When a computer that is running Microsoft Windows Server 2003 makes an external DNS query, you may receive one of the following error messages:
Server unable to interpret format
This problem may occur on some Cisco PIX Firewall models with software that is earlier than PIX Firewall version 6.3(2). The Cisco PIX Firewall drops DNS packets sent to User Datagram Protocol (UDP) port 53 that are larger than the configured maximum length. By default, the maximum length for UDP packets is 512 bytes.
This problem may occur if the external DNS server does not support Extension Mechanisms for DNS (EDNS0) or if a firewall exists between your server and the external DNS server. DNS servers that do not support EDNS0 cannot process EDNS0 data, and this behavior causes the query to fail. Some firewalls may drop the EDNS0 packets that are sent by servers that support EDNS0, or may drop UDP packets that are larger than 512 bytes that are sent by servers that support EDNS0.
To resolve this problem, visit the following Cisco Systems Web site for information and update instructions:
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