Best Practices for DHCP Logging

As an IT and security auditor, I have seen the importance of DHCP logging in, ensuring network security, and troubleshooting network issues. Here are the best practices for DHCP logging that every organization should follow:


1. Enable DHCP Logging: DHCP logging should be turned on to record every event that occurs in the DHCP server. The logs should include information such as the time of the event, the IP address assigned, and the client’s MAC address.

2. Store DHCP Logs Securely: DHCP logs are sensitive information that should be stored in a secure location. Access to the logs should be restricted to authorized personnel only.

3. Use a Centralized Logging Solution: To manage DHCP logs, organizations should use a centralized logging solution that can handle logs from multiple DHCP servers. This makes monitoring logs, analyzing data, and detecting potential security threats easier.

4. Regularly Review DHCP Logs: Regularly reviewing DHCP logs can help detect and prevent unauthorized activities on the network. IT and security auditors should review logs to identify suspicious behavior, such as unauthorized IP and MAC addresses.

5. Analyze DHCP Logs for Network Performance Issues: DHCP logs can also help identify network performance issues. By reviewing logs, IT teams can identify IP address conflicts, subnet mask issues, and other network performance problems.

6. Monitor DHCP Lease Expiration: DHCP lease expiration is vital to ensure IP addresses are not allotted to unauthorized devices. DHCP logs can help to monitor lease expiration and to deactivate the leases of non-authorized devices.

7. Implement Alerting: IT and security audit teams should implement alerting options to ensure network security. By setting up alert mechanisms, they can be notified of suspicious activities such as unauthorized devices connecting to the network or DHCP problems.

8. Maintain DHCP Logs Retention Policy: An effective DHCP logs retention policy should be defined to ensure logs are saved for an appropriate period. This policy will help to provide historical audit trails and to comply with data protection laws.


Following these DHCP logging best practices will help ensure the network’s security and stability while simplifying the troubleshooting of any network issues.

A Couple of Interesting Developments

First, a couple of new tools are available specifically geared at cracking Oracle 11g password hashes. These are specifically aimed at attacking the newest features that 11g introduces to better protect the passwords. They also have some short cuts for those folks still making the old style DES passwords available (likely for backwards compatibility with older apps or uses). Essentially, these new mechanisms are slower than old hash attacks, but are still effective. In today’s world of computational power and bot-net distributed password cracking capability, it is pretty darn safe to assume that if the attacker can get the hash – they can get the password.

Another issue that is likely to be an annoyance for some folks is that a new remote Denial of Service attack has been identified in Ubuntu 6.06 DHCP server. While the attacker can’t really gain access to the system using it, they can replace the dead DHCP server with their own, which could include malicious entries and other annoyances. This DHCP server is popular in many cyber cafes I have visited – particularly outside of the US. Just another reminder that you have to pay attention to network connectivity. It might seem like ubiquitous wireless access is a boon, but without the capability to trust the network you use, you have little reason to trust the content you receive!  — Just a reminder!