TCP
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...
Proto
TCP and UDP are at present the most useful values
for this field, though any name defined by Assigned Numbers or
...
... internet site adds a SRV RR for Telnet/TCP is futile (even if
desirable). Therefore SRV will have to coexist with A record ...
... - A future standard could specify that a SRV RR whose Protocol was
TCP and whose Service was SMTP would override RFC 974(-> 2821prop) ...