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参考资料
RFC 1035 - Domain names - implementation and specification:
4.2.1. UDP usage
Messages sent using UDP user server port 53 (decimal).
Messages carried by UDP are restricted to 512 bytes (not counting the IP
or UDP headers). Longer messages are truncated and the TC bit is set in
the header.
UDP is not acceptable for zone transfers, but is the recommended method
for standard queries in the Internet. Queries sent using UDP may be
lost, and hence a retransmission strategy is required. Queries or their
responses may be reordered by the network, or by processing in name
servers, so resolvers should not depend on them being returned in order.
The optimal UDP retransmission policy will vary with performance of the
Internet and the needs of the client,........................... |
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楼主: dreamhunter
发表于 2010-07-14 14:46
发表于 2010-07-16 07:35
