Re: [homenet] Status of draft-tldm-simple-homenet-naming CFA

[Toke Høiland-Jørgensen <[e-mail]>]

Ted Lemon <[e-mail]> writes:

> El 13 ag 2017, a les 11:49, Toke Høiland-Jørgensen <[e-mail]> va escriure:
>> In any case, the failure mode of getting a it wrong is a sub-optimal
>> path being chosen; but if ISP A's DNS server takes five seconds to
>> respond, we'd get a better result from just using the timely answer from
>> ISP B's and going over the suboptimal path to get to the content (in
>> many cases, at least).
>
> Not if the suboptimal path has substantially worse performance for the
> duration of the session.

Sure, it depends on the particular application (hence the "in many
cases" in my original statement)... My point is just that it's not an
obvious across the board win.

>> But only the client can make that coupling (from DNS reply to connection
>> attempt). So if we're just filtering the result set based on the address
>> the client uses (which is how I interpret what you put in the draft),
>> we're degrading the experience for any client that doesn't know how to
>> repeat the query from another source address. So we'd effectively be
>> requiring hosts to support MPvD; and we're not supposed to require host
>> changes, are we?
>
> Many hosts we care about already support MPvD because the companies
> that sell the software that runs on those hosts think it solves a
> useful problem.   Adding support for MPvD on the homenet is a
> relatively small change now that their stacks already support it.

Right, so we're adding it as an extra service for hosts that support it?
That is fine with me, but then it shouldn't be a requirement. I.e., we
can go "supporting MPvD is a good idea, and here is how you do it
correctly", rather than the current "must support" language.

> As for a "degraded experience," do you mean that if we select one
> upstream provider for a particular client, that's going to result in a
> degraded experience for the user?   Why would that be the case?

I mean that if we query all upstreams we get the best aggregate
performance from all available DNS servers. Whereas if we limit queries
to a particular ISP, we only get as good performance as that particular
ISP can provide. If that was going to be the best on anyway, fine. If
not, we are worse off by limiting queries to that ISP.

>> I can see how these scenarios make sense for a device that know the
>> types of connection (like a cell phone with cellular and WiFi links).
>> Less so in the home, where all the client sees are different prefixes;
>> in this case, either the network has to enforce policy (like the
>> failover scenario), or we'll have to communicate more information to the
>> hosts, which goes back to my point above about host changes...
>
> Yes, in order to make this work we have to communicate additional
> information to the host, and the host has to use it. That's why I
> described a fallback solution for hosts that don't support this. It's
> not clear that the solution I described is the right one, of course;
> the point of saying something there was to have a place where we can
> write whatever the advice is that we decide to give when we figure
> this out; what I described would work, but it's possible that an
> entirely RA-based solution would work just as well, in which case
> personally I'd prefer it.

How do non-MPvD-aware hosts react to an announcement of an MPvD-specific
DNS server? Does it ignore the server entirely, or does it ignore the
PvD information and use the server anyway?

>> Right, well, I'm not sure I have the energy to go argue with dnsop on
>> this one... :) But I can probably live with a mechanism where we just
>> specify that the user needs to have an option to override the default
>> behaviour (i.e., add their own DNS servers which take precedence over
>> whatever we end up specifying).
>
> That's fine with me!

Cool :)

-Toke