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  • What is the purpose of mDNS

    From George at Clug@21:1/5 to All on Sat Aug 3 11:00:02 2024
    Hi,


    What is the purpose of mDNS ? 


     It seems to be for multicast?  


    Does that mean its usage would be to say send video to a group of
    workstations all at the same time?  Like a corporate wide message
    from the CEO?  


    What other use?  


    It does not seem to be a unicast DNS system. That is a DNS system to
    find the IP address of a singular workstation/device on the network?


     https://en.wikipedia.org/wiki/Multicast_DNS
    By default, mDNS exclusively resolves hostnames ending with the .local top-level domain. This can cause problems if .local includes hosts
    that do not implement mDNS but that can be found via a conventional
    unicast DNS server. Resolving such conflicts requires
    network-configuration changes that mDNS was designed to avoid.


    https://wiki.archlinux.org/title/Avahi#Hostname_resolution
    2.1.1 Configuring mDNS for custom TLD
    The mdns_minimal module handles queries for the .local TLD only. Note
    the [NOTFOUND=return], which specifies that if mdns_minimal cannot
    find *.local, it will not continue to search for it in dns,
    myhostname, etc.


    https://www.ncsc.gov.ie/emailsfrom/Shadowserver/DoS/mDNS/
    DNS listens on port 53/UDP while mDNS listens on port 5353/UDP. DNS
    primarily uses point-to-point (unicast) communication with each DNS
    query sent to a specific IP address while mDNS uses
    point-to-multipoint (multicast) communication with the mDNS query sent
    to each devices on the local area network with the reserved mDNS
    multicast IPv4 address of 224.0.0.251.


    George.

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    <body><div>Hi,</div><div><br></div><div>What is the purpose of mDNS ?&nbsp;</div><div><br></div><div>&nbsp;It seems to be for multicast?&nbsp;&nbsp;</div><div><br></div><div>Does that mean its usage would be to say send video to a group of workstations
    all at the same time?&nbsp; Like a corporate wide message from the CEO?&nbsp;&nbsp;</div><div><br></div><div>What other use? &nbsp;</div><div><br></div><div>It does not seem to be a unicast DNS system. That is a DNS system to find the IP address of a
    singular workstation/device on the network?</div><div><br></div><div>&nbsp;https://en.wikipedia.org/wiki/Multicast_DNS<br>By default, mDNS exclusively resolves hostnames ending with the .local top-level domain. This can cause problems if .local includes
    hosts that do not implement mDNS but that can be found via a conventional unicast DNS server. Resolving such conflicts requires network-configuration changes that mDNS was designed to avoid.</div><div><br></div><div>https://wiki.archlinux.org/title/Avahi#
    Hostname_resolution<br>2.1.1 Configuring mDNS for custom TLD<br>The mdns_minimal module handles queries for the .local TLD only. Note the [NOTFOUND=return], which specifies that if mdns_minimal cannot find *.local, it will not continue to search for it
    in dns, myhostname, etc.</div><div><br></div><div>https://www.ncsc.gov.ie/emailsfrom/Shadowserver/DoS/mDNS/<br>DNS listens on port 53/UDP while mDNS listens on port 5353/UDP. DNS primarily uses point-to-point (unicast) communication with each DNS query
    sent to a specific IP address while mDNS uses point-to-multipoint (multicast) communication with the mDNS query sent to each devices on the local area network with the reserved mDNS multicast IPv4 address of 224.0.0.251.</div><div><br></div><div>George.<
    </div></body></html>

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  • From [email protected]@21:1/5 to George at Clug on Sat Aug 3 11:30:01 2024
    On Sat, Aug 03, 2024 at 06:56:42PM +1000, George at Clug wrote:
    Hi,


    What is the purpose of mDNS ? 


     It seems to be for multicast?  

    It is not /for/ multicast IP, it /uses/ multicast for name resolution.
    In a nutshell [1], it sends a "DNS" request to the local network asking
    "who is called Fritz here?", and Fritz answers with its IP. So sys-non-
    admins don't have to set up a name server.

    It is part of Microsoft's promise that anyone can be sysadmin because
    no one is. And then you end up in The Cloud(TM), which doesn't work either.

    Does that mean its usage would be to say send video to a group of workstations all at the same time?  Like a corporate wide message
    from the CEO?  

    No. In this case you use multicast IP to transfer videos. No relation
    among both except that multicast IP is the transport.

    Cheers

    [1] https://en.wikipedia.org/wiki/MDNS
    --
    t

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  • From George at Clug@21:1/5 to All on Sat Aug 3 12:40:01 2024
    Thanks for your comments, Tomas and Jeremy.

    George


    On Saturday, 03-08-2024 at 19:43 jeremy ardley wrote:


    On 3/8/24 17:26, [email protected] wrote:
    It is not/for/ multicast IP, it/uses/ multicast for name resolution.
    In a nutshell [1], it sends a "DNS" request to the local network asking "who is called Fritz here?", and Fritz answers with its IP. So sys-non- admins don't have to set up a name server.

    To amplify on that, it is used in situations where there is no DHCP server.

    IPv4 clients will then automatically assign themselves an address from 169.254.X.X/16 range (X.X is derived from the MAC address)

    They then multicast their hostname and IP address to everyone else on
    the LAN using mDNS.

    It is not a Microsoft only standard. It is defined in RFC 3927, "Dynamic Configuration of IPv4 Link-Local Addresses."

    It is used on a wide variety of hosts including Linux.



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  • From Darac Marjal@21:1/5 to All on Sat Aug 3 23:40:01 2024
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    <div class="moz-cite-prefix">On 03/08/2024 21:08, Lee wrote:<br>
    </div>
    <blockquote type="cite" cite="mid:CAD8GWssvk5RmZ9gbhLRK7W8j3m0hvv=[email protected]">
    <pre class="moz-quote-pre" wrap="">On Sat, Aug 3, 2024 at 6:51 AM George at Clug wrote:
    </pre>
    <blockquote type="cite">
    <pre class="moz-quote-pre" wrap="">
    Hi,

    What is the purpose of mDNS ?
    </pre>
    </blockquote>
    <pre class="moz-quote-pre" wrap="">
    "zero-configuration networking" seems to be the search term
    eg - <a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/Bonjour_(software)">https://en.wikipedia.org/wiki/Bonjour_(software)</a>

    </pre>
    <blockquote type="cite">
    <pre class="moz-quote-pre" wrap=""> It seems to be for multicast? </pre>
    </blockquote>
    <pre class="moz-quote-pre" wrap="">
    no, it _uses_ multicast.

    &lt;rant&gt; when did "utilize" replace "use"? &lt;/rant&gt;</pre>
    </blockquote>
    <p>It didn't. According to
    <a class="moz-txt-link-freetext" href="https://grammarist.com/grammar/use-vs-utilize/">https://grammarist.com/grammar/use-vs-utilize/</a>, they have similar
    but distinct meanings. The clearest explanation appears to be this
    paragraph: "Use the word <em>utilize when you</em> are using
    something beyond its original and intended purpose. You may use a
    bat to play baseball, but you can utilize it as a self-defense
    tool. "</p>
    <p>So, in technical terms, saying that "application X utilizes Y"
    could actually be seen as disparagement. mDNS "uses" multicast
    networking because multicast networking is a general-purpose tool.
    But to say that mDNS utilises multicast networking would seem to
    suggest that the developers of mDNS had to work around the design
    of multicast networking - that they had to work against multicast.<br>
    </p>
    <br>
    </body>
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  • From David Wright@21:1/5 to [email protected] on Tue Aug 6 07:00:01 2024
    On Sat 03 Aug 2024 at 11:26:38 (+0200), [email protected] wrote:
    On Sat, Aug 03, 2024 at 06:56:42PM +1000, George at Clug wrote:
    What is the purpose of mDNS ? 

     It seems to be for multicast?  

    It is not /for/ multicast IP, it /uses/ multicast for name resolution.
    In a nutshell [1], it sends a "DNS" request to the local network asking
    "who is called Fritz here?", and Fritz answers with its IP. So sys-non- admins don't have to set up a name server.

    It is part of Microsoft's promise that anyone can be sysadmin because
    no one is. And then you end up in The Cloud(TM), which doesn't work either.

    Isn't that what modern networking is striving to attain?

    “It is not practical to expect home users to configure their networks.
    Thus, the assumption of this document is that the homenet is as far
    as possible self-organising and self-configuring, i.e., it should
    function without proactive management by the residential user.”

    (RFC 7368)

    “Users and devices within a home network (hereafter referred to as
    "homenet") require devices and services to be identified by names
    that are unique within the boundaries of the homenet [RFC7368]. The
    naming mechanism needs to function without configuration from the
    user. While it may be possible for a name to be delegated by an ISP,
    homenets must also function in the absence of such a delegation.
    This document reserves the name 'home.arpa.' to serve as the default
    name for this purpose, with a scope limited to each individual
    homenet.”

    (RFC 8375)

    Cheers,
    David.

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  • From [email protected]@21:1/5 to David Wright on Tue Aug 6 08:10:01 2024
    On Mon, Aug 05, 2024 at 11:49:37PM -0500, David Wright wrote:
    On Sat 03 Aug 2024 at 11:26:38 (+0200), [email protected] wrote:

    [...]

    It is part of Microsoft's promise that anyone can be sysadmin [...]

    Isn't that what modern networking is striving to attain?

    Whoever "modern networking" is :-)

    (thanks for the RFCs, BTW)

    I think this is one of those "make people smarter" vs. "make tools
    smarter" things. It is interesting, utterly complex (because it
    mixes technical and social issues), and the "optimum" isn't even
    well-defined, and in itself a moving target.

    I seem to fit nigh to the "make people smarter" side of the current
    situation.

    Cheers
    --
    t

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  • From gene heskett@21:1/5 to [email protected] on Tue Aug 6 10:30:01 2024
    On 8/6/24 02:04, [email protected] wrote:
    On Mon, Aug 05, 2024 at 11:49:37PM -0500, David Wright wrote:
    On Sat 03 Aug 2024 at 11:26:38 (+0200), [email protected] wrote:

    [...]

    It is part of Microsoft's promise that anyone can be sysadmin [...]

    Isn't that what modern networking is striving to attain?

    Whoever "modern networking" is :-)

    (thanks for the RFCs, BTW)

    I think this is one of those "make people smarter" vs. "make tools
    smarter" things. It is interesting, utterly complex (because it
    mixes technical and social issues), and the "optimum" isn't even well-defined, and in itself a moving target.

    I seem to fit nigh to the "make people smarter" side of the current situation.

    There is a hell of an echo here Tomas, but smarter has not arrived yet,
    dumber has the stage.

    balenaetcher is purported to be smart enough to write an .iso and make
    it bootable. But no surprise, I dl the latest version and run it, select
    the iso file and it refuses to proceed to selecting the target device to
    write it to. So I'm back to using dd. I even try XFBurn, but get told by
    it that burn has not been enabled yet. WTH good is a space wasting file
    called XFBurn that has not grown a bun routine in close to a decade?

    But each new boot attempt by an armbian img seems to first expand the filesystem which it then apparently uses to skip the unperformed root
    and use pw creations, so every time the card is subsequently booted that
    is all skipped, going directly to a user login which has at this point
    not yet been created.

    So it needs a fresh .img write for everytime the card is inserted in a
    bpi-m5. Top that off by bookworm's k3b which now cannot see any file to
    burn it to a dvd+rw disk, so I am blocked from creating a bootable dvd.
    Color me disgusted.

    Cheers

    Cheers, Gene Heskett, CET.
    --
    "There are four boxes to be used in defense of liberty:
    soap, ballot, jury, and ammo. Please use in that order."
    -Ed Howdershelt (Author, 1940)
    If we desire respect for the law, we must first make the law respectable.
    - Louis D. Brandeis

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