Cabletron Systems CyberSWITCH CSX400 Installation Manual

Also see for CyberSWITCH CSX400: Setup guide Configuration guide User guide User guide User guide

Contents

CSX400 Firmware SupportCyberSWITCH CSX400 and CSX400-DC Installation Guide2-7DHCP and NATThe Dynamic Host Configuration Protocol (DHCP) and Network Address Translation (NAT)method eliminates the expense of purchasing limited public IP addresses for each client on a localnetwork, and the need to re-configure a client if it is moved to a different network.The CSX400 acts as a DHCP server that allows individual clients (PCs, network equipment) totake turns using a range of private IP addresses (often referred to as local IP addresses), andprovides optional secondary setup features for these clients on a per-port basis. The CSX400distributes these addresses dynamically assigning a local IP address to an individual client from arange of 253 available addresses in its table on a first-come-first-served basis. This local IP addressis then “leased” for a predetermined amount of time, which is configured for the particular port.Each Ethernet port provides DHCP services for one Class C subnet and secondary setup featuresfor individual clients that support the use of a default gateway, domain name and WINs server.On the Wide Area Network (WAN) side, the Network Address Translation (NAT) routing methodis used to enable clients assigned with local IP addresses to use the public IP address(es) of theCSX400 WAN interface(s) to access the WAN.The NAT method allows several DHCP clients on a sub network to connect to WAN clients byallowing the DHCP clients to share a single public IP address. When the CSX400 uses NAT, theNAT method modifies the IP headers and addresses, and the selected fields in upper layer protocolheaders. This is done to replace the hidden local IP addresses from the sub network with one ormore public InterNic assigned IP addresses that can be sent over the outside network on theCSX400 WAN interfaces. Once the CSX400 is assigned at least one public IP address, over 250 IPclients can share this address simultaneously using NAT. This public IP address is assignedstatically by the Internet Service Provider (ISP).NOTEA private or “local” network is referred to as a sub network that is using private or“local” IP addresses. An “outside” network refers to a Wide Area Network (WAN)commonly known as an Internet, an intranet is an “Internet” in use on a facility orcampus where registered public IP addresses are required.