I am using following command in single user mod
->ufsdump 0f / 192.xx.xx.xx:/D/ufsdump.
#1 Your arguments are backward. With the options '0f', the next argument needs to be the device you are dumping to, not the device you are backing up. So the order is wrong
#2 192.xx.xx.xx:/D/ufsdump isn't a valid filename (at least not for you). You must first mount the remote filesystem to a spot on your local filesystem. Then you send the data to a file within that mount.