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Problem Statement: Overlays for Network Virtualization
RFC 7364

Yes

(Stewart Bryant)

No Objection

(Gonzalo Camarillo)
(Martin Stiemerling)
(Richard Barnes)

Note: This ballot was opened for revision 03 and is now closed.

Jari Arkko Former IESG member
Yes
Yes (2013-06-27 for -03)
Thank you for writing this document. It is well written and easy to read, and documents the space well.

I had one question when reading Section 4. I was wondering why MTU was not mentioned, MTU issues being one of the impacts of overlay designs.
Stewart Bryant Former IESG member
Yes
Yes (for -03)

                            
Adrian Farrel Former IESG member
No Objection
No Objection (2013-06-26 for -03)
Thanks for this document which I believe is a major step towards scoping
and documenting the real problems in this space.  I have a number of
fairly editorial concerns that I hope you can work through with your AD
and document shepherd.

---

In reading this document, I found it difficult to distinguish the 
requirements that arrise from the provision of multiple virtual networks
on a common infrastrucutre (traffic isolation, address space isolation,
virtual network creation and configuration) from those that are specific
to the NVO3 scope (massive scaling, multi-tenancy on individual physical
servers, no constraints on physical location of hosted services).

---

[I-D.ietf-nvo3-framework] is used as a normative reference because it 
defines terminology used in this document.

---

I would move the definiton of "in-band virtual network" from section 2
to section 5.3 (the only place the term is used) to avoid complicating 
the definitions with concepts that appear to only be applied to L2
networks.

---

Why is the example of an Overlay Virtual Network in section picked from
the layer 2 space when this work is supposed to consider only layer 3
overlays?

OTOH, since this term is not used anywhere in the document, I suggest
deleting it.

---

I believe section 3.1 could be rewritten without the need to say "cloud"
or "elastic services".  This would be helpful because those marketting
phrases do not add to the meaning.

I think the final sentence of the paragraph captures the issues, but 
could be pulled out into a little more explanation of what happens and
what problems it causes.

---

Section 5.3 uses the terms C-VLAN, S-VLAN, and B-VLAN, but only C-VLAN
has been defined.

--

Section 10 seems to me to be missing the impact that one virtual network
might be able to have on another (for example by stressing network
resources to cause undesirable VM mobility, or by consuming shared 
resources to make b/w or CPU unavailable).

This is a type of self-consuming DoS.
Barry Leiba Former IESG member
No Objection
No Objection (2013-06-21 for -03)
Editorial:
In Section 5.6, I think the second and third sentences need to be merged with a comma.
Benoît Claise Former IESG member
No Objection
No Objection (2013-06-27 for -03)
Not much OPS feedback in this draft. I'm dying to see the "Operational Requirements submitted for IESG review" chartered item.

Editorial:
"Tenant Systems" should not be capitalized. Alternatively, you can define the term.
Please expand ARMD
Explain/Expand: C-VID, B-VID, I-VID 

And here is Melinda's feedback from OPS-DIR:
I was asked to perform an OPS-DIR review of
draft-ietf-nvo3-overlay-problem-statement.

The document specifically targets multitenancy in large data
center networks, describing problems arising from that
scenario and how they may be addressed by overlay networks.
That this document made it through working group last call
at all should be seen as a major political accomplishment,
given the level of rancor in the working group, and much
respect is due to the chairs and the document authors for
getting this done.

The underlying assumption is that these virtual networks
will provide traffic isolation.

Minor issues:

Section 3.1: "Cloud computing" - the document would benefit
from eliminating that terminology and just describing the
scenario ("Some service providers offer elastic services
... ").  "Cloud" is imprecise and evocative of marketing
jargon.  We can talk about the need for dynamic provisioning
more carefully, I think.

Section 3.2, second sentence: "A VM can be migrated from
one server to another, [ ... ]."  I'm afraid it's servers
all the way down - may be clearer to say that VMs may be
migrated between hypervisors.

An operational consideration for this section (3.2) is that
there may be state associated with specific data flows to a
VM that is not on the VM - that's resident on some sort of
middlebox (firewall, application proxy, accelerator, cache,
etc.).  I tend to think that network state will, in
practice, be topologically close to the VM, but care must be
taken.

Doesn't really matter but it appears that the section header
for section 3.6 is marked up incorrectly (font and bolding).

3.7 is probably one of the clearest descriptions I've seen
of this issue - well done.

10: I'm not sure the security considerations are quite right, or
at least not the discussion of data plane security issues.
What are the characteristics of an overlay network that
differ from a physical network or VPN, and how do they
impact design decisions for the overlay?

Also, may be worth saying something about data leakage from
interception of control plane traffic (what inferences can
be made from changes in topology, etc.?).
Gonzalo Camarillo Former IESG member
No Objection
No Objection (for -03)

                            
Joel Jaeggli Former IESG member
No Objection
No Objection (2013-06-27 for -03)
The document is weirdly though non-specifically ipv4-centric. I don't think there are any particular fixes to be applied. I would observe however that address reuse while common in parallel rfc1918 addressing planes would not I imagine be very common in ipv6 in the umbering plans of ipv6 enabled DCs. that the longest possible route is not a /32, and that a signficant scaling consideration with L3 --> L2 mappings is the duplication between the arp cache and the NDP cache.
Martin Stiemerling Former IESG member
No Objection
No Objection (for -03)

                            
Richard Barnes Former IESG member
No Objection
No Objection (for -03)

                            
Sean Turner Former IESG member
No Objection
No Objection (2013-06-27 for -03)
I support Stephen's discussion position.
Spencer Dawkins Former IESG member
No Objection
No Objection (2013-06-21 for -03)
I did have one comment. Please consider it along with any other comments you receive.

This draft uses the word "cloud", which has been an extremely imprecise term in the IETF. 

The second occurrence in Section 3.1 provides some guidance on which of the (many) aspects of clouds you're talking about:

   Cloud computing involves on-demand provisioning of resources for
   multi-tenant environments. 

Could this explanation be moved to Section 1, with the first occurrence of "cloud"?
Stephen Farrell Former IESG member
(was Discuss) No Objection
No Objection (2013-06-27 for -03)
The nodes of a virtual network, once running, can look
after securing their own traffic. That might lead one to
say that nvo3 traffic isolation doesn't need to consider
confidentiality. However, if the nodes in a virtual network
are VMs and if VMs can be moved, then any secrets required
for the virtual network to secure its traffic will be
exposed to the underlay during the move. 

I'm not clear if this wg will try address that issue or
not. Section 10 does say that some environments might be
concerned about confidentiality but is vague about whether
or not the wg will work on the topic.

Such a confidentiality service isn't a panacea of course,
the underlay components providing the confidentiality
service could leak the relevant keys, but it could still be
useful nonetheless. (BTW, I've no idea if it'd make sense
to have such a service that's separated from whatever
technology is used to move the VM or not.)

So I was wondering: will the wg actually define such a
confidentiality service or not? The response is that yes, 
this'll be considered for the requirements documents 
which is fine.

Note that I'm not trying to insist on a "yes" answer, even
though I think that'd be good. Even a "maybe, and that'll
be answered in the requirements specs before we re-charter"
would be ok. But regardless of the answer, I think it'd be
good to at least note this issue in the security
considerations section.

- 4.1, bullets: I found the use of ingress/egress
non-intuitive here. You mean ingress to the underlay and
egress from the underlay, right? It'd be good to explicitly
say that, though I figured it out eventually (or not, if
I'm wrong above:-)
Ted Lemon Former IESG member
No Objection
No Objection (2013-06-27 for -03)
Minor nit:
   While an overlay-based approach may address some of the
   "pain points" that were raised in ARMD (e.g., better support for
   multi-tenancy).  Analysis will be needed to understand the scaling
   tradeoffs of an overlay based approach compared with existing
   approaches. 

I think you want a comma between these two chunks; otherwise it doesn't really parse.

In 5.7, trill-fine-labeling is in the RFC editor queue, so I think that should be described as completed work, rather than something TRILL is investigating.

In general this draft is very clearly written, and does a good job of analyzing the problem space.   Thanks for doing such a good job on it!