Diagnosing DHCP Issue on New Modem/Router Setup - No Internet Access

[DHCPIssues]

I'm having trouble setting up a new internet connection, and I've done a lot of research and tried a lot of fixes, but nothing seems to work. So, basically at this point what I need help figuring out is whether this problem is caused by my ISP (which would be better for me) or my modem (in which case I'll have to RMA it, which I'm hoping against).

Anyway, I am trying to set up a Cox Preferred 100 cable internet connection (10 up / 100 down) with the following equipment that I purchased:

• 
  Modem: ARRIS SURFboard SB6183 - Refurbished, firmware version 9.2.0.0-GA-3.29-NOSH
  Router: ASUS AC1300 RT-ACRH13 - Brand new (not currently in use)
  PC: HP Pavillion Desktop (Windows 10)
  Ethernet Adapter: Realtek PCIe FE Family Controller

Right now, I just have the modem connected directly to the computer through ethernet:

[Coax wall outlet] -coax-> [Modem] -ethernet-> [Computer]

The issue is that while the modem appears to be connected to the network (the send/receive/online lights are all on, and the upstream and downstream signal levels are all at good values), the computer cannot connect to the internet. I called Cox Support and activated the modem over the phone and can see on my account that the modem's MAC address is correct. However, while on the network I can't even access the modem's configuration page at 192.168.100.1. I can access it while the modem is establishing connection, but as soon as all the lights turn solid, it shows up as unreachable (ERR_ADDRESS_UNREACHABLE in chrome). The only way to access it is by setting a static IP (I use 192.168.100.2, which is outside the modem's DHCP range), but even after setting a static IP I can't connect to the internet.

So, I think this is an issue with DHCP. If I run Windows diagnostics, I get the following:

and here is the output of /ipconfig all, with a 169.254.X.X IPv4 address:

Windows IP Configuration
   Host Name . . . . . . . . . . . . : User-HP
   Primary Dns Suffix  . . . . . . . :
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
Ethernet adapter Ethernet:
   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Realtek PCIe FE Family Controller
   Physical Address. . . . . . . . . : XX-XX-XX-XX-XX-XX
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   Link-local IPv6 Address . . . . . : fe80::e46a:XXXX:XXXX:XXXX%17(Preferred)
   Autoconfiguration IPv4 Address. . : 169.254.XXX.XXX(Preferred) 
   Subnet Mask . . . . . . . . . . . : 255.255.0.0
   Default Gateway . . . . . . . . . : fe80::242:XXXX:XXXX:XXXX%17
   DHCPv6 IAID . . . . . . . . . . . : 2991XXXXX
   DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-18-XX-XX-XX-XX-XX-XX-XX-XX-XX
   DNS Servers . . . . . . . . . . . : 2001:4860:4860::8888
                                       2001:4860:4860::8844
                                       8.8.8.8
                                       8.8.4.4
   NetBIOS over Tcpip. . . . . . . . : Enabled
Tunnel adapter isatap.{CB71E26B-D8E0-438C-8146-186D827249CD}:
   Media State . . . . . . . . . . . : Media disconnected
   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Microsoft ISATAP Adapter #2
   Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes

and ipconfig /renew fails with this message:

Windows IP Configuration

An error occurred while renewing interface Ethernet : unable to contact your DHCP server. Request has timed out.

The logs from the modem show a number of errors, but I don't know if any of them are significant or just normal.

Interestingly, I am able to login to cox.com and reset my modem remotely from the website, whatever that means. So far, I've tried rebooting the modem and my computer a number of times, using a different computer, using different ethernet/coax cables, resetting the LAN controller on my computer, reinstalling drivers for the LAN controller, running ipconfig /release, /flushdns, and /renew, factory resetting the modem, and more. I have also tried connecting my router to the modem, but the router indicates that my "ISP's DHCP is not functioning properly". At this point, I think all I really need to know is whether it is most likely a problem with the NIC or with Cox's network.

Thanks a bunch in advance.

 

[bill001g]

Cable modems only give you 1 ip address and it can be kinda picky which device it gives it to. The method that tends to work is to turn off both your PC and your modem. Let the modem fully boot. Turn on your PC and it should get a IP address. Problem is you can now not connect your router without going through the same process. You pretty much must power cycle the cable modem every time you plug something different into it.

 

[t53186]

You are correct about DHCP, you should get an IP address from DHCP. First thing to confirm is your ISP does in fact support using that modem.
Here is a link to the manual https://arris.my.salesforce.com/sfc/p/#30000000kUAL/a/a00000001dMM/6jnqOWm_Tq5Jc35YYQKIETvEfxvpUlntHS36B_FwFmU
Which you probably already have, but you need to connect to the modem and be able to look at the status screens and confirm you are online with your ISP, those logs don't look like you are online and connected.

 

[DHCPIssues]

You are correct about DHCP, you should get an IP address from DHCP. First thing to confirm is your ISP does in fact support using that modem.
Here is a link to the manual https://arris.my.salesforce.com/sfc/p/#30000000kUAL/a/a00000001dMM/6jnqOWm_Tq5Jc35YYQKIETvEfxvpUlntHS36B_FwFmU
Which you probably already have, but you need to connect to the modem and be able to look at the status screens and confirm you are online with your ISP, those logs don't look like you are online and connected.

Cox does support this modem, and I have looked at the manual. Here's the status screen when I connect to the modem:

To me it looks like it's connected (the values match what's in the manual, and the signals are within parameters).

 

[bill001g]

There is not much you can really configure a modem is really simplistic and most stuff is negotiated with the ISP equipment automatically.

There is not a lot too this. Your PC will send out messages asking for a IP. The ISP should detect this and send you one though the modem.

You could try wireshark and see if you find anything interesting but I suspect you will see your PC sending out DHCP requests and not getting a response. You never know. There is a tiny chance this is a firewall setting in your PC but most times nothing blocks dhcp.

You might try your router and see if it gets a IP on the wan port. Again you must power cycle the modem before you plug the router in.

If nothing works then you likely have to call your ISP they may not have fully activated your account.

 

[DHCPIssues]

Turns out it was something on Cox's end. I had already called twice with no results, but I decided to try the chat help, and whatever the guy did, it fixed it. Maybe it's because I said it was DHCP, but I don't know. Thanks everyone!