Help me understand my network | Howard Dierking


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(preface: I love my wife who, upon reading what I had originally written, suggested that I calm down and edit out some of the intro to this post)

I’m in the midst of a home networking _situation_ right now, and I’m hoping that one of you who undertands networking better than I do can help me understand what may be going on…

When we switched to cable-based Internet service a while back, I decided to go with an all-in-one router/gateway/DHCP server/cable modem – all in this tight little package. About that same time, I cancelled our phone service and switched to OOMA – nothing like having a single point of failure. However, I had never had a service failure – until yesterday.

Yesterday at around noon, our Internet service went down. I waited for a while because this was pretty common when we had DSL and it used to always come back up after a while. But the service didn’t come back up – so this morning I called Wave Broadband and they sent out a service tech. When the tech checked the ISP endpoint and my cable modem connection, everything checked out fine – but no service connection. We then reset the cable modem and noticed something interesting. I now had an Internet connection for one computer that had a wired connection to the router, but no others, and the wireless network was still completely down. The service tech said it must be a problem with my router and left.

So I did a little more digging. on running ‘ifconfig’ at the terminal, I noticed the following entry for interface ‘en0′ (which is my ethernet adapter):

inet netmask 0xffffff00 broadcast

Uhh, that’s not an allowable IP address from _my_ DHCP server (I keep things nice and local with – so where is it coming from?

Looking deeper with ‘netstat -nr’, I noticed the following

Destination Gateway     Flags Refs Use Netif Expire
default UGSc  60   0   en0

Ok, well that’s definitely not my gateway – so who’s is it – running ‘whois “n″‘ confirmed what I suspected all along – that my computer had its network configuration set through DHCP not through my DHCP server but directly by my ISP.

So the question is – why??

I called Motorola to see whether there were some firmware updates available. They told me that even if there were (there are), Motorola is not allowed to make them available as a download link because of some FCC rules stating that the ISPs must be the ones to distribute firmware updates – presumably to ensure compatibility with their networks. That said, the Motorola support folks were super-helpful – and led me to one other discovery: when I unplug the coax from the all-in-one, everything on my LAN works – my computer’s IP assigned from my DHCP server, and all my wireless devices can once again connect. However, the second I plug the coax in and the all-in-one downloads information from Wave Broadband, everything goes back to its screwed up state.

The Wave tech support people first told me that I didn’t really understand how DHCP worked and that everything was fine – and then later, after I pushed them on it, told me that there was a real problem, but that everything looked fine on the cable modem side of things and that because my device was not theirs, they refused to help me further troubleshoot the issue.

So what are some possible reasons for my network being so screwed up?? At the moment, only one computer (e.g. the one I’m writing this on) is capable of connecting to the Internet and my wireless network is down – presumably because it can’t assign IP addresses to the devices that are trying to connect to it. I’m not sure what’s going on or how to test to confirm, but I think that the configuration that my all-in-one pulled down from Wave is somehow disabling my DHCP server (and it looks like my router as well).

I don’t really have a ton of time to experiment, as I need to be able to get VOIP working again as well as ensure that my wife will have Internet access when I take my computer with me to work in the morning. However, I’m thinking that the best solution at this point is to separate my router/gateway/wireless unit from my cable modem. That’s historically been my philosophy and for whatever reason, I took a risk this time. Bleh. I’ve been looking at this unit for the router and will probably go with whatever cable modem is supported by Wave to ensure that they can’t as easily dismiss me in the future.

So, any of you with a deeper understanding of networking 1) have an idea of what could be going wrong here, and 2) how I could test for it?

Also, any general recommendations on my upcoming network setup redo?

Or, any similar horror stories you want to share to make me feel better? :)