Cable modem OK. Router OK. But they can't communicate...
Posted on 2006-04-10
A customer's XP desktop PC connects to the internet fine when connected directly to their Comcast "RCA DCM315" cable modem. But when I tried to add either of two routers (EITHER my linksys wrk54g router, or their Dell TrueMobile 2300 wireless router) -- we can't ping the internet -- wired OR wirelessly.
I tried using the RESET Button on all three devices, and also power cycling. I also dropped the PC firewall. I checked the network device TCP/IP settings and found nothing. (everything I saw was set to AUTO -- DHCP, DNS, etc)
Both the wireless adapter and wired adapters of the test PC connect to BOTH routers. I can ping the gateway (router OR modem, separately - never both at same time.) And I kept re-cabling back and forth, to ensure the direct "PC to modem" setup still worked, and it always did -- although often it required power-cycling the modem.
The dell router's "internet explorer" based config util has a diagram that shows the wireless and the LAN (wired) connections working fine, but has a red X over the "internet" connection (to the modem.)
I didn't think to use the "router status" menus (internet explorer), until I had left.
I confirmed that my travelling test router (the wrkg4g) DOES till work at MY home with MY home comcast router. (as opposed to the customer modem, described above)
When connected directly to the cable modem, ipconfig says the gateway is
when connected to the Linksys router, it's the default
for the Dell router, it's
The weirdest thing is -- I got the dell router working fine, a few weeks ago. The customer says they kept losing wireless and had to keep connecting directly (wired), and then that stopped working -- but I can't be sure of her observations.
So now I don't know if the change is in the PC, the router(s), or the modem.
REVIEW / BOTTOM LINE:
(1) the cable modem seems to be working fine, when connected to PC directly.. BUT
(2) neither router -- not even my trusty, dependable, test router (a linksys wrk54g) -- communicates with the modem.
(3) all 3 devices were re-set to factory settings. no help.
(4) I got the modem and dell router to work together fine a few weeks ago
Any guesses as to what's causing the problem?