port forwarding not working on virtual interface

[therobust]

Hello guys,

i have installed a zentyal server and configured it for port forwarding.
i have assigned the public IPs to WAN interface and created a virtual interface as i have multiple Public IPs.

WAN: 115.xx.xx.18
WAN:virt : 115.xx.xx.19
LAN: 192.168.10.1

Server1: 192.168.10.2
Server2:192.168.10.3

the port-forwarding rules work for WAN interface and i can access .18 from internet however the port-forwarding doesn't work for WAN:virt interface

here are the port-forwarding rules for virtual interface:
interface: WAN:virt
original destination: 115.xx.xx.19 (tried 'zentyal' option also)
original destination port: 80
protocol: All
source: Any
destination IP: 192.1688.10.3 (local IP of the webserver)
port: same


Kindly suggest any changes if i need to...

regards