4.3 TCP support

MyDNS will process all TCP requests it receives if the configuration option `allow-tcp' is true. This is not usually necessary or recommended. TCP support will make the server run a little slower, and a denial-of-service attack is easier if TCP is allowed.

Some very large sites may require TCP support, however. If a response set would exceed the UDP message size limit (512 bytes), MyDNS will set the TC (truncated) flag on its answer. Some clients will then fall back to TCP, which can handle such large answers. If TCP support is enabled, those clients can get their responses. Also, TCP support is required to perform DNS-based zone transfers.