About the CSX400CSX400 and CSX400-DC User’s Guide 11HDLCCabletron Systems has provided the High-level Data Link Control (HDLC) protocol which is usedin conjunction with the Inverse Multiplexing (IMUX) feature and the WPIM-HDSL to conserve auser’s WAN bandwidth between two Cabletron Systems products, over a point-to-pointconnection. Cabletron Systems products such as the CSX400, CSX200, and HSIM-W6 must be inuse on both ends of the WAN link for these functions to work. The HDLC (RAW) protocol reducesthe amount of overhead information that needs to be contained within each data packet to direct itto its destination. This decreased packet overhead provides the IMUX and HDSL functions withmore bandwidth to transfer user data.DHCP 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.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.
