Barracuda Load balancer LB VLAN documentation missing some really important points , specially about how you are going to manage the device while you connected to a Trunk port . 

Theoritically if you are connecting any device to a trunk port all the traffic destined to that trunk port must have a VLAN tag . Like subinterfaces we are creating on cisco device . 

In Barracuda LB , we have a subinterface like scenario and can tag the traffic . ( Advanced IP config page - create vlan - map any service to  appropriate VLAN ) , 

But if any traffic without a VLAN tag will be rejected from Switch port , unless there is a "NATIVE VLAN" for that interface . This is precisely happen when you try to manage LB through a trunk port . There is no option inside Barracuda to say management IP is on particular VLAN so the traffic will not be tagged . 

So you have to make "NATIVE VLAN" on switch if you want to manage LB though a trunk port . 

For example if you want to manage barracuda from DMZ vlan ( assume DMZ on vlan-10 ) enter follwoing command on Cisco switch trunk port . 

interface FastEthernet0/13
   switchport trunk encapsulation dot1q
   switchport trunk native vlan 10
   switchport mode trunk
end

Then you can manage LB from anywhere in VLAN-10 .

On a HP switch interface connecting to LB must be untagged for VLAN-10 and all other VLAN as tagged . 

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We faced tremendous difficulty with a Qatar client to find this out because Barracuda document not at all mentioned this . Hope they may include it in future editions .