| This chapter, in combination with the Layer 2 firewalling chapter, should leave you equipped with a better toolbox, as it were, for dealing with protocols such as DHCP that span Layers 2 and 3. As the perl motto goes, "There's more than one way to do it," and hopefully this chapter has demonstrated this axiom. Define the Problem: What is happening, and whom is it affecting? For example, DNS lookups are failing. This manifests as some web browsers reporting that a site is not available. Gather Facts: Did anything change? Is this a DNS lookup issue? Are other systems on the internal network available that might indicate that this is a broader network outage? Don't forget to take a look with your sniffer! Define the End State: Now that you know what the symptoms and the facts are, what are you trying to accomplish? Restoring DNS or DHCP service? Develop Possible Solutions and Create an Action Plan: You know what the problems could be and whom they affect. Rough out your action plans and who should be involved. Analyze and Compare Possible Solutions: How long will it take to implement your plan, and will it solve the problem in the most efficient way? For example, it might be that your problem is that you had been using an upstream DNS server for internal DNS. When the outbound network is overloaded, DNS lookups fail frequently. You've determined you need an internal DNShow long will it take you to deploy that and, in turn, reconfigure systems to use it? What is the cost in time and money, and will it break anything else? Select and Implement the Solution: Make your plan and implement your solution. DNS and DHCP changes on a live network can lead to some pretty hefty outages, so make sure you've got your bases covered in terms of back-up plans. Don't forget to notify your users and your Helpdesk! Critically Analyze Solution for Effectiveness: After implemented, measure the effectiveness. Especially with DHCP or DNS changes, your best bet is to test this from multiple locations. Last but not least, after it's verified, don't forget to document your changes in some way.
|
