Re: Some Comments on ID/Loc Separation Proposals

[Brian E Carpenter <brc@zurich.ibm.com>]

I'd observe that 1122 is fundamentally an IPv4 document. We should
not take it as applying exactly to IPv6, where the notion of an interface is
somewhat different.

   Brian

Juan Rodriguez Hervella wrote:
> 
> On Thursday 13 November 2003 17:12, Erik Nordmark wrote:
> > > An IP address can be used, for example, to allow ULPs to indicate
> > > which physical interface to use for outbound packets by explictly
> > > choosing a source address.  This can be useful for multicast traffic
> > > and specialized ULPs such as routing protocols.
> >
> > I heard this asserted elsewhere yersterday but I haven't seen any IPv*
> > stacks that do such a thing.
> > The outbound interface is selected based on the destination IP address
> > independently of the source address.
> > Thus if the application specifies the source address for if2 and sends
> > a packet to some destination where the routing table for the destination
> > says to use if1, then the packet will go out if1 with the source of if2.
> 
> Hello,
> 
> Quoted from RFC 1122 ("Strong End System" model):
> 
> ---beginning of quotation:
> 
>            There are two key requirement issues related to multihoming:
> 
>             (A)  A host MAY silently discard an incoming datagram whose
>                  destination address does not correspond to the physical
>                  interface through which it is received.
> 
>             (B)  A host MAY restrict itself to sending (non-source-
>                  routed) IP datagrams only through the physical
>                  interface that corresponds to the IP source address of
>                  the datagrams.
> 
>                 o    Strong ES Model
> 
>                       The Strong ES (End System, i.e., host) model
>                       emphasizes the host/gateway (ES/IS) distinction,
>                       and would therefore substitute MUST for MAY in
>                       issues (A) and (B) above.  It tends to model a
>                       multihomed host as a set of logical hosts within
>                       the same physical host.
> 
>                       With respect to (A), proponents of the Strong ES
>                       model note that automatic Internet routing
>                       mechanisms could not route a datagram to a
>                       physical interface that did not correspond to the
>                       destination address.
> 
>                       Under the Strong ES model, the route computation
>                       for an outgoing datagram is the mapping:
> 
>                          route(src IP addr, dest IP addr, TOS)
>                                                         -> gateway
> 
> ----end of quotation
> 
> In short, Erik, under the "strong ES" model assuption,
> your example  would _not_work.
> 
> Ciao !
> 
> --
> ******
> JFRH
> ******