User manual

SM User Manual January 2004
Software Release 4.1
4.8.1 NAT
NAT isolates the SMs from the Internet. This both enhances SM security and obviates the need for
a special assignment scheme of IP addresses that identify the SMs. Where NAT is active, the SM
serves as a Layer 3 switch. (By contrast, where NAT is not active, the SM serves as a Layer 2
bridge.)
In the Canopy system, NAT supports HTTP, ICMP (Internet Control Message Protocols), and FTP
(File Transfer Protocol), but does not support IPsec (IP Secure).
4.8.2 DHCP
DHCP enables a device to be assigned a new IP address and TCP/IP parameters, including a
default gateway, whenever the device reboots. Thus DHCP reduces configuration time, conserves
IP addresses, and allows modules to be moved to a different network within the Canopy system.
In conjunction with the NAT features, each SM provides
• a DHCP server that assigns IP addresses to computers connected to the SM by
Ethernet protocol.
• a DHCP client that receives an IP address for the SM from a network DHCP server.
4.8.3 NAT Disabled
The NAT Disabled implementation is illustrated in Figure 12.
Figure 12: NAT Disabled implementation
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