What are the methods of separating network spaces in a LAN?

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http://serverfault.com – Please detail me the methods. My thoughts: put the servers in separate (sub)networks the servers are forced to go through the firewall but no NAT is required assign more IP addresses to the internal interface of the server choosing gateway addresses from the clients and servers IP address ranges split DNS Netfilter/{iptables, ipset} could be heavily involved, I'm talking about Linux servers. See for example: Destination NAT Onto the Same Network from internal clients Please do not explain what is NAT or DNS. This is a theoretical question, but my poor English knowledge prevent me to (HowTos)