Solaris IPFilter and IPMP
I just ran into the case where I had configured the Solaris 10 IPFilter subsystem on a machine that was using IPMP and was having some sporadic difficulties. It turns out that the stateful inspection feature (typically the “keep state” stanza) isn’t supported on machines where the inbound and outbound packets might be going through different interfaces. I believe this is only a major problem on active/active configurations, but it will also get you in the active/passive scenario when an address fails over to an alternate link. This is another reason to consider using dladm based link aggregations if your network topology supports it.