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    RE: iSCSI: IP fragmentation



    Mandating special behavior between the IP stack and the TCP stack is outside
    the scope of the IPS charter.  However, a TCP stack that implements PMTU
    discovery already sets the DF bit in IP packets.  It seems reasonable to
    state recommendations regarding the RFCs implemented by the TCP stack that
    iSCSI is running on top of, like "the TCP stack SHOULD support RFC 1191,
    <etc>"  Implementors should also be aware of RFC 1435 and RFC 2923.
    
    Marjorie Krueger
    Networked Storage Architecture
    Networked Storage Solutions Org.
    Hewlett-Packard
    tel: +1 916 785 2656
    fax: +1 916 785 0391
    email: marjorie_krueger@hp.com 
    
    > -----Original Message-----
    > From: Joshua Tseng [mailto:jtseng@NishanSystems.com]
    > Sent: Thursday, June 07, 2001 6:10 PM
    > To: ips@ece.cmu.edu
    > Subject: iSCSI: IP fragmentation
    > 
    > 
    > 		Folks,
    > 
    > 		IP fragmentation is an issue which will affect the
    > performance, logic and
    > 		HBA/NIC memory requirements of iSCSI 
    > implementations. Note
    > that
    > 		fragmentation by intermediary switches and 
    > routers is not
    > permitted
    > 		in IPv6 (hence, the DO NOT FRAGMENT bit does 
    > not exist in
    > IPv6).
    > 		With this in mind, and in the interest of 
    > optimizing iSCSI
    > performance,
    > 		I was wondering if it would make sense to 
    > require that the
    > 		DO NOT FRAGMENT bit to be set on IPv4 packets 
    > carrying iSCSI
    > and
    > 		that iSCSI implementations not perform IP 
    > fragmentation for
    > IPv6.
    > 		This will allow for performance optimization if
    > implementations do not
    > 		have to check for fragmentation and handle reassembly.
    > 
    > 		Any thoughts?
    > 
    > 		Josh
    > 
    


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Last updated: Tue Sep 04 01:04:32 2001
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