port
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_Service._Proto.Name TTL Class SRV Priority Weight Port Target
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... Hosts that are referenced by backup address records must use the
port number specified in Assigned Numbers for the service.
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... The Port number ...
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Currently, the translation from service name to port number happens
at the client, often using a file such as /etc/services ...
... Port numbers SHOULD NOT be used in place of the symbolic service
or protocol names (for the same reason why variant names cannot
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... The ability to specify ports on a fine-grained basis obviously
changes how a router can filter packets ...