W4-Dynamic Networking

In this module we look into advanced networking. We explore the following -

  • DHCP (Dynamic Host Configuration Protocol)

  • DHCP Configuration

  • DHCP Operations

  • Superscopes

  • DHCP troubleshooting

  • Authorisation

DHCP

Dynamic Host Configuration Protocol (DHCP) reduces network complexity and administration.

DHCP Clients:

  • automatically obtain network config from a DHCP server.

  • use UDP port 67/68

  • uses network braodcasts on local subnet FF:FF:FF:FF:FF

Address Allocation

Dynamic IP configuration - allocate "lease" IP address from a 'pool' (called 'scopes' in Windows) of addresses

  • "lease" is for specific adapter MAC & for specific length of time.

Can also "reserve" an IP address for a specific hosts

      • Good for servers, printers, hosts

DHCP Operations

Source: UTS FEIT Network Servers lecture slide

Reply with DHCPRELEASE when finished

DHCP Client

  1. broadcast DHCPDISCOVER UDP packet on local subnet

  2. Chooses lease & broadcasts DHCPREQUEST packet

  3. Can also reply with DHCPDECLINE if duplicate

DHCP Server

  1. Broadcast DHCPOFFER with lease info

  2. Select server replies with DHCPACK, DHCPNAK

Source: UTS FEIT Network Servers lecture slide

DHCP Scopes

DHCP Scope is rangae of IP addresses for leasing.

DHCP Reservation

Fixed IP addresses for specific DHCP client is called DHCP Reservation.

Standard DHCP Operations


Required:

  1. subnet,

  2. default router,

  3. domain name server and optional: log server,

  4. hostname,

  5. requested ipaddress,

  6. TFTP server,

  7. lease time, etc.

Packages and daemon: dhcp-server(previous: dhcp), dhclient and dhcpd

yum install dhcp-server #install

rpm –qc dhcp-server #check configurations

Global options: /etc/dhcp/dhcpd.conf

Example file: /usr/share/doc/dhcp-server/dhcpd.conf.example

/var/lib/dhcpd/dhcpd.leases # do not change

# option definitions common to all supported networks...

option domain-name "example.org";

option domain-name-servers ns1.example.org, ns2.example.org, 8.8.8.8;


default-lease-time 600;

max-lease-time 7200;

How to set

Hostname: /etc/hostname

hostnamectl set-hostname myhostname.mydomain

‘mydomain’ will be added into /etc/resolv.conf

Network Configuration - Change ifcfg file

Source: UTS FEIT Network Servers lecture slide