Help. This thing flaps on every export

Admin,

I really need some help on this. During all my testing the whole process worked well. Now that I'm ready to put my shiny new dhcp servers into production it doesn't work well. Yes the redundancy is working but it happens after every scheduled task where it does the export from the primary to the secondary. Export begins, failover occurs, a minute later it comes back to the primary. Every time this happens, my group gets an email that failover occured. I can't have this thing flap after every export! I run them fairly frequently but I still can't have this condiiton in our enterprise. What gives? Is it because I'm running this thing on some very fast servers and when you made this thing you tested on slower servers? How can I control this behavior? Can you add a check box to the dhcp redundancy configuration that allows me to set the number of failures that are allowed to occur before failover should take place? This seems like an easy thing to implement. How soon can I have it? I need this fixed or I'm sunk.

Thanks,

Theo22

In the file dhcp-backup.bat on your main DHCP server, check that the UNCpath is the same on all three lines, eg:

echo "exporting configuration" > "\\server1\c$\program files\dhcp-redundancy\Exporting.txt"
netsh dhcp server export "\\server1\c$\program files\dhcp-redundancy\DHCP-Backup.txt" all
del "\\server1\c$\program files\dhcp-redundancy\Exporting.txt"

Hi Admin,

Yes. All my UNC paths match. I added a line before the 3 lines in your example to rename the DHCP-Backup.txt so we can keep a history of our backups for about a month. Could this one liner to rename the backup file be what is borking this process? Shoud I just copy the the latest backup after the export runs instead of renaming the backup prior to the export? I don't understand how this could be causing the failover to occur everytime my batch file runs. What is the current timing mechanism of the dhcp-redundancy service? What is my window for doing an export before failover occurs? Our dhcp database is quite large. What if it takes 30 seconds to export it? Is that too long?

As I understand it, I thought the DHCP-redundancy process checks to see if the service is available on the primary server. What exactly is happening during the export and how does the DHCP-redundancy process know that it is just an export and not too failover? I understand that DHCP is unavailable during the export process but how does the DHCP-redundancy process differentiate this vs. a real outage?

Well, I've removed my one liner in my batch file to rename the backup file prior to the export and the failover still occured. Bummer.


By the way, I'm running this on Server 2008 R2 x64.
2.40GHz Quad-Core AMD Opteron.
4GB Ram.
Local data store.

Quick Question:

When you open the DHCP Redundancy Config GUI, at the very bottom there is "Directory of DHCP -Redundancy Files" and a text box to enter a path. Where should this path be pointing to? Should it be pointing to the same folder where my exported dhcp file goes to? The same directory as in my batch file? The same directory where "Exporting.txt" gets created and deleted? Or should this point to the folder where I unzipped/installed all the dhcp-redundancy files like the DHCP Redundancy Confige.exe, and the installation instructions and all the all other files?

Is the trigger that the DHCP-redundancy process uses to failover something like this?
The logic: If main dhcp server is unavailable (due to export) and there is no "Exporting.txt" file in the "Directory of DHCP -Redundancy Files" location, then failover. Does this sound correct?

So I think I answered my own question. All my subsequent tests have proven successful and failover is not occuring when my export runs anymore.

When I was finallizing my configs to put this into production, I changed the backup location in the bacth file. I did not match this new folder location in the DHCP-redundancy Config GUI in the "Directory of DHCP -Redundancy Files" location. So apparently this location must match the location where the Exporting.txt file is located. This must be some sort of lock file so the DHCP-Redundancy process knows not to failover during the dhcp export.

Phewwww. I feel so much better. This thing was working like a champ up until I started to change some of my configs. DOH!

Yes, that is correct. DHCP-Backup.bat creates the file Exporting.txt while the main DHCP service does the export, and the DHCP-Redundancy service looks if this file exists. While the file exists the DHCP-redundancy service ignores the status of the main DHCP service.