Subject: [Int-area] Review of draft-bonica-v6-multihome-02

From: Suresh Krishnan <[email-masked]>
Date: Wed, 15 Feb 2012 16:18:23 -0500

Hi authors,
  I read through this draft and I had a few questions/comments

Section 2.2.1:

What happens if the multiple CNBs are not of the same size? I believe
that the solution will still work, but it would be nice if the example
talks about the general case of different CNB sizes (Then the CNBs being
the same size will be a specific case).

Section 2.2.2:

I am entirely unconvinced that the following is true

"For any interface, the ratio of upper half to lower half assignments
roughly controls the portion of traffic arriving through each upstream
provider."

Please explain how this works for a host on an inside that initiates
connections.

(I do see how it works for servers accepting connections from the
outside though, perhaps using some form of DNS round robin techniques)

Section 2.5:

How does the routing inside the site work? In specific, it would be
useful to explain how packets from a host with addresses from each block
gets to the right translator. i.e. How does a host with a source address
in the lower half of the SAB know to send all outgoing packet to NPT#1?
If it sends it to NPT#2, uRPF will break on PE#2, right?

Future expansion:

I think the document should mention something about the sizing the SAB
in order to allow future changes. I would assume some sort of safety
margin would be useful. The way that it is specified in the document is
too rigid. e.g. In the case described in the document, what happens if
the site wants to add another upstream provider? Should it renumber?

Thanks
Suresh

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From: Ronald Bonica <[email-masked]>
Date: Fri, 17 Feb 2012 10:46:59 -0500

Suresh,

Thanks for this thoughtful review. Responses inline:

> Date: Wed, 15 Feb 2012 16:18:23 -0500
> From: Suresh Krishnan <[email-masked]>
> To: Internet Area <[email-masked]>
> Subject: [Int-area] Review of draft-bonica-v6-multihome-02
> Message-ID: <[email-masked]>
> Content-Type: text/plain; charset="ISO-8859-1"
> 
> Hi authors,

You are absolutely correct! The CNBs don't need to be the same size. Also, they don't need to be as large as the current version of the drafts says that they have to be. I will fix this in the next version of the draft. Look for a new version in the next few days.

> outside though, perhaps using some form of DNS round robin techniques)

Again, you are absolutely right. The statement above applies only to servers accepting connections from the outside. When a server initiates a connection, the source address that it chooses determine the path that return traffic will traverse. Again, I will fix this in the next version of the draft.

> If it sends it to NPT#2, uRPF will break on PE#2, right?

Because NPTv6 is stateless, and because all NPTs serving a sight are configured identically, a packet can leave the site through any NPT. Egress traffic doesn't need to traverse the same NPT as ingress traffic. 

In a typical environment, both CE routers advertise a default route into the site. Outbound traffic finds its way to one CE or the other. If the site wishes to do something more sophisticated, it can. Whatever the site chooses to do will work with NPTv6. I will make this clear in the next version of the draft.
> the site wants to add another upstream provider? Should it renumber?

This is a good idea and a natural consequence of your first comment. I will tackle this in the next draft version.

Thanks again for your thoughtful comments.

                           Ron