Carefully constructing walls and moats to keep the bad guys out of our systems is an everyday task. It's equally important to build walls and moats to keep them in, should they successfully penetrate our defenses. . .
Carefully constructing walls and moats to keep the bad guys out of our systems is an everyday task. It's equally important to build walls and moats to keep them in, should they successfully penetrate our defenses.

Let's go ahead and review why filtering outbound traffic is so critical, as I still encounter decision makers who just don't get it. Consider Slammer and Code Red, for example, or Slapper and Scalper, or Distributed Denials of Service (DDoS). None of these would have had such a large impact if egress filtering were routinely implemented.

These are just the tip of the iceberg, though; as there's also spyware phoning home, backdoors, Trojans, attacks launched from your systems, employees running activities they shouldn't, and connection hijacking to contend with. And not all "bad" outgoing packets are the result of malice, as a misconfigured router might be lurking in a network. It's important to stop these from spewing wrong packets into the world, too.

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