[mif] DNS selection with HE-MIF

[GangChen <[e-mail]>]

Hello all,

We would like to follow up the discussions on last IETF meeting.
We are asked to add the texts clarifying DNS selections using HE-MIF.
With the minutes and my memory, there are two cases HE-MIF failed to
help if DNS queries are sent out on multiple interfaces in parallel

Case 1: Mismatch of DNS answers with specific provisioning domain

A DNS answer may be only valid on a specific provisioning domain, but
HE-MIF may not be aware of that mapping because DNS answers may not be
kept with the provisioning from which the answer comes.

The thing would become worse if asking internal name with public
address response or asking public name with private address answers

Case 2: Some FQDNs can be resolvable only by sending queries to the
right server (e.g., intranet services). Otherwise, a response with
NXDOMAIN is replied.
HE-MIF would treat the DNS server with fast response as optimal only
if there is valid response.
That may cause chaos, since NXDOMAIN doesn't provide useful information.

Therefore, RFC6731 should be recommended as the proper solution for
DNS selections.

We are not sure if there is anything missing.
Authors would like to ask your kind check and comments. We will update
the draft accordingly if there are no further comments.

Best Regards

Gang