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Assigning static IP addresses
With servers, it's very 
important that your IP addresses remain fixed and do not 
change for any reason. If an IP address does change (such as a dynamic lease with 
no reservation), your users will experience an outage, services will fail, or entire sites 
may become unavailable. When you install Ubuntu Server, it will grab a dynamically 
assigned lease from your DHCP server, but after you configure the server the way 
you want it, it's important to set a permanent IP address right away before it's 
considered production-ready. One exception to this rule is an Ubuntu-based VPS. 
Cloud providers that bill you for these servers will have an automatic system in 
place to declare an IP address for your new VPS, and will already have it configured 
to remain in place. But in the case of virtual or physical servers you manage yourself, 
you'll start off with a dynamic address, unless you've already configured a static IP 
address during installation.
In most cases, you'll have an IP address scheme in place at your office or 
organization, which will outline a range of IP addresses that are available for use 
with static assignments. If you don't have such a scheme, it's important to create one, 
so you will have less work to do later when you bring more servers online. We'll 
talk about setting up a DHCP server and IP address scheme in 
Chapter 11
, 
Setting 
Up Network Services
, but for now, I'll give you a few quick tips. Your DHCP server 
will typically have a range of IP addresses that will be automatically assigned to 
any host that requests an assignment. When setting up a static IP on a server, you'll 
want to make sure that the IP address that you choose is outside of the range that 
your DHCP server assigns so you don't end up with a duplicate IP on your network. 
For example, if your DHCP server assigns IPs ranging from 
10.10.10.100
 through 
10.10.10.150
, you'll want to use an IP address 
not
 included within that range for 
your servers.
There are two ways of assigning a fixed address to a network host, including your 
servers. The first is by using a static IP assignment, as I've already mentioned. With 
that method, you'll arbitrarily grab an IP address that's not being used by anything, 
and then configure your Ubuntu Server to use that address. In that case, your server 
is never requesting an IP address from your network's DHCP server. It simply uses 
whatever you assign it. This is the method I'll be going over in this section.
The other way of assigning a fixed address to a server is by using a static lease. This 
is also known as a