Preventing DHCP from allocating IPs

["Sarbjit Singh Gill" <ssgill () gilltechnologies com>]

Greetings all,

How do i prevent a client from getting an IP from my DHCP in an Ethernet
network. I know i could reserve IPs for all other clients and nobody gets an
IP unless reserved earlier, but i have hundreds of clients. I frequently
have visitors who need to plug in their laptops into the network and i have
visitors who are not allowed to plug in their laptops into the network and
get IPs. I do not want these visitors who are not allowed to access the
network to get an IP and start accessing internet through my network.

What about in a wireless environment. How do i prevent it in a similar
capacity.

Kind Regards
Gill