I appear to have stumbled across a fairly
substantial bug, although i'm not 100% sure on the steps to reproduce.
Symptom:* Local LAN Host fails to be able to ping or ARP router on wired or wireless connection, when that system's IP is set as one of the Internet DNS Servers in "Internet Settings". This also means no outgoing traffic from that host will work, BUT internal LAN traffic TO that host, will still function (SSH etc)
Steps to reproduce:* Reserve an IP for a system on your LAN (eg. 192.168.0.30 -- referred to as SYSTEM1 from here on out)
** NOTE: Definitely does NOT matter if the IP is inside or outside of the DHCP range.
* Renew IP on SYSTEM1 for changes to take effect where necessary.
* Ping router from SYSTEM1- all should be fine.
* Go to Setup> Internet> Manual Internet Connection Setup
* Set the "Primary DNS Server" field to the internal IP of SYSTEM1 (ie. 192.168.0.30)
* Save changes
* Ping router from SYSTEM1 - fail.
* on SYSTEM1 "arp 192.168.0.1" returns "-- no entry"
Points which may affect outcome and are untested:
* SPI enabled in my case, disabled with no effect
* Spoofing check enabled, disabled with no effect
* Arp command above was on a Linux host, but problem affects Windows and Unix alike.
* DNS relay is set to off in my example, but also doesn't work when set to on.
Theory:Routing is automatically setup by the internet connection settings page to route the DNS traffic via WAN regardless of IP range. Therefore, ARP requests reach the router (unproven... and unprovable) and replies are sent out of the WAN interface. Therefore, no ARP, no MAC reference, no ping-ability or another other connectivity outbound. Inbound traffic to that host still functions.
Technical backing:I'm a Linux Systems admin by day

I would greatly appreciate if anyone could give this an attempt, and report back with their findings?
I've raised a support reference with D-Link already, and will keep you posted with progress (Fault ref: 724915 in case anyone needs it!)
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See also:
http://forums.dlink.com/index.php?topic=46615.0