User Manual

Enterasys X-Pedition User Reference Manual 327
Configuring NAT
The XP allows you to create the following NAT address bindings:
• 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 XP:
1. Setting the NAT interfaces to be “inside” or “outside.”
2. Setting the NAT rules (static or dynamic).
Note: NAT interfaces do not currently support VRRP.
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.
Note: The XP will display interface names up to 32 characters in length.
Define an interface as inside or
outside for NAT.
nat set interface <InterfaceName> inside|outside