RDP over VPN to Server 2012-based hosts is sluggish with many disconnects, Server 2008-based hosts experience normal performance

consider following scenario:

we have multiple customers mixed environments of server 2008 r2 , server 2012 r2 vms.  access servers administrative purposes, vpn each customer's site sonicwall global vpn clients, rdp each machine. 

when rdp vms running server 2008/2008 r2, session performance normal, , disconnections/hangs rare.  when rdp 2012/2012r2 vms equivalent hardware resources, on same network, , on same hypervisor, rdp connection quality meter shows 1 or 2 "bars", sessions sluggish, , disconnections constant.  have reconnect same vm 6 or 7 times in ten minute period. 

here's gets interesting:  if you're on customer's network (say sitting @ 1 of pcs) , rdp 2012 vms having trouble, session performance normal.  in other words, it's when vpn access used, performance suffers.  suggests vpn or firewall traverses misconfigured, but if that's true, why rdp session performance 2008-based vms unaffected when vpn in same way?

as said, ruled out hardware resource limitations.  tried turning off client redirection features (printers, audio, etc.), and downgrading color , other 'visual experience' settings, no avail.  , performance problems occur when rdping on vpn multiple windows pcs, running 7 8.1, it's not machine that's having trouble establishing stable sessions.

any thoughts?

hi,

if click on connection info icon, show connection 2012 r2 using udp?  if yes, have tried disabling udp (via gp setting) on 1 server , testing again?

the thought vpn isn't handling udp reason.

-tp

Windows Server  >  Remote Desktop Services (Terminal Services)