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Introduction
You may notice the following error that is present in the event viewer of your Windows DNS server after configuring your forwarders to use Cisco Anycast resolvers.
After you deploy a Windows-based DNS server, DNS queries to some domains may not be resolved successfully and you may see the Event ID 5501 occuring repeatedly in your event viewer logs.
The DNS server encountered a bad packet from X.X.X.X. Packet processing leads beyond packet length. The event data contains the DNS packet.
Where X.X.X.X might list our external resolvers 208.67.220.220 and 208.67.222.222
This issue occurs because of the Extension Mechanisms for DNS (EDNS0) functionality that is supported in Windows Server DNS.
EDNS0 allows larger User Datagram Protocol (UDP) packet sizes. However, some firewall programs may not allow UDP packets that are larger than 512 bytes. Therefore, these DNS packets may be blocked by the firewall.
EDNS0 allows larger User Datagram Protocol (UDP) packet sizes. However, some firewall programs may not allow UDP packets that are larger than 512 bytes. Therefore, these DNS packets may be blocked by the firewall.
Environments affected
Windows Server 2008 R2
Windows Server 2003
Resolution
A full solution to this problem can be found in the Microsoft support article linked below:
Some DNS name queries are unsuccessful after you deploy a Windows-based DNS server