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    Fw: Re: iSCSI Marker questions




    ----- Forwarded by Julian Satran/Haifa/IBM on 12-12-01 02:39 -----
    Julian Satran

    11-12-01 14:44


            To:        IPS List
            cc:        
            Subject:        Re: iSCSI Marker questionsLink



    Dean,



    owner-ips@ece.cmu.edu wrote on 11-12-2001 03:09:11:

    > The iSCSI Draft 9 Appendix C makes the following statements about
    > Markers and the Initial Marker-less Interval:
    >
    >      "The offset to the next iSCSI PDU header is counted in terms
    >       of the TCP stream data. Anything counted in the TCP
    >       sequence-number is counted for the offset. Specifically this
    >       includes any bytes "inserted" in the TCP stream by an UFL and
    >       it excludes any other markers inserted between the one we are
    >       examining and the next PDU header."...
    >
    >      "To enable the connection setup including the login phase
    >       negotiation, marking (if any) is started only at the first
    >       marker interval after the end of the login phase."
    >
    > I understand that markers are not inserted until after login phase.
    > Am I correct to assume that the placement of the first marker
    > determined by the TCP sequence numbers on the final Login Request/
    > Response PDUs, or is initial marker position determined by the
    > TCP sequence numbers at connection establishment?
    >
    > Assume the following interaction:
    >
    > I->  SYN     (TCP sequenceNum=1000)  -- irrelevant to this discussion?
    >
    > T->  SYN-ACK (TCP sequenceNum=2000)  -- irrelevant to this discussion?
    >
    > I->  Login Request PDU, T=0,CSG=1,NSG=0:
    >      InitiatorName=xxx
    >      TargetName=yyy
    >      SessionType=normal
    >      ...
    >      FMarker=send-receive
    >      RFMarkInt=512,1024
    >
    > T->  Login Response PDU, T=0,CSG=1,NSG=0:
    >      ...
    >      FMarker=send-receive
    >      SFMarkInt=1024
    >      RFMarkInt=1024
    >
    > I->  Login Request PDU, T=1,CSG=1,NSG=3:
    >      SFMarkInt=1024
    >      (64-byte PDU... TCP sequenceNum=1301-1364)
    >
    > T->  Login Response PDU, T=1,CSG=1,NSG=3:
    >      (48-byte PDU... TCP sequenceNum=2201-2248)
    >
    > The above interaction designates a 1024 x 4 = 4096-byte marker
    > interval in both directions. The first PDU byte sent by the
    > intitiator in full-feature mode will have sequenceNum=1365, and
    > the first byte sent by the target will have sequenceNum=2249.
    >
    > Assuming the markerless interval starts at the end of login
    > phase, the first two markers in each direction will have the
    > following TCP sequence numbers:
    >
    >                TCP SeqNum of    TCP SeqNum of
    >                First Marker     Second Marker
    >                ------------     -------------
    > Initiator:     5461-5468        9565-9572
    > Target:        6345-6352        10449-10456
    >

    No - the correct numbers are dependent only on the marker interval (not the length of the login phase) and are:

    Initiator        5096-5103        9200-9201
    Target           6096-6103        10200-10201
     
     
    > Is this the correct interpretation of marker usage in iSCSI
    > Draft 9, or does marker placement depend on the connection's
    > initial sequence numbers?
    >
    > Also, is "RFMarkInt=..." always considered an offer, and "SFMarkInt="
    > considered a reply to that offer? If an offer is sent with "FMarker=..."
    > and "RFMarkInt=...", MUST the reply contain either "FMarker=no" or
    > BOTH "FMarker=yes" and "SFMarkInt=..."?
    >


    Fmarker is not boolean - legal values are no, send, receive, send-receive
    The sender and receiver must set the interval it wants/is ready to use
    otherwise the responder can't answer.
    I assume a normal dialogue may go like:

    I->FMarker=send-receive,RFMarkInt=1,4,SFMarkInt=1,512
    T->FMarker=send-receive,RFMarkInt=8, SFMarkInt=2

    Please observe that target answers with RFMarkInt to the initiators SFMarkInt and viceversa.

    I will attempt an example in draft 10 (last?).


     
    > Thanks,
    > Dean Scoville
    > QLogic Corp.



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