Cabletron Systems CSX200 CyberSWITCH, User Manual

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About the CSX200
CSX200 Family User’s Guide 11
The NAT method allows several DHCP clients on a sub network to connect to WAN clients by
allowing the DHCP clients to share a single public IP address. When the CSX200 uses NAT, the
NAT method modifies the IP headers and addresses, and the selected fields in upper layer protocol
headers. This is done to replace the hidden local IP addresses from the sub network with one or
more public InterNic assigned IP addresses that can be sent over the outside network on the
CSX400 WAN interfaces. Once the CSX200 is assigned at least one public IP address, over 250 IP
clients can share this address simultaneously using NAT. This public IP address is assigned
statically 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 traffic
over point-to-point connections. It is suitable for both high-speed synchronous ports as well as
lower speed asynchronous dial-up ports. With this protocol, options such as security and network
protocols can be negotiated over the connection.
The STAC Electronics Stacker LZS Compression Protocol is supported over PPP providing up to
4:1 data compression.
PAP and CHAP Security
The CSX200 supports the Password Authentication Protocol (PAP) and Challenge Handshake
Authentication 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 the
authenticator checks the peer’s password against the configured remote peer’s password and
returns acknowledgment.
CHAP is more secure than PAP as unencrypted passwords are not sent across the network. CHAP
uses a 3-way handshake and supports full or half-duplex operation.
NOTE
A 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 or
campus where registered public IP addresses are required.