Chapter 38. Network Addresses

Objective

• Know the difference between IPv4 and IPv6 addresses
• Get, set and change the hostname, based on the system we are using

IP Addresses

Are node's addresses used globally and uniquely across the internet. They are registered through ISPs (Internet Service Providers). It is basically a number that indentifies a node in a network.

IPv4

Its a 32 bit address, composed of 4 octets, for example 

​148.114.252.10

​IPv6

Its a 128 bit address, composed of 8 16-bit octet pairs, for example

​2003:0db5:6122:0000:1f4f:0000:5529:fe23

​In either case, a set of reserved addresses is also included.

IPv4 Address Types

IPv4 address types include

• Unicast
  • An address associated with a specific host. It might be something like 140.211.169.4 or 64.254.248.193
• Network
  • An address whose host partition is set to all binary zeroes, like 192.168.1.0
• Broadcast
  • An address to which each member of a particular network will listen. It will have the host portion set to all 1 bits, for example
    • 172.16.255.255
    • 148.114.255.255
    • 192.168.1.255
• Multicast
  • An address to which appropriately configured nodes will listen. The address 224.0.0.2 is an example of a multicast address. Only nodes specifically configured to pay attention to a specific multicast address will interpret packets for that multicast group

Special Addresses

• 127.x.x.x
  • Reserved for loopback (local system) interface, Generally 127.0.0.1
• 0.0.0.0
  • Used by systems that do not yet know their own address. Protocols like DHCP and BOOTP use this address when attempting to communicate with a server
• 255.255.255.255
  • Generic broadcast private address, reserved for internal use. These addresses are never assigned or registered to anyone. Generally they are not routable

IPv6 Address Types

• Unicast
  • A package is delivered to one interface
    • Link local
    • Global
    • Reserved for documentation
• Multicast
  • A packet is delivered to multiple interfaces
• Anycast
  • A packet is delivered to the nearest of multiple interfaces (in terms of routing distance)
• IPv4-mapped
  • An IPv4 address mapped to IPv6. For example ::FFF:a.b.c.d/96

In addition IPv6 has some special types of addresses such as loopback, which is assigned to the lo interface, as ::1/128

IPv4 Address Classes

Netmasks

The netmask is used to determine how much of the address is used to determine the network portion and how much for the host portion. Its also used to determine network and broadcast addresses.

Address Classes and Netmasks

• Class A
  • Use 8 bits for the network portion of the address and 24 bits for the host portion of the address
• Class B
  • Use 16 bits for the network and 16 for the host
• Class C
  • Use 24 bits for the network and 8 for the host
• Class D
  • Are used for multicasting
• Class E 
  • Are not used

The network address is obtained by anding (logical AND) the IP address with the netmask. We are interested in the network address because they define a local network, all nodes within the same network can see each other.

Example

172.16.2.17     ip address
$255.255.0.0   netmask
------------------
172.6.0.0         network address

Hostname

Its a label used to identify a node in the network

Note: a FQDN = Fully Qualified Domain Name 

is a mixture of the domain and the hostname

Example

alejandro.asys.com
Domain : asys.com
Hostname: alejandro

​Getting and Setting the Hostname

Get the hostname

$ hostname

Change the hostname to "andres" in a non persisten fashion

$ sudo hostname andres

Change the hostname in a persisten fashion we need to change the name at

/etc/hostname

or for Red Hat systems

/etc/sysconfig/network

or using the tool

$ hostnamectl --help

Changing the hostname is as simple as

$ sudo hostnamectl set-hostname MYPC