netgear routers

[#1]

When I log into my netgear router and choose the 'network devices' option I get something like
192.168.0.1          xx:xx:9A:A3:27:88        <unknown>
192.168.0.5          xx:xx:2B:70:B6:27        <unknown>
192.168.0.103    xx:xx:A9:BB:21:4B        DEVICE_1
192.168.0.100    xx:xx:A9:BB:16:1E        DEVICE_2
192.168.0.4        xx:xx:00:98:ED:A0        DEVICE_3
192.168.0.101    xx:xx:xx:B2:F4:1D        DEVICE_4
<unknown>        xx:xx:81:57:f2:7a          <unknown>
<unknown>        xx:xx:b0:c9:12:f7          <unknown>

Anyone know how to get the missing <unknown> fields to be completed?

[#2]

About the only way to get the unknows filled in is to renew the DHCP lease, and hope!
For the device names,  the unknown indicates that it wasn't told what the devices name was,  or it's forgotten.
With the missing IP address,  that's indicating that the device with that MAC address has connected to the router at some point,  but it's lease on the IP address expired and it now doesn't have one.
This allows you to identify possible intruders and block them. if desired.

[#3]

As long as you don't need the name to be passed to DNS there should not be a problem 
However, the lack of a name is usually due to the way the client formulates the DHCP request. In the past I have noticed that "names" are present for Microsoft based systems but not Linux based. For my Linux system, I have explicitly set the "DHCP client identifier" and "Hostname to send" in the global parameters for the network card. I don't have a name/MAC binding set up in the DHCP server and the client is identified by name in the server active client list.
IIRC, Linux systems may use the MAC address as the identifier.