William Herrin wrote:
> I can't speak for LISP per se, but the general solution for map-encap
> systems like LISP is that the ITR tags the first packet to the ETR and
> some percentage of subsequent packets to the ETR with an ack request.
> If it doesn't get an ack from the ETR (not the final destination),
> then the ETR or the path to it is depreferenced.
As the ETR is not the final destination, it is subject to blackholing
after ETR, which means:
The function in question can completely and correctly be
implemented only with the knowledge and help of the
application standing at the endpoints of the communication
system.
Granted that it is no worse than multihoming by routing protocols.
But, it merely means that neither BGP nor LISP works "completely
and correctly".
> The path from the ETR to the destination, and by extension the full
> path from the ITR to the destination, is not the ITR's responsibility.
It merely means that LISP is not end to end, because of not ITRs but
ETRs.
In addition, that the ITR, which may be located near the destination
rather than source, can not receive ACKs does not mean the end
system can not receive ACKs, which is ITR related lack of
"completely and correctly" property.
> Some local system is responsible for detecting connectivity between
> the ETR and destination and updating the destination-to-ETR map
> accordingly.
Some local system?
Such a local system must, according to the end to end argument:
The function in question can completely and correctly be
implemented only with the knowledge and help of the
application standing at the endpoints of the communication
system. Therefore, providing that questioned function as a
feature of the communication system itself is not possible.
needs "knowledge and help of the application standing at the
endpoints of the communication system" involving LISP++
specific protocol changes of the end systems.
If you require all the end systems local to ETRs compliant to
some new protocol, do it locally only on the end systems, from
the beginning, without involving intelligent intermediate
entities of *TRs only to make it work not "completely and
correctly"
Masataka Ohta
