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    RE: A couple of iFCP questions



    David,
    
    > 
    > A couple of questions about iFCP:
    > 
    > (1) iFCP has been described as NAT-like in translating
    > 24-bit FC identifiers (S_ID and D_ID) to an IP address of
    > another iFCP gateway and a 24 bit identifier with respect
    > to that gateway.  The iFCP document describes how
    > translations are accumulated by an iFCP gateway.  How
    > are they discarded?  To be specific, when and under
    > what circumstances is it safe for a gateway to discard
    > a (no longer used) translation, and what are the consequences
    > of an erroneous discard?
    
    It is safe to discard a translation when there are no active N_PORT
    sessions for a remote N_PORT.  In that case, the iFCP gateway SHOULD
    invalidate and remove the mapping to that remote N_PORT.  Of course,
    even if it doesn't, a device establishing a new N_PORT session has the
    responsibility of validating any pre-existing mapping by checking WWPN's
    of the remote device.
    
    An erroneous discard of an FC_ID mapping would be the result of a bug,
    and we would consider it to be fatal iFCP gateway error.  While the
    handling of such an error is implementation-specific, we would expect
    some sort of fail-safe behavior.
    
    In Fibre Channel, the fabric is responsible for assigning
    the FC identifiers (used in S_ID and D_ID).  The iFCP gateway
    will emulate this behavior in response to the FLOGI by assigning
    its own locally-significant (to that particular iFCP gateway)
    FC identifiers.  The behavior of the iFCP gateway should be no
    different from any other FC fabric with regard to address assignment
    and reassignment.
    > 
    > (2) If an FC fabric were to be connected to an iFCP gateway,
    > the fabric may change how the 24 bit identifiers
    > are mapped to ports (as identified by Port WWN) in some
    > circumstances (recabling can cause this).  When
    > such a change occurs, does this invalidate translations
    > in other iFCP gateways?  If yes, how do those gateways find
    > out/get updated translations in a fashion that ensures traffic
    > will not be delivered to the wrong FC port?  If not, what
    > does the first iFCP gateway do to preserve the old versions
    > of the changed translations?
    
    Anything resulting in a change to the value
    of the 24-bit FC identifiers would be a major event, in
    both FC and iFCP.  If it should occur, the iFCP gateway shall
    immediately terminate the N_PORT sessions and supporting TCP
    connections affected by the changed FC identifier.  This
    includes events such as LIPs and cable disconnect.  Following
    such an event, the iFCP gateways should automatically update
    their FC_ID mappings in the normal process of re-establishing
    N_PORT sessions.
    
    iSNS facilitates the interoperation among iFCP gateways.  iSNS
    is how other iFCP gateways learn of the FC identifier mappings
    to IP address and WWPN.  If these mappings are changed, the iFCP
    gateway shall register the change in the iSNS (and as mentioned
    before, the old N_PORT sessions will be terminated).  The iSNS server
    in turn, will issue state change notifications to all affected
    iFCP gateways, informing them of the new 24-bit FC identifer
    mappings.  
    
    Josh
    > 
    > Thanks,
    > --David
    > 
    > ---------------------------------------------------
    > David L. Black, Senior Technologist
    > EMC Corporation, 42 South St., Hopkinton, MA  01748
    > +1 (508) 435-1000 x75140     FAX: +1 (508) 497-8500
    > black_david@emc.com       Mobile: +1 (978) 394-7754
    > ---------------------------------------------------
    > > 
    


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Last updated: Tue Sep 04 01:06:01 2001
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