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I have a Linksys WRT54GS router flashed with DD-WRT that I'm trying to get a connection on behind a Cisco DPC3010 cable modem. I can get a connection just fine when I plug my computer in directly into the modem, but when I plug the router into the modem, it refuses to deal the router an IP. My ISP is Cox, if that matters.

Here's the basic setup for my router right now:

WAN Connection Type

  • Automatic Configuration - DHCP
  • STP - Disable

Optional Settings [all default]

  • Host and Domain name blank, and MTU on Auto

Network Setup [all default]

  • Local IP - 192.168.1.1
  • Subnet Mask - 255.255.255.0
  • Gateway - 0.0.0.0
  • Local DNS - 0.0.0.0
  • DHCP Type: DHCP Server
  • DHCP: enabled
  • Static DNS 1: 192.168.1.1
  • Static Dns 2: 8.8.8.8
  • Static Dns 2: 68.105.28.12

Things I've Tried:

  • MAC address cloning to have my router's MAC match my computer's MAC (My computer is capable of connecting to the cable modem just fine)

  • Using all kinds of different DNS servers. I doubt this would solve this kind of issue, though

  • Powering down both the router and modem, fully powering up the modem, and then powering up the router

  • The Cisco modem isn't a router and doesn't have any configuration utilities of any sort; just a page that displays basic information about the modem (MAC address, serial, etc)

  • Changing the WAN connection from DHCP to manually match the info that the modem deals to my computer. Here's the ipconfig for my computer connected to the modem:

    Screenshot

I'm really not sure where to go from here. Any advice?

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3 Answers 3

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Most cable internet providers requires you to use the same MAC address used before.

Here are few steps that you can try:

  • Check if your WAN interface can negotiate DHCP configuration;
  • Try to use your computer's network configuration on WAN interface (IP address, subnet mask, default gateway and DNS);
  • Try to ping to internet IP address (e.g. default internet gateway and 8.8.8.8);
  • Check if DNS is resolving with: nslookup google.com

If not, try all steps cloning your computer ethernet MAC address to router's WAN interface.

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  • The only options under WAN configuration are either automatic configuration with dhcp, or use of a static IP. Neither worked. I have already tried using my computer's configuration, and I stated that in my original question. There's 100% packet loss when I ping an internet IP. No connection is established. DNS isn't resolving. I have had my computer's ethernet MAC cloned throughout this ENTIRE process. Also, I'd like to note that I know for a fact that the router works, hardware-wise, since I was using it in a previous setup. And as I said, my cable modem works with my computer. Jul 24, 2014 at 4:36
  • Try to disable WAN connection, enable Assign WAN Port to Switch option and try to connect to internet using your router as a simple bridge. It should work, if not, you may have a problem with your WAN port.
    – denisvm
    Jul 24, 2014 at 4:46
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I literally had the same problem and took the same steps as you with no luck. However I came across this same issue in another forum and their solution worked for me.

http://www.dslreports.com/forum/r27092115-NE-DPC3010-issues

In short, it seems the modem configures (only once) to the first device it's connected to when powered on. So, the modem does not reconfigure if you swap between devices (PC to router1 to router2 to..) if the modem power is kept on.

Suggested solution:

  • Power off both modem and router
  • With your modem plugged into your router, power on your modem only and let it boot up fully
  • Power on your router
  • Then it should work at this point

I was able to switch between different routers and PC following this method.

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This happened to me too, with an Actiontec MI424WR rev D router with DD-WRT. (Recently updated via its web-interface to "actiontec-mi424wr-firmware.bin", r42872 (20200410), which is the newest one that doesn't fail to update (files 7564MiB or larger don't "take"; this is a separate problem).)

I inserted the MI424WR between my PC and my existing (other-brand, stock firmware) router, and tested it heavily (a few days and many megabytes via wired and wireless). Then I went to install it elsewhere, to replace someone's very old router. Not once did it get an IP address from the modem via DHCP. I cloned the MAC address of their old router; no DHCP. I tried giving it, as a static IP address, the same address (and netmask and DNS servers) that the old router received via DHCP; no Internet access. I replaced their 11-year old ISP-provided Arris modem with a new ISP-provided Arris modem. Still nothing. Back home, it is almost the same. I installed the MI424WR between my PC and my 2-year-old ISP-provided Arris modem, and it seemed to get an IP address from the modem just once, and lost it. But when I connected my old router back to the modem, and inserted the MI424WR between my PC and the existing router (again, like I tested it), it took a few more restarts than I expected, but it works fine (again). (I am connected that way right now.)

I don't know what I am missing. Maybe I didn't leave the modem OFF long enough. Maybe I didn't wait long enough after powering up the modem before powering up the MI424WR.

Maybe the modem tracks more than just MAC; maybe I have actually to call the ISP to flip the "secret bit". But my ISP is very permissive about MAC addresses. Just now I changed two bytes of the MAC address of my existing router's WAN port. The router took a while, but I did not restart the modem. The router got DHCP of a new outside IP address that differed in 3 bytes. I changed the MAC address back, and I got back my previous IP address. (I have known this for a while. My ISP's DHCP gives each MAC address a 24-hour lease. Changing the MAC gets back the same IP address, unless the lease ran out. Recommendation: Clone your old MAC whenever you change routers, if only to stay at the same IP address. Possible hack: If one or many users change their connected router's MAC every few seconds, eventually the ISP's DNS server will run out of IP addresses. If that happens, it will be "stuck" until the oldest unrenewed leases expire. It could re-issue old IP addresses that have been inactive the longest, but at risk of address collision. Maybe cable-modem DHCP tables include modem addresses, which would let it block collisions caused by forced re-use (and block spoofed traffic too). Maybe cable-modem DHCP limits the number of IP addresses assigned to each modem, voiding the least-recently used one (if needed) when assigning a new one.)

I will update here if an answer arrives.

Meanwhile, a weak "answer" is to insert a non-DD-WRT router, wired-only (or disable the wireless port) between the modem and your DD-WRT router. The non-DD-WRT router will get an IP address from the modem, and the DD-WRT router will get an IP address from the non-DD-WRT router, and all will have Internet access. Two routers, two bottlenecks. And if you need port-forwarding, you have do it twice (once in each router). (By the way, port forwarding or port-range forwarding (I forgot which) severely slowed down one of my routers.) One possible minor benefit is that computers connected to the DD-WRT router can "see" (address) computers connected to the non-DD-WRT router, but computers connected to the non-DD-WRT router cannot "see" computers connected to the DD-WRT router.

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