Putting aside the TBD (which of course needs to be fixed), I have
trouble figuring out what you want us to say about the main issue in
your review. On the one hand, this is the very issue that we have been
asked to comment on, and on the other hand you say that we don't know.
What do you think it is reasoanble to say?
Yours,
Joel
On 3/29/15 9:03 PM, Ross Callon wrote:
Generally I think that this document needs more work before it will be
ready to submit for publication. Some comments on draft-ietf-lisp-impact-01:
First of all, I assume that the TBD at the end of section 3 will be
fixed. This reads:
TBD: add a paragraph to explain the operational difference while
dealing with a pull model instead of a push.
Also in section 3, the third paragraph begins:
In addition, Iannone and Bonaventure [IB07] show that the number of
mapping entries that must be handled by an ITR of a campus network
with 10,000 users is limited to few tens of thousands, and does not
represent more than 3 to 4 Megabytes of memory.
Reference [IB07] is of course:
Iannone, L. and O. Bonaventure, "On the cost of caching
locator/id mappings", In
Proc. ACM CoNEXT 2007, December 2007.
This paper states:
In our analysis, we assume that the granularity of the
EID-to-RLOC mapping is the prefix blocks assigned by
RIRs. We call it /BGP granularity. In particular, we
used the list of prefixes made available by the iPlane
Project [15], containing around 240,000 entries. Using
/BGP granularity means that each EID is first mapped
on a /BGP prefix. The cache will thus contain /BGP
to RLOC mappings.2 This is a natural choice, since
routing locators are supposed to be border routers.
The authors should be aware that there is some aggregation /
summarization being done in the operation of BGP routing, and that the
granularity of routes which appear in the default-free BGP routing
tables is fundamentally different from the granularity of enterprise
network / ISP boundaries across which traffic is exchanged.
The same paragraph cites Kim et al. [KIF11], which is Kim, J., Iannone,
L., and A. Feldmann, "Deep dive into the lisp cache and what isps should
know about it", In Proc. IFIP Networking 2011, May 2011. From this
document:
In addition, we use a local BGP prefixes
database, fed with the list of BGP prefixes published by the iPlane
Project [17].
The database is used to group EID-to-RLOCs mappings with the
granularity of
existing BGP prefixes, because, as for today, there is no
sufficient information
to predict what will be the granularity of mappings in a
LISP-enabled Internet.
I agree that “there is not sufficient information to predict what will
be the granularity of mappings in a LISP-enabled Internet”. However, not
knowing what the mapping granularity will be does not justify using an
extremely optimistic guess, and then acting as if the results are
meaningful. These assumptions are clearly off by some number of orders
of magnitude, but how many orders of magnitude is unknown. We will note
that the current internet default-free routing table includes a few
hundred thousand entries (roughly twice the 240,000 entries that existed
when this study was done).
For example, we might assume that the intended global deployment model
involves xTRs at the boundary between enterprise networks and service
providers, and might note that there are several million companies in
the USA alone (most of these are relatively small companies, of course).
Thus there may be very roughly on the order of a hundred million or so
companies worldwide. If each one had a separate entry in the mapping
table, then the number of entries will be nearly 1,000 times larger than
BGP-prefix granularity.
Section 4 mentions as one possible use of LISP: “enable mobility of
subscriber end points”. If individual end points are advertised into
LISP, then the granularity of the mapping table may be on the order of
individual systems. In this case the number of mapping table entries
that could exist globally might be on the same order of magnitude as the
number of people in the world, or very roughly 7 Billion entries. This
would suggest that the mapping table might be roughly 30,000 times finer
grained than was assumed in the referenced studies.
I don’t see how we can accurately predict the control plane load of LISP
without some sense for what the granularity of the mapping table will
be. It should however be possible to bound the control plane load. The
referenced studies give a lower bound on possible control plane load (it
won’t be any less), but give neither an accurate measurement nor an
upper bound on the potential control plane load. I don’t think that the
document can claim to explain the impact of LISP without there being an
attempt to measure an upper bound on the control plane load.
Finally, perhaps I missed it but I didn’t see any discussion of the
volume of overhead related to OAM traffic used for liveness detection
(the need for ITR’s to determine the reachability of ETR’s).
Thanks, Ross
*From:*lisp [mailto:[email protected]] *On Behalf Of *Luigi Iannone
*Sent:* Monday, March 09, 2015 10:22 AM
*To:* LISP mailing list list
*Cc:* [email protected]
*Subject:* [lisp] WG Last Call draft-ietf-lisp-impact-01
Hi All,
the authors of the LISP Impact document
[https://tools.ietf.org/html/draft-ietf-lisp-impact-01] requested the
Work Group Last Call.
This email starts a WG Last Call, to end March 30th, 2015.
Because usually the pre-meeting period is already overloaded, the LC
duration is set to three weeks.
Please review this updated WG document and let the WG know if you agree
that it is ready for handing to the AD.
If you have objections, please state your reasons why, and explain what
it would take to address your concerns.
Any raised issue will be discussed during the WG meeting in Dallas.
Thanks
Luigi & Joel
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