Looking Out for Cisco ip helper Related Issues

Published: 05 September 2015
on channel: The Technology Firm

2,500

Looking Out for ip helper Related Issues
I always seem to get involved or end up in network clean ups. ‘Clean ups’ can involve physical equipment removal but also includes equipment configuration validation and optimization.
In this video I cover the typical Cisco ip helper-address command and how it can affect hosts. I would like to point out that 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) that has cause some pretty weird issues. With this specific topic, there are a few alternatives you can use to optimize this configuration from blocking unwanted protocols with an access control list, using the no ip forward-protocol udp, service command, dhcp relay and those are just off the top of my head.
The key here is that I used Wireshark to simply capture some packets of a Microsoft computer broadcasting its typical protocols and how the network equipment reacts 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 behaves before you have an issue.
I always sarcastically say to 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 what difference my changes make.

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