No answer if arp request from outside the private net

[wdsbln]

I need help to install a virtual box which provides some service via the internet.

I have a Linux host (archlinux) with an ubuntu guest. The network is bridged and in promiscuous mode.

The LAN is connected to the internet via a dlink router. The router is the DHCP server for the LAN.
So both the host and guest get their IP addresses from this router.

dlink: WLAN: 1.2.3.4 (for example), LAN: 192.168.6.1
host: 192.168.6.100
guest: 192.168.6.105

dlink port forwarding: 1.2.3.4:8888 -> 192.168.6.105:8888

VB 4.3.2 OSE

Everything works fine as long as only LAN devices are involved. The service at port 8888 can be seen
by any of these devices. But port 8888 at IP 1.2.3.4 is unavailable. The reason is, that
the arp request from dlink "who has 192.168.6.105? tell 1.2.3.4" will not be answered. Is this
a feature or a failure? Do I have a chance to solve this problem?

[Perryg]

This sounds like a question better asked at dlink.