“Multiple PC's - Battery Backup - Fixing UPS IP Address”

By Ron Stultz

25 March 2007

In previous parts related to battery backup, I covered how I selected an uninterruptible power supply (UPS), how I connected it, etc. In this part, hopefully, I will cover the last aspect of using an APC Smart UPS with a local area network (LAN).

As reported in other parts on battery backup, the goal of acquiring an UPS was for the UPS to command all computers on my LAN to gracefully shutdown at a power event. APC’s Network shutdown software installed on all of my LAN-based PC’s was to communicate with the UPS and be told when to shutdown by the UPS. 

When I initially configured the UPS for an IP address on the LAN, I used HyperTerminal to set the Network Management Card in the UPS to IP address 192.168.1.100 and for a while, APC Network Shutdown Software did communicate with the network card in the UPS, but then I started getting “Can not communicate with network card” every time I checked the UPS status of any of the computers on my LAN. What? 

Another one of these, complexity breeds only more complexity sort of things.  

I use a Linksys WRT54G router, to which my 3 tower computers are connected via Ethernet cables and I use the 4^th Ethernet port on the router to go to the APC Smart UPS. 

Now in the past, the fact that the router controlled IP assignment had not bothered me in any way but now, I could not let the router assign a new IP to the APC UPS every time the router felt like it (power off and on sequence). 

So, for the first time, I had to go into the router and tell it to limit the number of IP address it assigns so that I could fix the UPS IP address and the router would not change this. 

How? In my Linksys router there is a place that lets me define the starting IP address to use on my network and also the number of IP addresses, the router can assign automatically. In my case, I changed the default 192.168.1.100 to 192.168.1.2 (one is reserved for special broadcast messages or something) and also told the router to only assign IP address between 2 and 9 or a total of 8 IP address.  

Now, using HyperTerminal and a serial cable, I told the UPS to used 192.168.1.100 as its IP address (again!). 

Now I went into my 3 tower computers and assigned each a static IP address.  

How? 

I went into network connections, the properties and finally TCP\IP and unchecked “get IP address automatically” and then proceeded to enter the IP address I wanted for each PC. In the case of my main computer, I made it 192.168.1.10 or just beyond the IP addresses assigned by the Linksys router. Also note that I made the default “Preferred DNS server), the base IP address of my router or 192.168.1.1. 

So, now I have stable, unchanging IP addresses for the PC’s on my LAN and they can communicate with the fixed or static IP address of my APC Smart 1500 UPS. 

I personally did not come across in my readings on the APC on a network, anything about adjusting the router but in retrospect, it makes every sense. Just took me a while to figure out the problem and then how to solve it. 

So, in summary, if you are installing an APC Smart UPS with a network management card (NMC), you must ensure that your router does not change the IP address or else all attached computers will loose communications with the UPS and never received the graceful power down command at a power event.