NAT and DHCP
By default, the AirPort acts as both a NAT
server and a DHCP server for your wireless clients. DHCP service is controlled by the
DHCP Functions tab. To turn DHCP on, check the
Provide DHCP address delivery to wireless hosts
box. You can specify the range of IPs to issue; by
default, the AirPort hands out leases between
10.0.1.2 and 10.0.1.50. You
can also set a lease time here. The lease time specifies the lifetime
(in seconds) of an issued IP address. After this timer expires, the
client reconnects to the DHCP server and requests another lease. The
default of 0 (or unlimited) is probably fine for
most installations, but you may want to set it shorter if you have a
large number of clients trying to connect to your AirPort.
If you don't have another DHCP server on your
network, the AirPort can provide service for your wired hosts as
well. Check the Distribute addresses on Ethernet port,
too box if you want this functionality.
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Check this box only if you don't have another DHCP
server on your network! More than one DHCP server on the same subnet
is a bad thing, and will bring the wrath of the
sysadmin down upon you. Watching two DHCP servers duke out who gets
to serve leases may be fun in your spare time, but can take down an
entire network, and leave you wondering where your job went. What
were you doing connecting unauthorized gear to the company network,
anyway?
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If you have more than one AirPort on the same wired network, make
sure that you enable DHCP to the wire on only one of them and, again,
only if you don't already have a DHCP server.
NAT is very handy if you don't have many IP
addresses to spare (and these days, few people do). It also gives
your wireless clients some protection from the wired network, as it
acts as an effective one-way firewall (see Chapter 3 for the full story of NAT and DHCP). In the
Configurator, NAT is set up in the Bridging
Functions tab. To enable NAT, click the Provide
network address translation (NAT) radio button. You can
either specify your own private address and netmask, or leave the
default (10.0.1.1 / 255.255.255.0).
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