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borg389IT
Posts: 6
Registered: ‎07-07-2010

router as switch keeps flipping back to 192.168.1.1

I've got 2 linksys routers.  I used my older wired one as a switch. I am not plugging anything into the #1 connector.

 

I had set the IP address of the router to 192.168.1.2 because my primary router is 192.168.1.1.  For some reason, every few months, it resets to the default 1.1, causing my primary router to freak out regularly.

 

Is there a way I can make the 192.168.1.2 permament?

 

What sucks is that when it happens, I can't access that router from my main box.   When it resets back to the default, it obviously can't be accessed from the main network since something already has the 1.1 IP address.  Unfortunately, I don't have a box with a web interface on that sub network and can't add one at this time.


The only way I can fix it is to swap my main router with that one, and connnect via my main box to reset it back to 1.2.  As this interrupts other people in the house, and it's kind of a **bleep**, I'd rather avoid having to do this.

 

Any ideas?

Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: router as switch keeps flipping back to 192.168.1.1

Your old router seems to have a bad NVRAM which causes the loss of configuration after a couple of months. The router then resets back to factory defaults. This will also enable the DHCP server on the old router which means that some computers will get incorrect default gateway information. There is nothing really you can do about this except replacing the old router with a standard ethernet switch.

You could change the IP address of your main router, e.g. to 192.168.1.254 or 192.168.2.1. But it won't solve the problem that a reset will reenable the DHCP server on the old router...
borg389IT
Posts: 6
Registered: ‎07-07-2010

Re: router as switch keeps flipping back to 192.168.1.1

Oh well.


Thanks for the info.

 

At some point I will be upgrading my main router, and I'll put that in place of the other one.  For now, I just need to find a way to update the configuration through telnet.

 

I can telnet into the computer I have on that router.  I just don't know if I can telnet from there to the bad router and update the config that way.

Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: router as switch keeps flipping back to 192.168.1.1

Linksys routers don't have a telnet interface. You can only configure them through the web interface.

And again: telnet, web interface or anything else. When you have two devices using the same IP address in your network you won't be able to access them reliably. You should change the IP of the main router to avoid this situation.
borg389IT
Posts: 6
Registered: ‎07-07-2010

Re: router as switch keeps flipping back to 192.168.1.1

 


gv wrote:
Linksys routers don't have a telnet interface. You can only configure them through the web interface.

And again: telnet, web interface or anything else. When you have two devices using the same IP address in your network you won't be able to access them reliably. You should change the IP of the main router to avoid this situation.

 

You're half right.  If machine A is connected to router B, which is connected to router C, which is connected to machine D, and both routers have the same IP address, you can't connect directly from machine A to router C.


But I can connect from machine A to machine D still (I do it daily so if you are gonna tell me I can't, you're wrong), and I can have machine D connect to router C.  So I can telnet to machine D and have machine D run something that could fix it.

 

Obviously the solution is to set the IP of the main router to something different, but that would mess up other machines in the house on router A.   I will probably do it, but I really hate that I have to.

Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: router as switch keeps flipping back to 192.168.1.1

I'm fully right. If you have two devices using the same IP address in your network you can't reliably access them.

1. What you describe is something completely different. Of course you can connect from A to D. A and D don't have the same IP address. They could not access each other or anything else if they had the same IP address.

2. You did not connect routers. Your second router is set up as switch. Technically you have connected an ethernet switch to your main router. That's all. Technically this additional ethernet switch has internally a router attached which uses a static IP address. If you would connect both routers really as router (i.e. running through the WAN port of the second router) you could not even configure the second router the way you have it now because the router cannot have a IP 192.168.1.* on the WAN and LAN interface at the same time.

3. As it's a switched extension of your network of course some devices at may be able to access one of the conflict IP devices. But as I have wrote before: it's an unstable setup. You can be sure that you will be able to access the same device again after an hour of inactivity. The computers learn the MAC addresses and IP addresses of the computers in your LAN. If they don't know the MAC address they use ARP to find it.

It's undetermined what should happen if an ARP request delivers two different MAC addresses or if two different MAC addresses have been learned for the same IP address. The computer can either pick one and maybe it will stick to that one and ignore the other one (assuming someone using a fake IP address) or the computer will pick a random one and after ARP cache expiration will do the same again. Or the computer will refuse to use the IP address at all because of the conflict.

Thus if D can connect to C it may be luck or coincidence. But definitively not a reliable way of access. It may look completely different if router B chose to send out some broadcast traffic at some point of time which causes computer D to learn the MAC address of B for the conflicting IP address...

4. The best way to extend an ethernet LAN network is to get a switch. Then you don't have these kinds of problems. You could even get a gigabit ethernet switch and upgrade to gigabit if you don't have it yet...