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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] iSCSI: Concerns raised about ACA and denial of service conditionsThe SCSI Commands, Architecture, and Protocols working group reviewed a proposal by Ed Gardner based on input from Julian Satran, the intent of which is to invoke ACA when a BUSY, TASK SET FULL, or RESERVATION CONFLICT status occurs. The CAP working group had several questions regarding the need for this proposal. Ed and I explained as best we could the iSCSI need for this capability to support high latency links. Generally, our explanations were deemed inadequate and several calls were heard along the lines of "if this is so important why isn't anybody here to defend it?" However, that was not the worst of the troubles visited on the proposal. Several people noted problems with using ACA to preserve synchronization following a rejected command, since ACA locks out all initiators, not just the one initiator whose command was rejected. For example, suppose one initiator holds a reservation. A second initiator sends a command and gets back RESERVATION CONFLICT, causing an ACA. The first initiator cannot access the device until the second initiator clears the ACA. If the second initiator simply does nothing (whether maliciously or due to crashing), the first initiator is permanently locked out from accessing the device it has reserved. Ed plans to be in London and will be happy to discuss this there. I will miss London due to the T11 meeting. The T10 CAP working group is seeking clarification from the iSCSI team regarding their desires in this matter. Is a feature that opens opportunities for denial of service attacks really the desired result? If not, it is the opinion of the CAP working group, that ACA is not the desired mechanism and further consideration of the real requirements is needed. All responses to this message will be collected in a T10 document for delivery to the CAP working group. It is advisable that someone who can defend the iSCSI requirements attend the next CAP working group meeting to be held Wednesday, September 12, 2001 from 9 a.m. to 7 p.m., continuing if necessary on Thursday, September 13, 2001 from 8:00 a.m. to 9:45 a.m. (or until all agenda items are completed). The meeting will be at the Hilton Waterfront Hotel (714-960-7873) in Huntington Beach, CA, hosted by QLogic. More information on the meeting can be obtained from the T10 web site www.t10.org. Thanks. Ralph...
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