Birmingham mumbai

[
 256 
]
We also include 
/24
 to declare that the IP address is part of a 24-bit 
subnet
, which is 
fairly standard unless your network administrator has set up a larger scope. A 
/24
 
network is the same as a Class C network, if that's more familiar to you. This also 
takes care of the subnet mask, which we don't need here since 
/24
 implies the same 
subnet mask as 
255.255.255.0
 (if you're more familiar with the classful style, which 
shows the subnet mask in the same format as an IP address). We will discuss subnets 
in 
Chapter 11
, 
Setting Up Network Services
, however, a full walk-through of subnetting 
and the TCP/IP protocol is beyond the scope of this book, so we won't worry too 
much about that value for now.
Moving on, we also set up the gateway:
      gateway4: 192.168.100.1
When it comes to networking, the gateway refers to the "next hop," which is basically 
the IP address that outbound connections are routed through. This value will need 
to match the actual default gateway address on your network, which is quite often 
the same as the IP address with the last portion being 
.1
. If in doubt, you can check 
the IP address assignment of another device on the same network you're joining the 
Ubuntu server to, which would be the same.
The last section allows us to configure the DNS server that our server will use to look 
up external domain names:
      nameservers:
        addresses: [192.168.100.1, 192.168.100.2]
The example configuration is just that, an example—all the values must match 
whatever is appropriate for your network. Often, the DNS server IP address 
will be the same as the gateway address, but that's not always true. Sometimes a 
network administrator will have a custom IP scheme for DNS servers. I also added 
a secondary DNS server in the example, 
192.168.100.2
, but you can remove the 
second IP address if that's not necessary.
Once you've ensured that the values in the file are appropriate, we'll need to apply 
and test these changes:
•  If you are using a virtual machine, you may want to make the changes from 
the virtual machine console.
•  If you're updating a physical machine, you may want to have a display and 
keyboard attached.
•  Although we discuss OpenSSH later in this chapter, if you're already aware 
of how to connect to a server via OpenSSH, you probably won't want to 
change network configuration over OpenSSH, since as soon as you activate 
these changes your connection will drop.

---

Chapter 10