1841 Router logs

[RickPine]

I have a home lab that I turn off when it is not in use. I spent a few hours trying to figure out why I couldn't reach my home ISP router after shutting down the Cisco 1841 that serves as the router to my home lab. After almost smashing the 1841 with a hammer, I decided to check if the ISP router had given away the IP address I statically configured as the entry point into the1841, and of course, it did. I now have added a static IP on my ISP router so it doesn't happen again. My question is, shouldn't the 1841 have complained about a duplicate address, Is this something a log server could have helped me resolve? I'm thinking about setting up a syslog server on a raspberry pi and I wonder if that would have been a good use, instead of doing all the checks I did. 

[David Ruess]

Hello,

Depending on how your ISP router is set up this will likely happen again as ISPs are always changing customer IPs to whatever they need it to be. When and if it changes will definitely vary. One solution is to configure your router interface as a DHCP client. So when the ISP device hands out a new IP then your router will accept it and should continue to work like normal.

You can use the ip address dhcp interface command and see if that can fix your issue. 

As far as being notified you might have seen some logs but that depends on how you access the device and the logs may not appear in the terminal window. 

Hope that helps

-David

[M02@rt37 · Accepted solution]

Hello @RickPine,

You're  right. In a situation where you configured a static IP address on your Cisco 1841 router and then the same IP address was assigned dynamically by your ISP router to another device, you would typically expect the Cisco 1841 router to log a "duplicate IP address" or "IP conflict" event.

Setting up a syslog server, like the one you mentioned on a Raspberry Pi, would indeed have been a good solution to help you identify and troubleshoot issues like this more easily. By configuring your network devices to send their logs to a central syslog server, you can have a consolidated view of all events and activities happening across your network.

@David Ruess is right, configuring your Cisco 1841 router's interface as a DHCP client is a viable solution to avoid IP address conflicts when your ISP changes your IP address. By doing so, your router will dynamically acquire its IP address from the ISP's DHCP server, eliminating the possibility of conflicts due to IP address changes made by the ISP.

The 'ip address dhcp' interface command would instruct your router's interface to use DHCP to obtain an IP address from the ISP's DHCP server. This can be a practical solution for a home lab setup, as it ensures that your router will always have a valid and non-conflicting IP address assigned by the ISP.

[RickPine]

Thank you for the insightful response.

I know I can find something by Googling, but could you recommend a free (as in free beer) Syslog software? I'm going to tackle this to continue learning. 

[M02@rt37]

You're welcome @RickPine.

Icinga is a free system monitoring package that also provides a collector for Syslog messages that can be filtered by severity level. Runs on Linux.