Internet Direct (Indy) Version 9.0.2 Beta
TDNSHeader.TC
Indicates if a DNS response message packet has been truncated due to excessive length.

property TC: Word;
Description
TC is a Word property that indicates if a DNS response message packet has been truncated when the length of the message packet exceeds the maximum permitted on the transmission channel. TC will contain the value 1 when the mesaage packet has been truncated, or the value 0 when the packet contains the entire response issued by the name server.

Messages handled by the UDP-based DNS Resolver are restricted to 512 bytes (not counting the UDP headers). Longer messages are truncated and TC is set to 1 in the header. For this reason, the UDP-based TIdDNSResolver does not implement DNS zone transfers, but is the recommended method for standard queries in the Internet.

TC is represented in a DNS header as a bit field. Changing the value of TC insures that the appropriate bit field is updated in the DNS header for the message packet.