I was finally able to run a live test. I thought I would share my findings here.
Just for clarification, the controller that would be Local1 in the diagram previously posted was still serving production while I ran these tests, so it will not appear in any of the testing descriptions.
Using only LMS and Backup-LMS (no VRRP defined)
* Two 3400 controllers running 6.1.3.4 (one as Master, the other as Local)
* Two AP-105 APs connected to a different VLAN than the controllers
* APs are assigned to a test group with LMS=Local2 IP address, Backup-LMS=Master IP address, LMS preemption enabled
* The AP VLAN has DHCP option 43 set to the Master IP address
> Controllers online and configured
> Plugged in APs: wireless network came online with APs tunneled to Local2
> Unplugged Local2 ethernet: APs switched to Master after about 10 seconds
> Plugged in Local2 ethernet: APs did not switch back to Local2 after 5 minutes (they remained tunneled into Master)
> Unplugged Master ethernet: APs went into endless boot cycle (wireless network down)
> Plugged in Master ethernet: Aps booted and tunneled through Local2
Conclusions from LMS / Backup-LMS test:
* I do not know why the APs did not revert back to the LMS when LMS Preemption was checked (enabled) unless I didn't give them enough time (5 minutes) to see that Local2 was available again. Even then, I think they still should have reverted to Local2 when Master went offline instead of rebooting.
* The APs obviously did not retain their LMS / Backup-LMS settings when rebooted (ie. they behaved as olino stated).
* In a power-outage scenario, if the master controller failed during the outage or the the APs restarted after the master failed , the wireless network would not come back online without intervention.
Using VRRP for Local and Master controllers (no Backup-LMS)
* Same two 3400 controllers running 6.1.3.4 (one as Master, the other as Local)
* Two AP-105 APs connected to a different VLAN than the controllers
* VRRP_M: primary=Master, secondary=Local2
* VRRP_L2: primary=Local2, secondary=Master
* The AP VLAN has DHCP Option 43 set to VRRP_M IP address
* APs are assigned to a test group with LMS=VRRP_L2 IP address
> Controllers online and configured
> Plugged in APs: wireless network came online with APs tunneled to Local2
> Unplugged Local2 ethernet: Aps switched to Master with only 2 lost pings
> Plugged in Local2 ethernet: APs switched back to Local2 with only 1 lost ping
> Unplugged Master ethernet: APs continued to operate
> Unplugged APs: wireless network went down (of course)
> Plugged in APs (Master still down): APs boot up and tunnel through Local2
> Plugged in Master ethernet: APs continued to operate
Conclusions from the VRRP test:
* APs have no problem with DHCP Option 43 being set to a VRRP address that is being controlled by a local controller.
* VRRP allows the APs to switch between controllers much quicker than using LMS/Backup-LMS.
* Any one controller can fail and the wireless network will continue to operate even if the APs are rebooted.
One last comment:
* I thought I saw something somewhere that made it sound like DHCP Option 43 could be used to specify more than one IP address for multiple master controllers, but there were no instructions or examples that showed how those addresses should be coded (separated with comma, space, or some other method). If so, the LMS/Backup-LMS scenario might not have behaved so poorly. However, since VRRP made the transition so much more quickly, I have no desire to pursue using the Backup-LMS setting.