IPMP on the cheap with Solaris 10
By Dave Miner-Oracle on Sep 07, 2005
"The use of a dedicated test address for IP multipathing groups is no longer required as of Solaris 10. When test addresses are not configured on the interfaces assigned to a group, IP multipathing will detect interface failures solely by monitoring the IFF_RUNNING flag for each network interface. This requires that the network interface driver support link status notification, which is true of most recent network drivers in Solaris. For further information, see in.mpathd(1M) and the System Administration Guide: IP Services."
The end result is that IPMP can be done "on the cheap" if you only care to passively monitor the link status from the driver; if you want to do active monitoring using ICMP probes, it'll still cost you a test address dedicated to each network interface. Note, though, that in.mpathd can use IPv6 link-local addresses for this purpose, one small reason to think about getting to know IPv6.
My buddy meem the code minimalist was the implementor of this feature. Perhaps he'll see fit to talk about the details at some point.