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1221

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The tag 1221 refers to a specific UDP packet size setting recommended by Microsoft to mitigate DNS cache poisoning attacks. In advisory ADV200013, Microsoft instructs administrators to set the MaximumUdpPacketSize registry value to 1221 bytes on Windows DNS servers. This configuration forces DNS responses larger than 1221 bytes to use TCP instead of UDP, reducing the risk of spoofing and cache poisoning. The mitigation applies to Windows Server 2022, 2025, and other supported builds. Discussions on WindowsForum.com cover implementing this fix, verifying the setting, and understanding its impact on DNS performance and security.
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    Windows DNS Cache Poisoning Mitigation: Set MaximumUdpPacketSize to 1221 (ADV200013)

    Microsoft has updated guidance in its Security Update Guide advisory ADV200013 — the advisory that covers DNS resolver spoofing and cache‑poisoning attacks — and is explicitly telling administrators that in addition to older server builds the mitigation applies to newer releases such as Windows...
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    • 1221 adv200013 dns dns cache dns forwarders dns over tcp dns registry dns security edns0 firewall dns tcp maximumudppacketsize powershell registry hardening security tips server core tcp dns latency windows server windows server 2022 windows server 2025
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    • Forum: Security Alerts
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