Studio Press

Networks are naturally susceptible to failures because they contain many components and are affected by the configuration of every component. Where, exactly, is your network? In the switch? The drop cables? Bounded by all of the network interface cards in your systems? Any of those physical components can break, resulting in network outages or, more maddeningly, intermittent network failures.

Networks are also affected by configuration problems. Incorrect routing information, duplicate hostnames or IP addresses, and machines that misinterpret broadcast addresses can lead to misdirected packets. You’ll also have to deal with redundancy in network connections, as you may have several routers connecting networks at multiple points. When that redundancy is broken, or its configuration is misrepresented, the network appears to be down.

When a network that you trust and love is connected to an untrusted or unmanaged network, you run the risk of being subject to a denial-of-service attack or a network penetration attempt from one of those networks. These types of attacks happen within well-run networks as well. Security mogul Bill Cheswick asks the attendees at his talks if they leave their wallets out in the open in their offices. Nary a hand goes up. Then he asks how many leave unprotected network access points like twisted-pair wall jacks in open offices, and you see the tentative hands raised. Access to the network is valuable and has to be protected while still allowing user activity to proceed without onerous overhead.

Finally, networks use a variety of core services or basic information services that we lump into the network fabric. Naming systems like NIS or DNS, security and authentication servers, or host configuration servers for hosts requiring DHCP to boot and join a network will bring down a network if they are not functioning or are giving out wrong answers.

File and Print Server Failures

When file and print server fail, clients will hang or experience timeouts. A timeout can mean that a print job or a file request fails. The timeout can also lead to wrong answers or data corruption. For example, using Network File Systems (NFS) soft mounts, a write operation that times out will not be repeated. This can lead to holes in data files that will only be detected when the file is read.

Source: http://www.web-articles.info/e/a/title/File-and-Print-Server-Failures/