Broadcasts - TCP or UDP - TCP-IP

This is a discussion on Broadcasts - TCP or UDP - TCP-IP ; Hi, I have seen various posts that say TCP cannot be used for Broadcasts. Does that still hold true? If so what is the directed broadcast feature. Thanks...

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  1. Broadcasts - TCP or UDP

    Hi, I have seen various posts that say TCP cannot be used for
    Broadcasts. Does that still hold true? If so what is the directed
    broadcast feature. Thanks


  2. Re: Broadcasts - TCP or UDP

    In article <1155917409.318546.176310@75g2000cwc.googlegroups.c om>,
    newbie123 wrote:
    >Hi, I have seen various posts that say TCP cannot be used for
    >Broadcasts. Does that still hold true? If so what is the directed
    >broadcast feature. Thanks


    A) You aren't going to be able to complete a TCP handshake using
    broadcasts.

    B) Most implementations will ignore completely ignore TCP packets
    directed towards a listening socket, until they see a TCP SYN
    packet.

    Thus even if you did send out a TCP packet to the directed broadcast
    address, then it would have to be a SYN packet to have any chance
    of reception... and then what would you do with the replies if you
    got them?


  3. Re: Broadcasts - TCP or UDP

    "newbie123" writes:
    > Hi, I have seen various posts that say TCP cannot be used for
    > Broadcasts. Does that still hold true?


    Yes.

    > If so what is the directed
    > broadcast feature. Thanks


    Directed broadcast refers to an IP datagram that has a destination
    address that is a (sub)network broadcast on some non-local network.
    The sender of that packet expects that routers will forward this
    packet, and that the last-hop router will turn it into a subnetwork
    broadcast.

    It's unwise for that last router to do that, as documented in RFC
    2644, among other places.

    Are you perhaps confusing the transport layer protocol called "TCP"
    with the entire TCP/IP protocol suite?

    --
    James Carlson, KISS Network
    Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

  4. Re: Broadcasts - TCP or UDP

    "newbie123" wrote:

    > Hi, I have seen various posts that say TCP cannot be used for
    > Broadcasts. Does that still hold true? If so what is the directed
    > broadcast feature. Thanks


    TCP is an end-to-end acknowledged protocol. So it only applies to
    sessions between two hosts. Multicast or broadcast (broadcast only spans
    the hosts of one IP subnet, even if initiated remotely from that subnet)
    by definition do not create point to point sessions between just two
    hosts. In both cases, the sender is simultaneously transmitting
    datagrams to many other hosts. So clearly, the handshaking TCP does to
    initiate and end sessions, and the ACK packets flowing back from the
    destination to the source, would not apply to multicast or broadcast.

    Directed broadcast is simply a way for a host in Subnet A to broadcast
    datagrams to all hosts in Subnet B. It's a special case of broadcast.
    Otherwise, broadcast in IP is strictly limited to hosts within just one
    subnet.

    So directed broadcast does not change anything in this regard. TCP is
    not compatible with a one-to-many or many-to-many scenario.

    Bert


  5. Re: Broadcasts - TCP or UDP

    "James Carlson" wrote:

    > Are you perhaps confusing the transport layer protocol called "TCP"
    > with the entire TCP/IP protocol suite?


    I wish that practice would stop, already. I prefer to call it the IP
    suite, myself. This causes no end of confusion when clueless
    requirements writers get stuck on insisting it must be "TCP."

    Bert


  6. Re: Broadcasts - TCP or UDP

    "Albert Manfredi" writes:
    > "James Carlson" wrote:
    >
    > > Are you perhaps confusing the transport layer protocol called "TCP"
    > > with the entire TCP/IP protocol suite?

    >
    > I wish that practice would stop, already. I prefer to call it the IP
    > suite, myself. This causes no end of confusion when clueless
    > requirements writers get stuck on insisting it must be "TCP."


    Do let us know when you've beaten that windmill into submission, ok?

    ;-}

    --
    James Carlson, KISS Network
    Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

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