that one up and I got the exact same behavior - after a cold boot, the only way to get a dhcp IP from the ISP, is to reboot the modem.

Any ideas?

make sure you are only using basic setup options for lan and wan at first.

 

[Jumpstarter]

If you are using IPV6 make sure these are set correctly as well

 

[Jumpstarter]

If these steps work. then you should be good to go, if they don't, then you need to unplug routers Ethernet cable from modem and select factory reset option with the clear NVRAM selected .

Then once the router is back up turn it off , refresh the modem by unplugging the modem from the wall plug and then plug it back in, Then finally once all the lights on the modem are back to looking normal, plug in your routers Ethernet cable back in. power back on your router, and reconfigure things manually making sure each of the settings are set like above to confirm everything is working.

 

[unixwizzard]

make sure you are only using basic setup options for lan and wan at first.
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seriously I need to have UPnP enabled?

 

[Jumpstarter]

You can test it without, those are just default options. If you do leave it on make sure you leave on secure option.

 

[unixwizzard]

make sure you are only using basic setup options for lan and wan at first.
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another thing.. what does the dhcp SERVER on the router have to do with the dhcp CLIENT.. that is the issue - obtaining IP from ISP.. not getting IP from the router.. more clarity.. all my clients get IPs from the router fine..

the router is not getting the IP from the ISP

 

[Jumpstarter]

It is just recommended as basic settings to eliminate out bad settings on users end.

 

[unixwizzard]

If these steps work. then you should be good to go, if they don't, then you need to unplug routers Ethernet cable from modem and select factory reset option with the clear NVRAM selected .
View attachment 18471
Then once the router is back up turn it off , refresh the modem by unplugging the modem from the wall plug and then plug it back in, Then finally once all the lights on the modem are back to looking normal, plug in your routers Ethernet cable back in. power back on your router, and reconfigure things manually making sure each of the settings are set like above to confirm everything is working.

really.. reset the damn thing.. again? I just finished setting the thing up from scratch..

christ maybe it's time to dump ASUS for something else

 

[Jumpstarter]

really.. reset the damn thing.. again? I just finished setting the thing up from scratch..

christ maybe it's time to dump ASUS for something else

Alot of times it is not always the router sometimes it is the isp and the modem,but you have to separately eliminate the router from all possibilities to know if it is the modem and isp.

 

[unixwizzard]

Here are my thoughts:

1. When you remove the Ethernet cable from the back of the router and plug it into a PC does DHCP work every time?
   1. If it does not work every time, then it could be the Ethernet cable or the modem
   2. If it does work every time, then since you have two routers that exhibit the same problem it could be firmware but I doubt it since most other people don't have that issue or it could be the modem. My modem is a Netgear CM600 with is DOCSIS 3.0

Beyond that the only thing I could suggest to "swap until you drop" (old work expression)

already thought of that, swapped ethernet cables already

it's option 2, happens every time, and only recently

anyone have a DOCSIS 3.1 modem they can loan me? ain't renting from ISP and going through all that hassle, especially switching everything back if the problem remains with the rental

 

[Jumpstarter]

already thought of that, swapped ethernet cables already

it's option 2, happens every time, and only recently

anyone have a DOCSIS 3.1 modem they can loan me? ain't renting from ISP and going through all that hassle, especially switching everything back if the problem remains with the rental

Good luck to you. I hate it when things don't work right either.

 

[RMerlin]

Try toggling the DHCP frequency on the WAN page between Aggressive and Normal - some ISPs don't like aggressive mode for instance, which can lead to your MAC being blacklisted for a certain period of time. Also double check what's in the MAC clone field, you generally want this field to be empty, unless your ISP has particular requirements.

Also, try turning off your modem for at least 10-20 minutes, to fully release any existing lease on their end (just rebooting the modem isn't enough, typical cable equipment will simply resume the previous connection unless the modem disappears for an extended period of time).

 

[b-rubble]

I also had this same issue with by 1GB comcast / CM1000 docsis3.1 / AC-5300 combo. Every single time I would restart the router I would get the ISP DCHP not functioning issue . Screwed around with the router config for several days until I discovered the problem was the modem. The solution was to always power down both - then on the restart, wait until the modem had established link to ISP before powering up router. Works every time now.

 

[unixwizzard]

I am running my 5300, with firmware 384.12 and is connected to a DOCSIS 3.1 Motorola MB8600 modem.

The problem I am having is when for whatever reason if I have to power down the 5300, when I power it on, the router no longer grabs the dhcp IP from Comcast. This is what I see:

Thinking it's just a slow handshake, I have already tried waiting it out, and gave up after about an hour. It will sit there like that until I do one thing: reboot the modem.

I believe this started with version 384.10, or maybe 384.10_2. I had been ill and did not get a chance to do any real troubleshooting until now.

Anyway, when I take both the modem and router offline (power off). When I started things back up, I followed the standard: Boot modem first, then when online, boot the router. This no longer works, as the router never gets the IP and I get the above error message on the router - again until I reboot the modem - a power off reboot, since now for some reason, even though the router is up, it cannot connect to the modem - that is also a new thing that never happened until recently.. Before this, as long as the router was up, I could get into the modem config and do a soft reboot if needed.

It only happens with cold boots of the router.. I could soft reboot the modem and router all day and when they come up, I get the IP address and connection immediately. The order in booting does not matter.

Now.. to throw a wrench in everything, I have a spare, a RT-AC3200, also running 384.12, and I hooked that one up and I got the exact same behavior - after a cold boot, the only way to get a dhcp IP from the ISP, is to reboot the modem.

Any ideas?

Follow-up.. I went and reset my RT-AC3200 and installed the stock ASUS firmware.. could not duplicate the error - with the stock firmware, factory reset and all default settings, I am able to pull an IP from the ISP immediately after a cold restart of modem and router.

Ditto on my backup TP-Link Archer C7 v4 - so that should rule out ethernet cable and modem.. right?

I will try then to do a reset on the 5300 keeping the Merlin firmware on it and see what happens.. being it's the 4th I may not get to it until Fri or Sat - depending on how drunk I get and stay I am not looking forward to rebuilding the manual local dhcp setup .

 

[unixwizzard]

I also had this same issue with by 1GB comcast / CM1000 docsis3.1 / AC-5300 combo. Every single time I would restart the router I would get the ISP DCHP not functioning issue . Screwed around with the router config for several days until I discovered the problem was the modem. The solution was to always power down both - then on the restart, wait until the modem had established link to ISP before powering up router. Works every time now.

see now my case is the opposite.. I have to bring up the modem, then the router, then cold-boot the modem to get the IP.. Just in case, I am also working with an Xfinity engineer to see if anything is funky with the new modem firmware.

 

[unixwizzard]

Try toggling the DHCP frequency on the WAN page between Aggressive and Normal - some ISPs don't like aggressive mode for instance, which can lead to your MAC being blacklisted for a certain period of time. Also double check what's in the MAC clone field, you generally want this field to be empty, unless your ISP has particular requirements.

Also, try turning off your modem for at least 10-20 minutes, to fully release any existing lease on their end (just rebooting the modem isn't enough, typical cable equipment will simply resume the previous connection unless the modem disappears for an extended period of time).

Will try aggressive vs normal (current setting).. unfortunately the second idea won't work - Xfinity caches the lease for far longer than that.. several days I was told.

 

[Jumpstarter]

Will try aggressive vs normal (current setting).. unfortunately the second idea won't work - Xfinity caches the lease for far longer than that.. several days I was told.

Yes that is correct i've seen comcast hold the same IP's for a while. The easiest way to force a change though, is to do what rmerlin said , but to also connect up a different router as well. Comcast seems to change it if it detects a different mac address.

 

[RMerlin]

Will try aggressive vs normal (current setting).. unfortunately the second idea won't work - Xfinity caches the lease for far longer than that.. several days I was told.

It's not just about the lease, but about the actual "session". For example, my ISP will only give you one lease at a time. If I switch my router with another, it will be unable to obtain a DHCP lease unless I turn the modem off for at least 5 minutes. But regardless of this, if I put back the original router after a few hours, that original router will still obtain the same IP it used to have before. My ISP caches the lease it allocated to its MAC, however it just needs that 5+ minutes downtime before it will accept to assign me a new lease.

So if you are switching back and forth between two routers, you might need to have a similar 5+ minutes downtime (the length probably varies between ISPs, I've seen users on American ISPs go with 20 minutes just to be safe).