Managemet network esxi nested randomly lose

HI guys!,,

i,ve 4 vApps with 7vms each ( 2 vcenter, 1Dc, 1 nexenta and 2 esxi 5.5)

my problem only only happens on esxi, these esxi lose the connectivity randomly.

I,ve configured all portgroups of vshield with promiscues mode and forged transmit and works all perfectly less esxi. These esxi lose the connectivirty randomly but i do ping to esxi  then esxi dont lose the connectivirty.

i Always need restart management network from dcui and i do ping

DO you know about IT?

thanks in advanced