passive opens

This is a discussion on passive opens within the Networking/Device Communication forums, part of the General Programming Boards category; under "TCP Statistics for IPv4" there is a listing for passive opens. active opens..... passive opens..... Can a passive open ...

  1. #1
    Registered User kryptkat's Avatar
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    passive opens

    under "TCP Statistics for IPv4" there is a listing for passive opens.

    active opens.....
    passive opens.....

    Can a passive open be done through a firewall? yes i think. More info needed on passive opens. Or opening a port discreatly by listening.

    rfc 793

    A passive OPEN request means that the process wants to accept incoming
    connection requests rather than attempting to initiate a connection.
    Often the process requesting a passive OPEN will accept a connection
    request from any caller. In this case a foreign socket of all zeros
    is used to denote an unspecified socket. Unspecified foreign sockets
    are allowed only on passive OPENs.
    Any port listening and wanting to make a connection must do so with the permission of the user and firewall. If not what case would a socket connect with out permission of firewall or user?
    why would a prog want to make a passive open? updates and what else? <besides trojjiez> smtp?

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    Can a passive open be done through a firewall?
    It depends on how the firewall is configured. A passive open is just a call to bind(). Some firewalls might let this happen without notifying the user, but most firewalls will require the user's permission before a bind() can be successfully completed.

    If not what case would a socket connect with out permission of firewall or user?
    Once again, this depends on how the firewall is configured. Many firewalls by default allow outgoing (active opens) connections, but block incomming connections. This is all configurable in any modern firewall though.

    why would a prog want to make a passive open?
    Any type of server application needs to do a passive open to listen for connections. Web servers, mail servers, game servers, etc.

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