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We propose a framework based on proactive server roaming to mitigate the effects of denial-of-service (DoS) attacks. The active server proactively changes its location within a pool of servers to defend against unpredictable and undetectable attacks. Only legitimate clients can follow the active server as it roams. We present algorithms that are secure, distributed, randomized, and adaptive for triggering the roaming and determining the next server to roam to. We propose some modifications to the state recovery process of existing TCP connection-migration schemes to suit roaming. Preliminary experiments in a FreeBSD network show that the overhead of server roaming is small, in terms of response time, in the absence of attacks. Further, during an attack, roaming significantly improves the response time.