Best Practices for Architecting DHCP Networks

DHCP

Best Practices for Architecting DHCP Networks

Size of office or branch – does the size of the branch or office warrant its own DHCP server. If the number of devices at a location is quite small, you may be able to get away with manual allocation. This can change quickly however, as the number of devices can grow quickly, especially with the advent of IP phones and wireless devices. 

Available bandwidth – if the available bandwidth is an issue, consider deploying DHCP locally. Even though DHCP traffic is considered to be light, an already overtaxed WAN connection may not be able to able to sustain the level of traffic needed to provide adequate DHCP service.

Address availability– if a device cannot get an address, it falls off the network. If your remote location does not have redundancy built into its DHCP solution, whether through their WAN connection or other devices on their network, losing connectivity with the remote server, can translate to loss of addresses. Having a backup solution in the event of connectivity loss is an important part of every disaster plan.

DHCP Failover

As with DNS, eliminating single points of failure is more of a necessity than a best practice. Single server deployments are always more susceptible to outages than solutions that take redundancy into account. If a DHCP server goes down for a long enough period of time, dynamically-configured IP devices (which are most of the current devices) eventually lose network connectivity. Redundancy in DHCP design is critical.  For maximum reliability, I recommend running DHCP Failover between two DHCP servers. While you have the option of placing both servers at the same location, for many of the same reasons discussed in the DNS section, we recommend separating the servers geographically with one server located at the local site and the second located at the main or regional headquarters. In this way, should the local server fail, DHCP services are still provided by the remote server. 

In a DHCP Failover relationship, each server is aware of any leases assigned by its peer server. This cooperating relationship keeps the address database on each server synchronized. As a result, Failover is able to provide service continuity in the event of hardware, software or network failure without the need to manually reconfigure address pools.

Conclusion

This information outlines some of the choices available to network designers implementing DHCP solutions. It offers recommendations to help secure IP networks, reduce service outages, and enhance network performance.  While there are always trade-offs to be made in any network design – particularly when budgetary constraints are factored in –designs that take best practices into account allow you to minimize the negative impact of design trade-offs as much as possible.  As IP networks continue to grow in size and complexity, and as the threats to network security evolve, we can expect best practice recommendations to keep pace, addressing the new challenges of modern, dynamic network infrastructures. 

When considering the best practices mentioned above, these notes will situate your company correctly to provide a DHCP solutions designed to meet the requirements and needs of any organization. Using the correct DHCP servers and/or appliances will provide a successful and efficient network that leverages the DHCP best practices.