1 PC + 3 MACs + Router + Cable Modem + SPI = ?
Posted on 2004-09-15
Here’s an interesting one for you guys. I *think* the problem is resolved, but I’m not 100% sure. I’d like to explain the situation, and then ask for an explanation or two from some of my techies fellows here. Here goes:
Yesterday, I got a call from a guy who has 1 PC, 2 Macintosh boxes, and 1 Apple Laptop. All are hooked up to a Netgear router, which is then plugged into a cable modem. I didn’t write down the model of the Netgear router, but it’s a non-wireless model and it has 4 ports in the back + the WAN port. No wireless in the equation at all. The problem is that the router kicks them all off the “net” at random times, all machines, at the same exact time. Sometimes after a minute, sometimes 15 minutes, sometimes after an hour or two. I told him I would come out in the morning and check it out.
Today, I went out on site to troubleshoot his network. Turns out, everything is set up pretty clean. Everything looks good. He could not tell me if getting kicked off “net” means kicked off the home network, or just kicked off the internet/web. While I was working on his Apple Laptop we got kicked off, and I noticed that the WAN settings for the router went completely blank. We only had the one computer powered up at the time, but I could still connect to the router, so I am going to assume that he was meaning they were all kicked off the internet.
Not wanting to waste the guy’s time and charge him a huge fee for drinking coffee at his computer desk while waiting for his router to hiccup again, I went through a few of the suggestions that I had read here… changing the MTU to 1492, looked at the possibility of spoofing the MAC address, etc.
Then I saw a little setting down by the MTU box, called SPI with a radio button for on and off. It was set to on. I decided that since the SPI setting was about the only thing that looked out of place to me, I decided to disable it and see if it made any difference. Well, afterwards, we browsed the internet for 45 minutes while discussing his plans for future network expansion (including wireless, security, differences between a switch and a router, differences between a wireless router and a wireless access point, etc, etc) and we were able to stay on the network the entire time!
Through looking around on the internet, I have found the SPI stands for “Stateful Packet Inspection”, and I have the garnered the idea that it has to do with security… but, I don’t understand how enabling this feature would cause network problems. Could someone PLEASE explain this? Get as technical as you’d like, as I dig details… but, please don’t BS me too much. I’m wearing my good shoes.