Troubleshooting IP Helper Address Issues

IP helper addresses are often used to manage broadcast protocols, especially when it comes to DHCP, but be on the lookout for potential problems they can cause.

Tony Fortunato

September 10, 2015

1 Min Read
Network Computing logo

I always seem to end up involved in network "cleanups." These cleanups can involve physical equipment removal, but they also include equipment configuration validation and optimization.

In this video I cover the Cisco ip helper-address command and how it can affect hosts. This commonly used command forwards various UDP broadcast protocols to a specific device. I have actually seen IP helper addresses configured with a broadcast address (not recommended), which has caused some pretty weird issues. There are a few other alternatives you can also use to optimize this configuration from blocking unwanted protocols. Those include access control lists and using the no ip forward-protocol udp, service command, and dhcp relay.

In the video, I started with a model of my network in the software tool GNS3. Then I used Wireshark to simply capture some packets from a Microsoft computer broadcasting its typical protocols and how the network equipment reacted to it. I term these exercises "PC bootup baseline," "PC idle baseline" and, of course, "PC login baseline." I can’t stress the importance of performing these baselines to get a true picture of how your network and equipment behave before you are actually experiencing an issue.

I always sarcastically tell my clients that if you perform a baseline correctly, you will have some research to do. And in most cases, you will have some changes to make. I like using captures or anything quantitative so I can see the differences my changes make.


About the Author(s)

Tony Fortunato

Sr Network Performance Specialist

Tony Fortunato is a network performance expert who has been designing, implementing and troubleshooting networks since 1989. His company, The Technology Firm, provides clients of all sizes with services ranging from project management, network design, consulting, troubleshooting, designing custom-designed training courses, and assisting with equipment installation. Tony's experience in networking started with financial trading floor networks and ISPs, where he learned to integrate and support equipment from various vendors. Tony has taught and presented at numerous colleges and universities, public forums and private classes. He blogs frequently at NetworkDataPediaand has a popular YouTube channel.

Stay informed! Sign up to get expert advice and insight delivered direct to your inbox

You May Also Like

More Insights