Subject: [dnssd] Comments on the current mDNS/DNS-SD drafts

From: "Hosnieh Rafiee" <[email-masked]>
Date: Mon, 21 Apr 2014 16:33:23 +0200

Hello,

I finally finished writing a  threat model for mDNS, I will post the link
after my co-author and the 3 other volunteer contributors  have a chance to
review this document. 
Since I needed to read all the RFCs and document related to mDNS and DNS-SD,
I found a few typos or have a few comments that the authors might find them
useful to consider. 

--------------------------------------------------------
draft-bhandari-dnssd-mdns-gateway-00

section 3.2 : applied repeated twice

section 3.8.1 responseas ->  responses

section 3.8.1
Does wireless devices mean the devices with constraint resources? So, mDNS
does not work for a laptop or similar devices without any movement? I am
asking this question because a person can use a laptop at work while he is
sitting at his desk at his office without the need to move from one place to
another but he might use WLAN to connect to the office network.
I guess while someone is moving, he would never consider the use of, a
printer or most of available resources during his movement, I cannot myself
move and type or click on something even on my mobile phone. But he might
consider using a WLAN. However, in this scenario, he prefers not to change
his service from one WLAN to another. In other words, he'd like to receive
continuous service without any disconnection. If this is true, then mDNS
really does not work for mobility scenario or is not useful ( I might be
wrong but I guess considering mobility is only extra effort without any
special benefit). Probably the authors can show otherwise by adding more
useful mobility scenario that shows the usefulness of service discovery
during mobility.
In other words, for the mDNS gateway or devices, it is not really important
whether the node is in subnet A or subnet B or moving from subnet A to B. I
do not also think that you move a server or printer from one place to
another place while other nodes are using their resources... other physical
limitation like electricities, etc. avoids such scenario. This is why again,
IMHO, considering mobility does not make sense in mDNS.

Section 3.8.2
The first sentence is not true. Again the example of laptop in my last
paragraph or the example of looking up for a printer while you're moving..
you will never do it. You first find a place to take a sit and then you try
to lookup resources on the network.

Another comment:
Where is the location of mDNS device?  How it knows which client is not in
this network anymore? Isn't it by actively sending something like keep alive
message? If this is true, then this process might lead to large network
traffic. If not, then how it knows when the client is leaving?

Two dots at the end of sentence after "network"

Section 3.8.3
Again a node that provides a service usually doesn't move and it might be a
client that moves.

--------------------------------------------------

Draft-ietf-dnssd-requirements

Section 1.2 terminology
Is mDNS a transport layer protocol? I guess the authors mean mDNS is an
application layer protocol that uses UDP like DNS as a transport layer.

Section 2.3 For low power nodes there should be more requirements since they
cannot load a large service discovery lists (memory constraints) and they
need to only rely on the two first entry of the list . They cannot also wait
for a long time since it consumes a lot of energy. 
---------------------------------------------------

draft-otis-dnssd-mdns-xlink-02

section 2.5

second paragraph: The solution for automation is only windows-based and not
compatible to 90% of DNS servers. 

Best,
Hosnieh

---

From: Douglas Otis <[email-masked]>
Date: Tue, 22 Apr 2014 12:44:05 -0700

Dear Hosnieh,

Thank you for your feedback. I am about to finish my draft regarding mDNS as well.  While many directly assign keys to systems rather than utilizing Kerberos, neither Kerberos or LDAP are primarily used by Windows.  The goal of the document was to assist in efforts at moving a link-local scheme into either a multi-link home or corporate.  In these environments, distributed keys would be fairly risky.

Regards,
Douglas Otis

On Apr 21, 2014, at 7:33 AM, Hosnieh Rafiee <[email-masked]> wrote:

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---

From: "Hosnieh Rafiee" <[email-masked]>
Date: Wed, 23 Apr 2014 07:54:25 +0200

Dear Douglas,

> 
> Thank you for your feedback. I am about to finish my draft regarding mDNS
as
> well.  While many directly assign keys to systems rather than utilizing
> Kerberos, neither Kerberos or LDAP are primarily used by Windows.  The
goal
> of the document was to assist in efforts at moving a link-local scheme
into
> either a multi-link home or corporate.  In these environments, distributed
> keys would be fairly risky.
> 

Yes, I understand. Thanks for the clarification.

Best,
Hosnieh