Slide 24 of 27
Increasingly, residential and SOHO sites do not have a single system connected to the Internet but a LAN that they want connected to the Internet. But since these are "residential" services, the site is only provided with a single IP address, and only temporarily at that.
A new set of products has emerged to meet the requirements of home/SOHO networks, as shown in the slide. In this example, the site has been assigned the public IP address 184.108.40.206. But instead of connecting the ADSL or cable modem directly to a single PC, it is attached to small router that looks like a Dynamic Host Configuration Protocol (DHCP) client to the network and acts like a firewall to the LAN. In this case, we will use the RFC 1918 private IP network number 192.168.50.0; the router, then, has to be able to perform Network Address Translation (NAT) to map the private host addresses to the single public address. The router might also be able to act like a DHCP server for the LAN and may even include an embedded LAN hub or switch.