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Posting

As Seb has already described, the first host/port is for source, the second for destination.

What might further confuse, is which should be port 23.  That depends on which host is the "server" and which host is the "client".  Servers, for many/most services, such as telnet, use a "well known" port on the server.  This is so the "client" knows what port to use when contacting the server.  The client's port might also be "well known" or dynamically assigned.  Which depends on the actual protocol.