Hi,
we use in our network a DGS-1510 D-Link
we have on network 2 Subnetworks with 2 Gateways
Do you believe that anyone will understand from these two statements what your network looks like?
If you expect any qualified reply, you should first describe your network scenario in more detail.
if make a traceroute from ip 1.2.1.4 to 1.2.5.1 then go the way every over the gateyway from ISP
Hm ...

I suppose, anybody else but me knows where (which interfaces of what routers in your network) addresses 1.2.1.4 and 1.2.5.1 are defined?
PT