Saturday, January 15, 2011

Windows 7: IP Address Conflict: The Ol' Switcheroo

As described in a previous post, after approximately two centuries of trying to resolve an "IP address" conflict among the computers in my home network, traveling across thousands of miles of Internet highways in search of wisdom, I had happened to notice Event Viewer, and had started to use its error messages to figure out where the problem was.  Information from those messages led me to examine reports from my modem's internal webpage, among other things.  I had finally stumbled across what seemed like traces of a rational approach to troubleshooting network problems:  I would go into Control Panel > Administrative Tools > Event Viewer, would identify the error messages relevant to the network situation, and would try to figure out what they meant.  I was now engaged in that figuring-out process.

The concept seemed to be that my brand of DSL modem had just one DHCP address:  Just one computer would get it.  There was, in theory, a process where the computer coming to the party last would get its turn at the modem.  That was not what was happening on my system, though.  I was seeing that computer B was hogging access to the modem.

Unlike most home networks, I was not using a router.  The reason was that my router had stopped working during these ethernet wars.  I don't know if my network screwed it up, or if it was just taking a break, or what.  I had debricked it, as described in another previous post, and had otherwise played around with, and had given up on it until its replacement arrived in the mail, a week or so hence.

What I was using, instead, was a Netgear FS605 v3 switch.  This was not a wireless device, which was fine; my home network was entirely wired.  I was not clear on the differences between routers and switches, within this context, and that was part of what I wanted to understand now.  But mostly I wondered why the switch was not arbitrating successfully among computers.  I had used this switch for substantial chunks of time, over the last couple of years.  It had not previously had a problem in letting multiple computers share a single incoming ethernet line, such as the single line coming in from the DSL modem.  Was I remembering things wrong?  Or had it, too, somehow gotten fried by all the network action that had seemingly toasted my router?

To explore these mysteries, I ran a search.  This search led to a drawing of a system with a router and another drawing of a system with a switch.  Now I saw what I had been misunderstanding.  Basically, a router could serve as a gateway, while a switch could not.  From the perspective of a home user looking out upon the world, a switch had to be on this side of a gateway.  The gateway could be a computer or a router.  When I had previously used the switch to arbitrate among multiple computers, as I now recalled, I had done so in a university residence setting, where the university itself provided a gateway.  In other words, a switch could be within a network, but it could not mediate between, say, a home local-area network (LAN) and the Internet as a huge wide-area network (WAN).

But couldn't my combination modem/router provide that function?  I searched for insight.  One user reported connecting a cable modem (or combination modem/router) to a switch.  A webpage said, likewise, that a modem could be connected directly to a LAN switch.  Another search led to a discussion suggesting that the problem with a switch might be that the ISP (in my case, AT&T) would allow only one connection to the Internet at a time, whereas my switch was attempting two or more.  I wasn't sure I understood that.  But the matter seemed to be cleared up by a definitive statement:

Routers are also the only one of these three devices [i.e., routers, switches, hubs] that will allow you to share a single IP address among multiple network clients.
On this basis, it appeared that my network problems had been due to (a) a bad router and (b) my mistaken attempt to make a switch function as a router.  The question now was whether the router had been bad indeed.  My computers could still communicate with it, as discussed in previous posts, so the acid test would be to plug in the replacement and see what happened.

So I went out to Wal-Mart and got a Belkin Connect N150, model no. F7D5301 v. 1.  Their setup procedure didn't seem to work quite right, so I called their tech support at 877-736-5771.  Within ten minutes, I was up and running on both machines.  No connect issues.  Time to dump the old router.  I wasn't sure how to test the switch, to see if it was at all still good, so I just shelved it.



I did later get an "IP address conflict" using the new Belkin router. This happened after I briefly experimented with another Linksys router, a WRG54GS. The solution seemed to be to unplug the Belkin router's power, plug in all ethernet cables, let it sit for a minute or so, plug it back in, and type "ipconfig /renew" in a command window on each computer. I actually typed "ipconfig /release" first, in each of those command windows, but this gave me an error, so that didn't seem to be part of the solution.