Router or the device gets dropped form the active clients list in the Router after 20 seconds

[videobruce]

A replacement CCTV DVR just drops the connection with the Router after 20-30 seconds after rebooting. It's done it 4 or 5 times. And the connection never returns. The activity LED's on the Ethernet port on the DVR both show active (and I have changed the cable).
The question is; is there anyway that a Router would reject or 'time out' a active device either with a static IP or a DHCP address?? Or for that matter the device itself? There are no conflicts that I know of, this isn't a huge Network, usually 5 or 6 devices active at a time.
Router is a TP Link C7 v4 running dd-wrt if that matters (and yes I have been to their forum).

Any ideas here??

 

[EarthDog]

Bad DVR is what comes to mind initially....

 

[Janus67]

If you run a persistent ping to the device does it still drop?

Tried a different router port?

I'm with ED that it seems like a bad dvr/nic. Do you have a web interface for the DVR to look at logs or anything?

 

[don256us]

I like the idea of going into a command prompt and entering: ping <IP> -t. Watch it for a few minutes to see what happens. Trying a different port is also a good idea.

When did this start happening? How old is this CCTV DVR? Did it work before? Is it new?

dd-wrt was a great router OS when I used it years ago. I don't know much about it now.