Why does my new router hate my PC?
May 7, 2014 1:24 PM   Subscribe

We recently brought in a new broadband provider to the house. Everything is working swell, except the desktop PC refuses to establish a steady connection to the new router. What am I missing?

The desktop has always been connected via ethernet cable to the router which has been in the same room. Now, with the new router downstairs, I'd like to connect it to the ethernet port in the wall that runs down to the office where all the cables are aggregated.

Problem is, the PC refuses to retain a solid connection. It will connect, and I can surf fine for a few seconds, but then the interface reports 'cable disconnected' and the connection drops. The lights on the router end and the port on the PC both go completely dark, indicating a complete lack of connectivity (right?). A few seconds later it connects again. Rinse and repeat.

The PC connects just fine to the old router. My laptop connects just fine to the new router using the same wired wall jacks; I've tried multiple jacks around the house and they're all the same - the laptop connects rock solid, but the PC continues to flake out. I've got our DVR and DVD player connected via the wall jacks and they're also both fine. I've tried different cables, made sure I'm not using a crossover cable, etc. I've verified the adapter settings are identical between laptop and PC. Gone through every setting I can find on the admin interface of the new router. That specific PC just refuses to get cozy with that specific router.

Original router, which the PC works just fine with, is a netgear WGR614. New router is a Cisco DPC3828D.
PC ethernet card is 'Realtek PCIe GBE Family Controller' integrated on the motherboard. It's a couple years old. Laptop interfaces is also Realtek, 'PCIe FE family', on an HP laptop, also a couple years old.

Key differences are:
PC is plugged into a wall jack now, with a cable run of less than 50 feet to the new router. Previous config was a cable directly to the old router. But multiple other devices work fine so I don't see it as a cable problem.
Cisco functions both as a cable modem and router. Old router is just a plain router, with an uplink cable from the DSL modem.
New router is DOCSIS 3.0; old router isn't. But isn't this just a protocol between my ISP and the router? Has nothing to do with my home network, right?

Old internet is still functional, and I can switch the cable from the wall jack to the old router and the PC will happily connect solidly.

I turn to you, experts of the internet. What else should I be looking at? Next step would be to go grab a separate network card and pop it in to see if there's something strange with the onboard interface, but since it works fine with the old router I'm not convinced it's broken.

Thanks in advance!
posted by SquidLips to Technology (6 answers total)
Response by poster: Before anyone asks, the behavior doesn't change whether I have DHCP enabled or configure a static IP. When the connection flakes out, I can't access the router admin console so it's definitely a connectivity issue.
posted by SquidLips at 4:05 PM on May 7, 2014

See if there's a firmware update for the router. Make sure you've tried every iteration of connection, to try to localize the issue. Also, remember that you don't HAVE to use the combination modem/router as a router. You can still use the dedicated router attached to the modem. Yes, DOCSIS 3.0 is just between the cable modem and the ISP. Also, in my experience, combination modem/routers suck horribly.
posted by destructive cactus at 4:30 PM on May 7, 2014

Start constant pings (ping -t ip.add.re.ss from command line) from the PC to the each router (so, 2 cmd windows), and ditto from the laptop. That will tell you whether the failure is happening in the first leg/router (both pings fail) or the second (only the ping from desktop to new router fails). Try tracert to an internet site and see how far it gets both when things are working and when they aren't. cmd: tracert for one of Google's public DNS servers.

Check nitty-gritty NIC settings, or uninstall and re-install the NIC. Pro-tip: download new NIC drivers before uninstalling NIC drivers. Boy I felt stupid!

Borrow a new-to-you NIC. Any IT guy probably has a hoard of them somewhere.
posted by Sunburnt at 4:49 PM on May 7, 2014

You can buy a cheap switch (not router) for like $30 and use that to connect your pc to. You can possibly also use your old router as a switch, too -- connect it to the new router using one of the computer ports (not the uplink port) and turn off dhcp-- that SHOULD work.
posted by empath at 7:46 PM on May 7, 2014

Best answer: It might be like a weird auto configuration issue with the port duplex/speed. Try setting your computer's ethernet settings to 100 Full and see if that makes a difference.
posted by empath at 7:48 PM on May 7, 2014

Response by poster: And we have a winner!

Old router only supported 10/100, new router supports 10/100/1000. Desktop NIC is Gigabit. House wiring is 11-year-old cat5e, probably not the highest quality since I was a cheapass at the time, so I'm thinking when the NIC saw that it could talk to the router at GB speed, it would try, and the cabling couldn't handle it, too much interference, etc. Laptop NIC is only 10/100 which is why it always worked.

Went into NIC settings. Forced speed to 100Mbps Full Duplex, but it was still flaky. After some additional research, I also turned on auto-disable gigabit, and disabled the "Energy Efficient Ethernet" setting, and it worked like a charm, been rock solid for an hour. The whole 100M vs 1Gb thing never occurred to me. Thanks for pointing me in the right direction!
posted by SquidLips at 10:44 PM on May 7, 2014

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