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DHCP

DHCP is stateful and requires a separate server to manage and assign all addresses. If this server fails, hosts cannot connect. The host relies on the DHCPv6 server to obtain configuration information (DNS Server addresses) and maintain connections to the network. It's an old method where an administrator uses a pool of IP addresses and assigns it to a host as needed. The DHCP server handles network configuration and configures each host. There is no need to configure leases with DHCP.

DHCP Configuration

The DHCP server for IPv6 is dhcp6s with configuration file /etc/sysconfig/dhcp6s, and a client is dhcp6c with /etc/dhcp6c. A service script /etc/init.d/dhcp6s used to manage the dhcp6s server.

  • dhcpd in the /etc/rc.d/init.d directory: To start and stop DHCP server
  • dhcpd.leases in the /var/lib/dhcp directory: Contains the dynamically allocated IP addresses assigned for a given time. When leases expire, they are extended, or a new one gets generated. The lease entry specifies the IP address and the start and the end times of the lease along with the client's hostname.
  • /etc/sysconfig/dhcpd file: DHCP server arguments and options
    DHCPARGS=eth0
service dhcpd start

DHCP client dhclient – /etc/dhclient.conf: It keeps lease information on the DHCP connection in the /var/lib/dhcp/dhclient.leases file.
IPv4 server: dhcpd
Client support: dhclient

IP address allocation methods

  • Automatic: assigns a permanent IP address for a host
  • Manual: assigns IP address designated by the network administrator
  • Dynamic: DHCP server allocates IP addresses to a host on the network when needed from a pool of IP addresses and release when finished

DHCP Failover Protocol: Two DHCP servers (primary and secondary) support the same address pool, in sync, and have an identical copy of network support information for each host on the network. If one fails, the other continues to provide DHCP services for a network.

If there is no router, there are no route advertisements, then a stateful method DHCPv6 or manual configuration is used to provide the addresses.

DHCP Versions

DHCP based on BOOTP developed for diskless workstations

  • IPv4 Protocol: It has no dynamic configuration, hence more dependent on DHCP.
  • DHCPv6: IPv6 Protocol, that includes information for dynamic configuration

The DHCP server provides network configuration information to systems running client daemon connected to an IPv4 TCP/IP network, whether the Internet or an Intranet. It includes IP address, network name server, gateway and proxy addresses, and the netmask.
A network administrator manages the network configuration for all the systems on the network from the DHCP server.

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