[1] draft-cai-ssdp-v1-03 - Simple Service Discovery Protocol/1.0 ( (3/20/2011, 3:41:36 PM 版)) <http://tools.ietf.org/html/draft-cai-ssdp-v1-03#section-4.2.1.1>
[2] RFC 7505 - A "Null MX" No Service Resource Record for Domains That Accept No Mail (7/1/2015, 1:19:40 AM 版) <https://tools.ietf.org/html/rfc7505>
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