Subject: Re: [lisp] LISP Interworking: Proxy Egress Tunnel Routers

From: [email-masked] (Noel Chiappa)
Date: Mon, 21 Sep 2009 21:24:00 -0400 (EDT)

> From: "Joel M. Halpern" <[email-masked]>

    > in order for a site to have the option of avoiding LISP-NAT, someone
    > else has to have sufficient deploy RITRs and PETRs that the sites
    > outbound traffic has PETRs to use, and that inbound legacy traffic has
    > PITRs to use.

Yes, but just like PETRs (in fact, moreso), PITRs are 'bound' to specific LISP
sites. If PITR P is the PITR for EID's E0-En at LISP site L, P has to
advertize those EIDs into the routing, so that packets for E0-En get sent to
P, so it can encapsulate them and send them to L. Presumably P will not do
this unless it has some relationship (involving money) with L. (Either that,
or P belongs to the owner of L.)

Yes, yes, I know there are issues with the location of PITRs and PETRs. But
that's second-order...

    > So, unless there is a deployment model in which PITR and PETR
    > deployments make economic sense, LISP will be dependent upon LISP-NAT.

Do you not believe that demand will drive provision of these services? That's
the way the network grew, let's not forget (i.e. driven by demand).

	Noel

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From: "Joel M. Halpern" <[email-masked]>
Date: Mon, 21 Sep 2009 22:41:31 -0400

Actually, as I understand the PITR proposal, the PITR advertises in BGP 
a short prefix for a large block of EIDs.  If it does not do this, then 
during transition (half of forever), we get an increase in routing table 
size instead of a decrease.
But if the PITR advertises large blocks of EIDs, then it has to serve 
the EIDs within those blocks.  Whether the actual assignee of that block 
has paid for them or not.  (The assignee can not choose a different PITR 
advertiser, because the advertisement is already there.)
Darrel has suggested that folks would do this because it draws traffic 
to them.  But for the most part, that traffic arrives and then leaves. 
Increasing traffic load in both directions does not do an ISP any good. 
  It can cost real dollars.  (There are cases where being able to draw 
traffic for your customers is good.  But the EID prefixes do not 
correspond to ISP customer sets.)
This kind of analysis (what would be advertised, who would advertise it, 
what would the impact be, and why would someone do it) needs to be 
provided at some point.  As Sam has said several times, the degree of 
relevance, and the possible models, depend heavily upon the deployment 
assumptions.

Yours,
Joel