Cabletron Systems SmartSwitch manual Configuring NAT, Setting Inside and Outside Interfaces

Chapter 14: Network Address Translation Configuration Guide

•Static, one-to-one binding of inside, local address or address pool to outside, global address or address pool. A static address binding does not expire until the command that defines the binding is negated. IP addresses defined for static bindings cannot be reassigned. For static address bindings, PAT allows TCP or UDP port numbers to be translated along with the IP addresses.

•Dynamic binding between an address from a pool of local addresses to an address from a pool of outside addresses. With dynamic address binding, you define local and global address pools from which the addresses bindings can be made. IP addresses defined for dynamic binding are reassigned whenever they become free. For dynamic address bindings, PAT allows port address translation if no addresses are available from the global address pool. PAT allows port address translation for each address in the global pool. The ports are dynamically assigned between the range of 1024 to 4999. Hence, you have about 4,000 ports per global IP address.

Dynamic bindings are removed automatically when the flow count goes to zero. At this point, the corresponding port (if PAT enabled) or the global IP address is freed and can be reused the next time. Although there are special cases like FTP where the flows are not installed for the control path, the binding will be removed only by the dynamic binding timeout interval.

Configuring NAT

The following are the steps in configuring NAT on the SSR:

1.Setting the NAT interfaces to be “inside” or “outside.”

2.Setting the NAT rules (static or dynamic).

Setting Inside and Outside Interfaces

When NAT is enabled, address translation is only applied to those interfaces which are defined to NAT as “inside” or “outside” interfaces. NAT only translates packets that arrive on a defined inside or outside interface.

To specify an interface as inside (local) or outside (global), enter the following command in Configure mode.

Define an interface as inside or outside for NAT.

nat set interface <InterfaceName> insideoutside

224 SmartSwitch Router User Reference Manual