the ongoing operation of your network, and should be upgraded. A new feature is needed Notice I didn't say, "A new feature is wanted." Sometimes a new feature is a necessity. I once worked on a large network with DS3s crossing the globe. We had almost 40 of them. When one bounced a few times within a few minutes, it wreaked havoc with our VoIP environment. This network supported upwards of 300 calls per second, SO bouncing links was a severe problem. The answer was IP route dampening, which was in a cutting-edge version of the code (note that this was EIGRP and not BGP, SO route dampening was not inherent in the protocol). Normally, I would never advocate using a cutting-edge release, but in this case, the feature was SO necessary to the continued successful operation of the net- work that we decided to go ahead. Luckily, the feature solved our problems without adding any new ones. A technology change If you had a T1, and now you have a DS3, you probably need to add a DS3 interface card to support the DS3. To increase performance Sometimes, companies simply outgrow their hardware. I've seen web sites go from PIX 515s, to 520s, to 525s, to Firewall Services Modules for no other rea- son than that they were exceeding the aggregate bandwidth that the devices could handle. Chapter 38: Avoiding Frustration To increase simplicity I'm a big fan of integrated CSU/DSU WICs. If you have T1s that are still using CSU/DSUs with V.35 cables, you can eliminate connection points and separate devices by integrating the CSU/DSU into the router. This is a single example, but many similar situations exist. To increase reliability If you have one firewall, adding a second firewall SO they act as a failover pair increases the reliability of the network. High availability is a good thing, and should be implemented whenever your budget allows. To lower costs If you can prove that upgrading some hardware or software will lower costs, upgrading is a viable option. An example might be collapsing a router and a switch into a single 3750 lay