RE: [RRG] Comments on draft-lewis-lisp-interworking

["Darrel Lewis (darlewis)" <darlewis@cisco.com>]

> > You can consider PTRs optional, but NAT is a core 
> requirement for any 
> > sensible interworking between LISP and non LISP-NR sites.
> 
> Can you expand on that a bit please? I have a little trouble 
> parsing "non LISP Non-Routable". And by "NAT" do you mean "LISP-NAT"
> specifically?
> 

Brian,

Sorry about the jargon above.  I was using terms defined in the draft
that aren't very easy to parse.  Also, I think I have a Boolean problem
in the above statement, so let me take it over again from the top.

To be more clear, LISP-NAT and PTR are two ways (they have some nice
synergies, but are independent) for LISP sites whose EIDs are not found
in the DFZ to communicate with non-LISP sites. 

 LISP-NR is a short for LISP-Non Routable, that is a site whose EIDs are
found only in the LISP Mapping database, and _not_ in the Internet DFZ.

 LISP-R is short for  LISP Routable, that is a site whose EIDs are found
both in the LISP Mapping database, and the Internet DFZ. 

LISP-NAT is a form of NAT that allows for LISP-NR addressed hosts to
send packets who's sources get translated to LISP-R addresses.  LISP-NAT
confines the Interworking problem to be site specific, which some sites
may consider a benefit.  It has the classic limitations of NAT,
including the 'global directory' problem:  Which of the two EIDs are in
DNS, the LISP-NR EID, or the LISP-R EID?

PTRs are network elements that advertise (highly) aggregated LISP-NR
space into the DMZ (essentially making it routable).  These devices act
_only_ as ITRs and encapsulate traffic destined to LISP-NR sites.   Note
that return traffic does not back go through the PTR, but is returned
natively (not lisp encapsulated) by the LISP-NR site's xTR to the
originating host.

LISP-NAT can work along side PTRs nicely, I can describe how this works
in more detail if there is interest.  But the trade off in this space is
that PTRs allow for sites not to have to deal with Interworking, at the
cost of connections inbound to the site potentially having stretch.
LISP-NAT allows site independent Interworking, with the (pretty well
understood) limitations of NAT.

Hope this helps explain things more clearly, thanks for your interest.

-D

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