Foundry Networks Switch and Router Installation And Configuration Manual page 821

Network Address Translation
Layer 2 Switch Commands
The following commands access the configuration level of the CLI on the Foundry FastIron Workgroup Layer 2
Switch, then configure an IP address and specify the default gateway. The Layer 2 Switch connects the private
address clients to the Layer 3 Switch in Figure 20.2. The default gateway is the Layer 3 Switch's IP interface with
the Layer 2 Switch.
FastIron> en
FastIron# configure terminal
FastIron(config)# ip address 10.10.10.49/26
FastIron(config)# ip default-gateway 10.10.10.50/26
The following command saves the configuration to the Layer 2 Switch's startup-config file on flash memory. The
Layer 2 Switch applies the configuration information as soon as you enter it into the CLI. Saving the changes to
the startup-config file ensures that the changes are reinstated following a system reload.
FastIron(config)# write memory
Layer 3 Switch Commands
The following commands access the configuration level of the CLI.
BigIron> en
BigIron# configure terminal
BigIron(config)#
The following command configures an ACL to identify the range of private addresses for which you want to
provide NAT services. This ACL identifies the private address range as 10.10.10.0 – 10.10.10.255.
BigIron(config)# access-list 9 permit 10.10.10.0 0.0.0.255
NOTE: The format of the network mask for an ACL uses zeroes to indicate a value that must match, and ones
(255 in decimal) as a wildcard. In this case, 0.0.0.255 means the first three parts of the IP address must match
exactly, but the fourth part can have any value.
The following command configures the NAT address pool. The Layer 3 Switch translates a client's address from
the private network to an address from this pool when the client sends traffic to a public network, in this case a
network located somewhere on the Internet.
BigIron(config)# ip nat pool np1 63.251.295.47 63.251.295.48 netmask 255.255.255.192
This command configures a pool named "np1", and adds public address range 63.251.295.47/26 –
63.251.295.48/26 to the pool. Generally, a pool contains more than two addresses, but this pool is small so that
this configuration can also demonstrate the Port Address Translation feature.
The following command associates the range of private addresses identified by the ACL with the pool, and in this
case also enables the Port Address Translation feature. Port Address Translation allows you to use an address
pool that contains fewer addresses than the number of NAT clients in the private network.
BigIron(config)# ip nat inside source list 9 pool np1 overload
The inside source list 9 portion of the command identifies the range of source addresses. The value "9" is the
number of the ACL configured above. The pool np1 portion of the command identifies the IP address pool
configured above. The overload parameter enables Port Address Translation. When this feature is enabled,
NAT associates a TCP or UDP port number with the public address for a client. In this case, there are four clients
but only two addresses in the pool. Port Address Translation allows NAT to provide translation addresses for all
four clients. When two translation clients have the same public IP address, the software can still distinguish
between the clients because each client has a unique TCP or UDP port number.
The following command configures a static default route to the Internet access router. The Layer 3 Switch uses
this route for traffic that is addressed to a destination for which the IP route table does not have an explicit route.
Typically, the IP route table does not have explicit routes to all destination networks on the Internet.
BigIron(config)# ip route 0.0.0.0 0.0.0.0 63.251.295.1
December 2000 20 - 15