Unexpected consequences – part 2.
An interesting story, but a good bit geeky. Two or three of you may appreciate it.October 14 the PCCC had a meeting where we showed everyone how to configure their router. Not knowing if anyone would actually bring their router to demonstrate, I took my secondary router out of my home network to demonstrate. My network runs
from the cable modem
to my VoIP router
to my wireless router
to my computers. Because it’s running all over my office and home, I have several downstream switches to redistribute the network to my workbench, etc.
When I left I connected the home network directly to the VoIP router and verified that my wife could get on the internet. The next morning, after I’d gone to a client’s, she called and said she couldn’t get online; despite having been connected a half-hour earlier.
Here’s where your eyes may glaze over if you don’t have your propeller beanie on …
I got home and sure enough, none of the computers could get online. I checked the settings and nothing seemed out of the ordinary. After about the third time I looked at the settings, I realized all the computers had IP addresses in the 192.168.
0.xx range. This is common – and what they had been last week – so it didn’t strike a bell to me. Then I remembered the VoIP router is at 192.168.
15.1. Since the settings require that the first three components of the IP quad be the same, there was no way the computers could get to the router and out onto the internet.
I discovered the last item I connected, after testing that the computers could get online, was actually not a dumb switch, but a router. This rogue router was giving out addresses in the 192.168.
0.xx range; in competition with the gateway at 192.168.
15.1. That router giving out addresses had not been in conflict when the VoIP and wireless routers were in series on the way to the internet. My wireless router was on the 192.168.
0.xx range as well so it didn’t matter where the computers got their address from.
To help you visualize my situation, there are some diagrams of my network here. (
http://bloghd.zaitech.com/images/UnexpectedConsequences.jpg)
End of super-geeking. Here are some details on how you get an IP address.Every computer on your network has an IP address. The “old-style” IPv4 is a series of 4 binary bytes represented in the decimal form
000.000.000.000. On a small home network, the first 3 bytes must be the same and the last byte identifies each device. On this small network, devices can only communicate with others that have the same first 3 bytes unless they go through a router.
Typically, when a computer comes on the network, it sends out a broadcast asking for someone to give it an address. If there’s a router or server on the network, it will assign the computer an address that no one else is (to its knowledge) using. The router actually associates this address with the unique ID of the network adapter. Thus, a computer with both a wired network jack, and wireless capability will have two different IPs.
When the router gives a computer an IP, it gives it a “lease” on that address for a period of time typically running from an hour to a week; depending on the settings. That means this address will not be given to another device until the lease is up. When the lease is up for renewal or if the computer leaves and returns to the network; the router will give it back the same address unless it’s been assigned to someone else in the interim.
My computers were able to get online after I connected the rogue router because they still had a 192.168.
15.xx address. The next day, when they went to renew their lease, the rogue router – which was not connected to the internet – answered first and gave them a192.168.
0.xx address. This kept them from communicating with the router that would connect them to the internet.
The moral of this story is, if you grabbed a router to extend your network where you should be using a dumb switch; be sure all your routers are set for the same address range. And be sure your rogue router is pointing back to the other as its default gateway.
