Tuesday, March 12, 2013

Can IP Addresses "Go Bad"?

This is going to be a very technical post. So, I apologize to all the non-geeks out there. Feel free not to read this.

I'm having this problem at home and at work and it's driving me crazy. I don't know exactly what forums to post to because it affects Windows and Mac machines so it's not anything specific to one platform.

I'm referring to IPs that simply decide that it will no longer work. Here is the scenario...

I have a computer, server, device, whatever. This machine as been running fine for weeks, months, years. Then one day NOTHING, no speako. What am I talking about? Ping is one. Let's say I have three computers:

What will happen is that one day will no longer "talk" to but it will "talk" to .20. 20 can see both 5 and 10. And 10 can talk to 20, but not 5.

It is that strange. I could have 100 computers on the same network, same subnet. And one day computer A will no longer talk to 30 of those computers, but the other 70 will talk just fine.

It's not a firewall issue. If I were to change the IP address of .5 to .6, it will suddenly talk on the network. if I get a fourth computer and change its IP to .5, it won't be able to talk to .10 just like the other computer. It's specifically that IP address, nothing else.

Over time the IP address remains "blacklisted" weeks or months later it still will be unavailable. Restarting networking equipment doesn't fix it. Restarting the computer doesn't fix it. Flushing ARP tables doesn't help.

This is the strangest problem I have encountered ever. I don't know what to do.


Peaceman17 said...

Did you ever figure this one out?

Unknown said...

No, never did. It hasn't happened to me for a number of years.

Peaceman17 said...

We just tried restarting a few of our switches, and ur kids like it's "fixing" the problem. No idea why still.