Problem on user's home network, Internet by XFINITY. Venting as much as anything.

I do in-house IT and just completed a frustrating call with one of our users. To put this in perspective, he lives 1.5 - 2 hours away (D.C. area). I don't make home calls, certainly not that far away, unless users agree to a) reimburse our mutual employer or b) I do the work on my time and they make it worth my while. I used to be more amenable, but found that is merely an invitation to being taken advantage of.

Anyway, so several weeks ago, this user started complaining that his laptop doesn't work wirelessly from his home. He insists the problem must be with the laptop, even though I pointed out several times that the laptop works fine on the office network, wired or wirelessly. Our systems get their network configuration through DHCP, which should "just work" on nearly any home network. His rebuttal is always that his iPhone, iPad and family PC work on his home network. And I always respond that doesn't mean the problem isn't with his network. He responds skeptically, and asks how that is possible. I've explained several times that the problem could be with the DHCP service(s) on his home network, at which point he gets a "deer in headlights" expression. I provided an Ethernet cable in case the problems were with his wireless network. He reported that this does seem to be more reliable, but still not consistent. He eventually admitted that sometimes the laptop does work on wireless (or Ethernet), but not always.

So he calls me from home today to report his laptop isn't connecting to the Internet. I had him:

• Open a command prompt and run ipconfig. His computer had a DHCP-assigned 10.0.0.20 address and default gateway 10.0.0.1 (same address as DHCP server). Turns out the gateway/DHCP server is a TC8305C gateway/router.
• Successfully pinged 10.0.0.1 and 8.8.8.8 (well-known Google-controlled public IP address).
• Run netsh int ipv4 sh dnsserver. This showed a DHCP-assigned DNS server address of 192.168.15.1. Odd, but could be a valid config if that address is for a reachable DNS server... Nope, no response to DNS query and not pingable.
• At this point, he asks if I can't just remote to his computer like I usually do.  I responded that I'm working towards that goal, so I can run some diagnostics on his network. Our users are members of the local Network Configuration Operators group on their computers; lots of globe trotters that connect to many different networks. But at the moment, I was fed up and wasn't about to walk him through statically configuring a DNS address.
• Let me remote to a family PC on the network that was connecting to the web. In the process, I find out this is a PC on loan from a family member and he doesn't have the admin password.
• ipconfig returns similar results to the laptop, except that the DHCP-supplied DNS addresses are 75.75.75.75 and 75.75.76.76, well-known Comcast DNS servers. WTH? At this point I'm thinking either the DHCP server has a reservation for the laptop and is handing out an invalid DNS server address, or (more likely, in my opinion) there is a rogue DHCP server on the network.
• Tried running DHCP Find (from Symantec). But this requires admin privileges to communicate on any networks, so attempt fails.
• Oh in the meantime, I explain why they're seeing bogus "YOUR COMPUTER IS INFECTED!!!!!" pop-ups in Chrome and remove the responsible "Coupons" extension.
• Unsuccessfully tried signing on the router at http://10.0.0.1. None of the suggested (Google search) usernames/passwords work.

So tomorrow, I think I will again try running DHCP Find and/or dhcploc. This time I'll walk him through statically assigning a DNS server address on the laptop and do my testing from the laptop.

If you have any suggestions on usernames/passwords for the TC8305C, I would appreciate it. Or at least let me know if Comcast Support will supply the information if he (the customer) asks.

Thank you for listening! 🙂