Router will not obtain IP address from ISP

[scovilletech]

Got a strange issue here. My setup is this: motorola cable modem connected into a tplink router. Last night I installed a new docsis 3 cable modem and then the tplink router would not get an ip address. It says in the log that no dhcp offer was received. I can hook a pc directly to the modem and get an ip and get on the internet just fine, but hooking up the router, no go. Have rebooted several times with no luck. I tried the unicast dhcp setting to no avail.

I swapped out the tplink router to an older slower linksys router and boom, gets an ip and connects fine. Just want the tplink to work since it is a gigabit router.

I thought about maybe something to do with gigabit vs 100 mb on the wan interface, but the modem shows gig connection and I have no way that I know of to change this setting.

Any ideas? I am stumped on this one.

 

[katz]

Maybe the obvious? A dead router?

I dealt with this very issue this past Saturday. Router appeared good, all lights blinking. Rebooted everything a couple of times...eventually came to the conclusion that it was dead straight out of the box.

Can you test the router on another network to confirm?

 

[scovilletech]

I might think that had the router not been working before the modem swapout. The router is not new and was working fine on the old modem.

 

[rsarceno]

You might have to call the ISP and register the router.

 

[compnet]

You might have to call the ISP and register the router.

Yup, or I think some motorolas have to be put in bridge mode to pass through to the router.

 

[katz]

I might think that had the router not been working before the modem swapout. The router is not new and was working fine on the old modem.

My error - I thought the router was the new component...

 

[YeOldeStonecat]

Assuming that the "modem" was provisioned when you put that new one in place, try pulling the power from the modem for 5 minutes. If it's a model that has a battery underneath...pull that too (most voice ones have that).

 

[katz]

Aside from pulling the power, would it not be better to press/hold the reset button until the lights go out to clear all settings? That how I usually bring our Comcast modems back to life after quirky stuff like this.

 

[YeOldeStonecat]

Can try it.....I don't think I've ever resorted to the reset button, we do a lot of Comcast setups.
OP, specifically which model modem?

 

[katz]

Can try it.....I don't think I've ever resorted to the reset button, we do a lot of Comcast setups.

Yeah, I think that is worth a try anyway. The job I had on Saturday where the router was dead...After replacing the router, I had to press/hold the reset button until the lights went off/on.

I tried the power cycling first, but that didn't do it in my case.

But yeah, most times a power cycle seems to do the job. I'm anxious to see what trick finally solves this one!

 

[YeOldeStonecat]

What model Comcast modems you talking about BTW?

 

[katz]

What model Comcast modems you talking about BTW?

I forget, lol - I've been so busy, I plain forgot. But I'm going back to that client one day next week & I'll check on it.

It's an older modem & might be a Motorola. It is a big, bulky cigar box shaped thing, heavy, has a battery in it & also telephone jacks.

 

[YeOldeStonecat]

I

It's an older modem & might be a Motorola. It is a big, bulky cigar box shaped thing, heavy, has a battery in it & also telephone jacks.

Ahh...on those (they're called MTA's when doing voice)...you have to yank the little battery underneath when you pull the power cord to "power cycle" them. Else if you don't yank the battery, it doesn't shut off, thus the whole point of clearing the memory of the existing MAC table doesn't happen. So when pulling the power cord to get it to "forget" the prior MAC address it was associated with, you also need to pull the battery.

//inserts caution about not needing to call 911 during this time..cuz the phone lines will be dead for a minute or three when you pull the battery.

 

[katz]

Thanks for that info. I've only ever seen a couple of them onsite. Are they "older" units? Are they rechargeable batteries? I didn't really take a close look at the battery.

At any rate, to clear out "everything", I usually go for the reset buttons on all devices.

 

[YeOldeStonecat]

At any rate, to clear out "everything", I usually go for the reset buttons on all devices.

On the managed static "gateways"....if I did that I think I'd have to call Comcast to have them reprovision it (upload that config file) again. The biz static modems take a bit of prep when initially setup, don't want to lose that.

 

[scovilletech]

Can try it.....I don't think I've ever resorted to the reset button, we do a lot of Comcast setups.
OP, specifically which model modem?

SB6121 Docsis 3 by Motorola