About the CSX40012 CSX400 and CSX400-DC User’s GuideThe 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).Point-to-Point Protocol (PPP)PPP is a data link layer industry standard WAN protocol for transferring multi-protocol data trafficover point-to-point connections. It is suitable for both high-speed synchronous ports as well aslower speed asynchronous dial-up ports. With this protocol, options such as security and networkprotocols can be negotiated over the connection.This device supports synchronous PPP over the ISDN port. In Single Link Mode, PPP uses oneISDN B channel for data transmission. PPP runs over each ISDN B channel for two separateconversations (split B-channel). In Multi-Link Protocol Mode, PPP simultaneously sends andreceives data over two ISDN B-channels on the same connection to optimize bandwidth usage.The STAC Electronics Stacker LZS Compression Protocol is supported over PPP providing up to4:1 data compression.PAP and CHAP SecurityThe CSX400 supports the Password Authentication Protocol (PAP) and Challenge HandshakeAuthentication Protocol (CHAP) under PPP.PAP provides verification of passwords between devices using a 2-way handshake. One device(peer) sends the system name and password to the other device (authenticator). Then theauthenticator checks the peer’s password against the configured remote peer’s password andreturns acknowledgment.CHAP is more secure than PAP as unencrypted passwords are not sent across the network. CHAPuses a 3-way handshake and supports full or half-duplex operation.
