Odd behavior from my home network...

pamccabe

Ok, this just happened to my home network and I am at a complete loss as to what to think. I am watching TV and my daughter comes up to me to tell me that the wireless internet is down. Cute girl I say and tell her to hand me her iPod. I look it over and she is connected and getting an IP from my server. Everything looks good but nothing loads, meaning websites. I get up, go to my network/computer. All the lights are on my Netgear router. I sit down at my computer and am able to ping my switch, my server, and my router. However, I can't get online. I restarted my computer, my server, and the Netgear router. All came back online, however this time the WAN port on my router was flashing orange, not good. I grabbed a spare router I had laying around and plugged that in, still can not connect. The really odd thing, is that the new router grabbed a IP from a dhcp server that is not on my network. 192.168.100.101. I made sure the DHCP server feature was turned off on the spare router. However, it was still pulling an IP of 192.168.100.101. To start over, I setup my network like it was originally, to have the same result. Fine, at least I am back to square one. I then unplug the Ethernet cable from my original router's WAN interface and plug it directly into my computer. I do an ipconfig /release and /renew to see it has grabbed a 192.168.100.101 IP... the lights on my cable modem were blinking periodically, not normal behavior. It seems like my cable modem, which was plugged directly into my computer, was handing me an IP address. The modem is behind my desk for safety reasons (kids) so I reset the modem. Boom, back online immediately. It just seems like my cable modem was acting like a DHCP server. As I understand it, these modems act like a dsu/csu, converting an analog signal into a digital signal and acting like a DHCP client for my ISP to assign whatever IP range it has for me. Does anyone know anything about this behavior with the Samsung Motorola modems? Can they be set to hand out IPs like what I experienced? The IP scheme I have setup in my home is not in the range that I was being assigned. About to do some searches but thought I would ask around.

CodeBlox

It probably wouldn't be the modem handing out the address, more likely the service provider. Maybe they are using carrier grade NAT? Carrier-grade NAT - Wikipedia, the free encyclopedia

deth1k

Your cable modems internal IP is actually 192.168.100.1, depending on the model you will be able to get to WEB GUI of your CM to get some diagnostics info, such as SNR (signal to noise ratio) and you Download/Upload rates. If for whatever reason modem loses it's signal to ISP's CMTS network it will start dishing out IP addresses acting as DHCP server.

pamccabe

Great information, thank you guys!

wes allen

You might also look into putting your modem into bridge mode, if it isn't already. Otherwise you might be double NATing which can cause some delay, and you can't access your firewall remotely for VPN/port forwarding, if that is something you wish to do. That might also mean moving your PPoE info to your firewall as well.