DHCP Failover on GNU/Linux

Hannah is a GNU/Linux System Administrator at Red Hat. She is researching setting up DHCP failover on Server A and Server B. Please generate an essay for Hannah's consumption that answers the following questions. Please note that Hannah prefers "Free Software" to "open-source".

  1. What is DHCP and what is DHCP failover?
  2. What is the history of DHCP and DHCP failover?
  3. How would Hannah implement DHCP failover on RHEL Servers A and B using only Free Software? Please list and fully explain all commands that she will have to execute.
  4. What are the strengths and weaknesses of DHCP failover?

DHCP and DHCP Failover: An Essay for Hannah, the GNU/Linux System Administrator


Dynamic Host Configuration Protocol (DHCP) is an essential component of modern network management. It allows for the automated assignment of IP addresses and other network configuration parameters to devices, simplifying network administration. DHCP failover is a mechanism designed to ensure DHCP service continuity in the event of server downtime, be it due to maintenance, failure, or other service disruptions. As a staunch advocate of Free Software, understanding the history, implementation, and analysis of DHCP and its failover capabilities within Red Hat Enterprise Linux (RHEL) environments using Free Software tools is critical.

Understanding DHCP and its Purpose

DHCP stands out in network management by allowing clients to receive IP configurations automatically. These configurations often include IP address, subnet mask, default gateway, and DNS server information. DHCP's role is indispensable in large networks where manual assignment would be impractical and error-prone.

The Concept of DHCP Failover

Failover refers to the ability of a secondary service or server to take over when the primary is unavailable. In DHCP failover configurations, two servers share the responsibility for leasing IP addresses and configuration data to clients. This sharing can either be in a load-balanced fashion, where both servers handle requests simultaneously, or in a standby mode, where the secondary server only responds if the primary server is down.

Historical Backdrop of DHCP and DHCP Failover

The DHCP protocol, defined in RFC 2131, evolved from the Bootstrap Protocol (BOOTP). It became a standard in the mid-1990s, responding to the growing complexity of networks and the need for more dynamic IP address management. DHCP failover was later formalized in RFC 2131 as networks grew in size and complexity, requiring higher availability.

Implementing DHCP Failover on RHEL Servers Using Free Software

For Hannah's project on RHEL, she would need to use the ISC DHCP Server, a Free Software implementation of the DHCP protocol. The following are the steps and commands she would need to execute to set up DHCP failover on two RHEL servers:

  1. Installation of the DHCP Package

    On both Server A and Server B, she would install the ISC DHCP server package using dnf, RHEL's package manager:

    sudo dnf install dhcp-server
  2. Configuration of the Primary DHCP Server (Server A)

    Hannah would modify the DHCP configuration file located at /etc/dhcp/dhcpd.conf:

    sudo vi /etc/dhcp/dhcpd.conf

    Inside this file, she would declare a failover peer:

    failover peer "dhcp-failover" { primary; address; port 647; peer address; peer port 647; max-response-delay 30; max-unacked-updates 10; load balance max seconds 3; mclt 3600; split 128; }

    Then, she'd define a subnet and associate it with the failover peer:

    subnet netmask { option routers; option domain-name-servers; pool { failover peer "dhcp-failover"; range; } }
  3. Configuration of the Secondary DHCP Server (Server B)

    After configuring the primary server, Hannah would repeat the process on Server B, this time specifying it as the secondary in the failover pair:

    failover peer "dhcp-failover" { secondary; address; port 647; peer address; peer port 647; max-response-delay 30; max-unacked-updates 10; load balance max seconds 3; }
  4. Starting and Enabling the DHCP Service

    On both servers, she would enable and start the DHCP service:

    sudo systemctl enable dhcpd sudo systemctl start dhcpd
  5. Monitoring the DHCP Failover Status

    To ensure that the failover is set up correctly, Hannah can monitor the status and logs of the DHCP service:

    sudo systemctl status dhcpd sudo tail -f /var/log/messages | grep dhcpd

Strengths and Weaknesses of DHCP Failover

The strengths of DHCP failover are clear: increased reliability, improved network uptime, and the seamless distribution of network configuration parameters even in the event of server failure. It promotes uninterrupted network service, which is vital for businesses and organizations that rely on constant connectivity.

However, there are weaknesses to consider. DHCP failover systems can become complex to set up and manage, especially when dealing with large and dynamic networks. The synchronization of lease databases between the primary and secondary servers can also introduce overhead and potential for conflicts. Moreover, if not configured correctly, both servers could end up distributing overlapping IP addresses, causing network issues.


For Hannah, and indeed any GNU/Linux system administrator at Red Hat or elsewhere, establishing DHCP failover is a task that merges network reliability with the ideology of Free Software. By leveraging the ISC DHCP Server, a Free Software solution, Hannah can ensure that her RHEL servers provide continuous DHCP service, aligning with the technical and philosophical standards expected by her and the wider Free Software community.

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