Subject: [lisp] Deployment Document - P-ITR

From: "Joel M. Halpern" <[email-masked]>
Date: Wed, 13 Oct 2010 13:05:06 -0400

First, my thanks to the document authors for getting a document together 
for us.

Speaking purely as an individual participant, I would like to see a lot 
more discussion in the P-ITR section.
In general, I am concerned about the costs and incentives for deploying 
P-ITRs.  Some examples of where I am confused:
One suggested deployment is that EID registars might run P-ITRs.  At 
first glance this seems understandable.  But I do not understand how the 
operational costs line up with the revenue.  As an individual customer 
increases their usage of of P-ITR traffic, how does the EID Registrar 
get revenue to cover their increased costs?
the document also suggests that CDNs might deploy P-ITRs.  There may be 
some advantages to that, but I would really like to see better 
explanation.  After all, the traffic for the CDN has already reached the 
CDN at the point it reaches the P-ITR.  So I am not clear on how it 
helps the CDN customer traffic in a way that they can get paid for.
(I also am not clear as to what set of prefixes the CDN would be 
advertising from its P-ITR.)
The load balancing special case seems to be even more complex, although 
potentially significantly more persuasive.

Thank you,
Joel M. Halpern

---

From: Loránd Jakab <[email-masked]>
Date: Wed, 13 Oct 2010 23:24:54 +0200

Hi Joel,

On 10/13/2010 07:05 PM, Joel M. Halpern wrote:
> First, my thanks to the document authors for getting a document
> together for us.

Thanks for the feedback!

>
> Speaking purely as an individual participant, I would like to see a
> lot more discussion in the P-ITR section.
> In general, I am concerned about the costs and incentives for
> deploying P-ITRs.  

As is the case with other protocols that depend on viable transition
mechanisms in order to be incrementally deployed, I think P-ITR
placement, and, as you say, the associated costs and incentives could be
crucial to the success of LISP. Our document, without being
exhaustive, provided a few examples as a starting point.

>From a theoretical point of view, there are three major deployment types
for P-ITRs:
 - many P-ITRs for each destination prefix, close to the traffic source
(the CDN example below);
 - few P-ITRs in the transit core (the EID registrar example);
 - many P-ITRs for each destination prefix, close to the traffic
destination (xTR + BGP).

Another thing that maybe should be considered while discussing P-ITRs is
the LISP deployment progress (how many networks have migrated to LISP),
because it has a heavy influence on the amount of P-ITR traffic.

See replies to the concerns about the individual cases below:

> Some examples of where I am confused:
> first glance this seems understandable.  But I do not understand how
> the operational costs line up with the revenue.  As an individual
> customer increases their usage of of P-ITR traffic, how does the EID
> Registrar get revenue to cover their increased costs?

I agree that in the initial phase of LISP deployment this is scenario is
unattractive for the EID registrars, except maybe for their smallest
customers. We tried to avoid too much business case discussion in the
draft (I've been told that IETF documents should avoid economics), but
for example a new small customer may get P-ITR service up to a certain
traffic and/or bandwidth limit, above which it would have to look for
alternatives.

Of course, the easiest way is xTR + BGP, but in the case of new Internet
connectivity customers, who also wish to multihome, it defeats the whole
purpose of LISP.

> the document also suggests that CDNs might deploy P-ITRs.  There may
> be some advantages to that, but I would really like to see better
> explanation.  After all, the traffic for the CDN has already reached
> the CDN at the point it reaches the P-ITR.  So I am not clear on how
> it helps the CDN customer traffic in a way that they can get paid for.

The (admittedly unfortunate) use of "CDN" in the draft refers the
company operating it, rather than the concept behind the method of
efficiently delivering large amounts of data. We considered CDNs,
because they are among those with the largest number of geographically
well distributed PoPs.

The CDN does not use the P-ITR for the traffic that it is the
destination of. Rather, the company offers the P-ITR service to clients
that are willing to pay for it. Then, they aggregate the prefixes of all
of their clients, and announce the aggregates from all of their PoPs
(anycast). This leads to a continuous decrease in the DFZ routing table.
When a non-LISP site wishes to connect to any of their clients, it will
use the closest P-ITR (in terms of BGP), thus minimizing path stretch.

> The load balancing special case seems to be even more complex,
> although potentially significantly more persuasive.

All the cases are somewhat uncharted territory, so definitely more
discussion is warranted.

Best regards,
-Lori