RE: [nvo3] Last Call: <draft-ietf-nvo3-framework-06.txt> (Framework for DC Network Virtualization) to Informational RFC

Hi Brian,

Thanks for your comments. See my replies inline.

Marc 

> -----Original Message-----
> From: nvo3 [mailto:nvo3-bounces@ietf.org] On Behalf Of Brian 
> E Carpenter
> Sent: Saturday, May 24, 2014 10:46 PM
> To: ietf@ietf.org
> Cc: nvo3@ietf.org
> Subject: Re: [nvo3] Last Call: 
> <draft-ietf-nvo3-framework-06.txt> (Framework for DC Network 
> Virtualization) to Informational RFC
> 
> A few comments below. I can't help feeling that NVO3 is 
> creating a monster, however.

Hopefully not... The intent being to reuse as many existing solutions and to describe the actual gaps to offer a scalable DC solution.

> 
> > 4.1. Pros & Cons
> ...
> >           - Traffic carried over an overlay may not 
> traverse firewalls and
> >             NAT devices.
> 
> I don't know whether  "may not" means "might not" or "must 
> not", and that completely determines what the sentence means. 
> For example, does it mean this?
>        - Traffic carried over an overlay might fail to 
> traverse firewalls and
>          NAT devices.

Yes, it does. It will be changed accordingly.

> 
> I suggest reviewing every instance of "may not" to avoid this 
> ambiguity.

Ok.

> 
> >           - Hash-based load balancing may not be optimal as the hash
> >             algorithm may not work well due to the limited number of
> >             combinations of tunnel source and destination 
> addresses. Other
> >             NVO3 mechanisms may use additional entropy 
> information than
> >             source and destination addresses.
> 
> Load balancing appears out of nowhere here. Are we supposed 
> to assume that load balancing is a requirement? Load 
> balancing between what - between different tenants, different 
> physical DCs, different servers?

It is mentionned as one possible challenge. I agree this sentence is a bit out of place though.
Hence, I have no problem removing it. This is actually discussed in much more details in the dataplane requirements draft.

The text implied load balancing of TS traffic by NVEs over underlay paths.

> 
> Also, there seems to be an assumption that load balancing is 
> only based on addresses. Actually it's usually based on ports 
> as well, and more or less by definition they are invisible to 
> the underlay.
> So it's worse than "may not work well".

The text does mention that "additional entropy information" can be used. NVEs have such visibility before sending traffic over the underlay.

> 
> I would have expected QoS support to also appear as a 
> challenge, for similar reasons. Isn't giving tenants a fair 
> share of the underlay capacity an issue? (There's a mention 
> of traffic engineering later, but surely you don't want this 
> issue to be handled by operators twiddling knobs?)

Indeed. This is discussed in section 4.2.6.

> 
> > 4.2.4. Path MTU
> ...
> >        TCP will
> >        adjust its maximum segment size accordingly.
> 
> And how will that work for non-TCP traffic?

It is the while point of this section... It is either Path MTU discovery or IP fragmentation.

> 
> >        It is also possible to rely on the NVE to perform 
> segmentation and
> >        reassembly operations without relying on the Tenant 
> Systems to know
> >        about the end-to-end MTU. The assumption is that 
> some hardware
> >        assist is available on the NVE node to perform such 
> SAR operations.
> >        However, fragmentation by the NVE can lead to performance and
> >        congestion issues due to TCP dynamics and might require new
> >        congestion avoidance mechanisms from the underlay 
> network [FLOYD].
> 
> In a word: yuck. Surely you should be recommending against 
> anything like that, or any attempt to re-segment TCP on the fly.

This sentence needs some rewording as the last sentence (starting with "however") was meant to say that this is not a desirable solution.

> 
> >        Finally, the underlay network may be designed in 
> such a way that the
> >        MTU can accommodate the extra tunneling and possibly 
> additional NVO3
> >        header encapsulation overhead.
> 
> Surely you should be recommending this, which is by far the 
> safest solution. (And of course it should allow for the IPv6 
> minimum MTU.)

Agreed.

> 
> > 7. References
> ...
> >        [NVOPS] Narten, T. et al, "Problem Statement : 
> Overlays for Network
> >                  Virtualization", draft-narten-nvo3-overlay-problem-
> >                  statement (work in progress)
> 
> Nit: that draft was replaced a long time ago by 
> http://tools.ietf.org/html/draft-ietf-nvo3-overlay-problem-statement
> (which is already in the RFC Editor queue).

Ok

> 
>     Brian
> 
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