On Wed, 12 Apr 2000, Dick St.Peters wrote:
Quoted from RFC791, the IP specification, in the section on loose
source routing, page 19 [emphasis added]:
If the address in destination address field has been reached and
the pointer is not greater than the length, the next address in
the source route replaces the address in the destination address
field, and the recorded route address REPLACES THE SOURCE
ADDRESS just used, and pointer is increased by four.
The recorded route address is the internet module's own internet
address as known in the environment into which this datagram is
being forwarded.
An end-to-end-inviolate source address is not a required part of the
IP spec.
The authors of the standard had the vision to foresee that rewriting
the source address might be desireable under some circumstances. They
were off target about when this might be used, but they designed a
protocol flexible enough to encompass things they could not foresee.
I think you have misunderstood what the RFC intended to say. The "source
address" being replaced is the entry in the LSRR option that is being
written into the destination field, not the source address in the IP
header, which is supposed to remain constant throughout its journey.
Anyway, a source route option was intended to be something that the
originating host puts into the datagram, and so the destination address
rewriting that does happen is being done by explicit request of the
originating host. That's quite different from what an interception
proxy does, isn't it?
C. M. Heard
heard(_at_)vvnet(_dot_)com