SPI question

"Amal Maalouf" <amalmaal@nortel.ca> Wed, 27 May 1998 12:23 UTC

Received: (from majordom@localhost) by portal.ex.tis.com (8.8.2/8.8.2) id IAA20424 for ipsec-outgoing; Wed, 27 May 1998 08:23:08 -0400 (EDT)
Message-Id: <199805271234.IAA15259@relay.hq.tis.com>
Date: Wed, 27 May 1998 08:36:00 -0400
To: ipsec@tis.com
From: Amal Maalouf <amalmaal@nortel.ca>
Subject: SPI question
Sender: owner-ipsec@ex.tis.com
Precedence: bulk

Hello,

Please can anyone clarify the following..

When two end systems are negotiating an SA using Quick mode,
the initiator sends an ISAKMP message with the SA payload,
proposal payload(s) and transform payload(s).  What does
the initiator fill in the SPI field of the proposal payload?
Is this SPI used at all to identify the SAs created on both
sides?  
I understood from reading the AH/ESP drafts that it is the responder
that specifies the SPI that the initiator is to use in the
AH header and/or ESP header sent to the responder.  I figuered
that this SPI is sent from the responder to the initiator
when the responder chooses one of the proposals that the initiator
is suggesting, i.e. when the responder responds in the SA Quick
mode negotiation.  If this is the case, then what is the SPI field
set by the initiator in this negotiation used for?

Thanks,
Amal.