Is it possible to obtain all of the ip addresses correspoding to aFQDN?

Discussion in 'Linux Networking' started by Hongyi Zhao, Oct 18, 2015.

  1. As I understand it, for you there domain name encompasses host name. A host name
    is also a domain name. For some people a
    distinction is nice, and the word "domain name" differs in that a domain
    name normally implies that there are a number of host names associated
    with it, and a hostname refers (usually) to a single computer/ip, while
    a domain name encompasses a whole buch of host names. Anyway, that was
    the sense in which I interpreted the term "domain name". If it is not
    the sense in which the OP used the term, I apologize.
    Getting bogged down in semantics rarely leads to fruitful discussions.
    William Unruh, Oct 19, 2015
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  2. Hongyi Zhao

    Joe Pfeiffer Guest

    It isn't that a domain name is necessarily also a host name, it's that
    the RFC allows it to be. You may prefer that administrators never have
    a host with the same name as the domain, but that isn't going to stop
    them from doing it.
    Joe Pfeiffer, Oct 19, 2015
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  3. No I am saying that a host name is necessarily also a domain name, seems
    to be that point of the dispute.
    You mean like which is a host name and which is also a host name.

    I am willing to accept that is both a hostname and a
    domain name, but is a host name only. The
    interpretation of RFC1034 appears to be that is also
    a domain name. Not can be, but is.
    William Unruh, Oct 19, 2015
  4. Hongyi Zhao

    Rick Jones Guest


    rick jones
    Rick Jones, Oct 19, 2015
  5. Hongyi Zhao

    Lew Pitcher Guest

    It is (to me) easier to understand the domain name system if I divorce it
    from "host"s and "IP address"es.

    RFC1034 describes names as abstract entities, analogous (to me) to file

    Think of the /usr unix path hierarchy, for instance.
    is a pathname. The thing that
    describes has (or lacks) certain attributes (filesize, permission bits, etc).
    That it has (or lacks) these attributes doesn't invalidate the designation
    of /usr as a pathname.

    But, under this, there is more
    is also a pathname. The thing that
    describes has (or lacks) certain attributes (filesize, permission bits, etc).
    That it has (or lacks) these attributes doesn't invalidate the designation
    of /usr/local as a pathname.

    Additionally, that
    is a pathname doesn't invalidate
    as a pathname either.

    And so on, through

    Each step results in a pathname, and a node that has (or lacks) certain

    Similarly, the Domain Name System defines a "pathname", which they call
    a "domain name". Each refinement of "domain name" results in another "domain
    name". And, each "domain name" has (or lacks) certain attributes (mail
    exchanger, IP address, Chaosnet address, Hesiod address, etc).

    is a domain name, which lacks most attributes (including IP address). And
    is a domain name, which has multiple IPV4 addresses, a single IPv6 address,
    and multiple mail exchanges. And
    is /also/ a domain name, and also has multiple IPV4 addresses, and a single
    IPv6 address.

    Lew Pitcher, Oct 20, 2015
  6. Hongyi Zhao

    Baho Utot Guest

    You might hear the term Fully Qualified Domain Name (FQDN) and become
    confused because that term seems to imply that something like is a domain name instead of a hostname.
    I think that the term should have been called Fully Qualified Domain
    Hostname or maybe Fully Qualified DNS Name, because in the FQDN term,
    Domain Name doesn't mean "domain name" like, it means
    "the name on the domain", so the term can be misleading, although its
    used in many official documents and program descriptions just by rote.

    On the public part of the Internet, we all utilize a DNS infrastructure
    that use global top level domains like .com, .net, .org, .us, .fr, etc.
    Then people can purchase or accquire domains on those gTLDs such as Then we often see hostnames like or used under that. These are actually called logical
    hostnames because usually they are just names pointing at a single host.
    Often times the host they are pointing to has its own hostname called
    whatever the owner wants to call it, like

    Probably a lot of the confusion came about because some web hosting
    companies started calling hostnames like subdomains,
    where they are not. is only a sub domain if there
    are DNS records underneath it, like

    For the most part, you can simply follow this rule "domains encapsulate
    hostnames". Most people don't need to think about what DNS zones are,
    just leave that to DNS administrators. Resources on the network
    generally don't care or even know what their hostnames are or what
    hostnames might be pointing to them. They are mostly there for human
    reference and ease of use of the network.

    For example, the hostname refers to a World Wide Web
    server named "www" in the domain (the network associated with
    the Toyota automotive company). The hostname refers to
    an FTP server named "ftp" on Stanford University's local network (the

    hostname is the name given to the end-point (the machine in question)
    and will be used to identify it over DNS if that is configured
    domain is the name given to the 'network'
    it will be required to reach the network from an external point
    (like the Internet)

    It is usually written in the form, -- for example

    If you are in (say) a college campus named called 'The-University',
    and its domain is called '',
    a machine on the campus network called 'mymachine' would be addressed
    as, ''.

    If you were trying to connect to this machine from your home network,
    you would address it with that full name.
    The domain part would reach you to the campus network
    and the hostname would let you reach the exact machine in the campus.
    I am avoiding the details of IP Addressing and gateways here.
    Baho Utot, Oct 20, 2015
  7. Of course this is confused by a couple of things. Sometimes a "domain
    name" is also a host name. is an example. The name points
    to a specific host, but also is a subdomain -- is an
    example of another host.

    Also sometime what are host names actually point to a
    huge bunch of IP addresses, which are round-robined by the routers.
    PING ( 56(84) bytes of data.
    PING ( 56(84) bytes of data.

    So it is ia bit of a mess.
    William Unruh, Oct 21, 2015
  8. Hongyi Zhao

    Jorgen Grahn Guest

    I'm a bit confused: didn't we learn upthread that it /is/ a domain
    name, as defined by the RFCs? That all the names in DNS are domain

    Jorgen Grahn, Oct 21, 2015
  9. Hongyi Zhao

    Baho Utot Guest

    Not really,

    To be more specific, names that are in DNS are host names. Why would
    you be looking for a domain ( it should not respond ) when it is a host
    you want to connect to.

    This is what DNS was designed for, looking up a host from a "name". So
    you don't need to remember the IP for that host. Without DNS you would
    need to keep all the hosts you want/like to connect to in your
    /etc/hosts file and that would be gruesome.

    As I said before blame the web folks for messing this up as in web
    domain is not equal to tcp/ip domain.
    Baho Utot, Oct 21, 2015
  10. Hongyi Zhao

    Baho Utot Guest

    It shouldn't be if you are a sane network admin.
    Yes for load balancing
    No giant mess
    Baho Utot, Oct 21, 2015
  11. Hongyi Zhao

    Marc Haber Guest

    Jorgen is right, you're wrong. DNS only talks about domain names.
    You're confusing domains, zones and hosts.

    How would a domain "respond"? Only hosts can respond.

    Nobody stops you from assigning a domain name to a host, though. This
    is what we usually do. You're confusing this.
    DNS was designed to store and look up some kinds of data for domain
    names. The vast majory of lookups look up IP addresses for domain
    names, followed by looking up the domain name of name servers for a
    given domain, and looking up the domain name of mail exchangers for a
    given domain.
    Right, but looking up the IP address associated with a host's domain
    name is only one of the things that DNS is useful.
    There is no such thing as a "web domain", and there is no such thing
    as a "tcp/ip domain".

    Marc Haber, Oct 22, 2015
  12. Hongyi Zhao

    Baho Utot Guest

    You really need to go read the RFC which some why, what, when and where
    DNS came into existenca
    No you are confusing that
    No consult the RFCs for DNS
    Are you a web developer? If not that explains it
    Baho Utot, Oct 23, 2015
  13. Hongyi Zhao

    Jorgen Grahn Guest

    Didn't we do that once already?

    RFC 1034

    The domain name space is a tree structure. Each node and leaf on
    the tree corresponds to a resource set (which may be empty). The
    domain system makes no distinctions between the uses of the
    interior nodes and leaves, and this memo uses the term "node" to
    refer to both.

    Each node has a label, which is zero to 63 octets in length. [...]

    The domain name of a node is the list of the labels on the path
    from the node to the root of the tree. By convention, the labels
    that compose a domain name are printed or read left to right, from
    the most specific (lowest, farthest from the root) to the least
    specific (highest, closest to the root).

    I don't know how that could have been stated more clearly. If this
    doesn't help, the discussion is hopeless and I'll leave it with no
    further comments.

    It's true that "domain name" has other, informal meanings[0], but then
    it needs to be stated clearly that we're talking about one of those:
    talking about different things using overlapping names is a great way
    of getting nothing done.


    [0] And I admit that I was confused by that, before whoever-it-was
    quoted the RFC upthread (thank you!).
    Jorgen Grahn, Oct 23, 2015
  14. Hongyi Zhao

    Marc Haber Guest

    I am ignoring your other insults, knowing that I am right. There is no
    point in discussing things with people who dont want to learn.

    I'd rather have you show me one RFC that defines what a "web domain"
    is, just for the laughs. I am ready to apologize in case you should
    find one.

    Marc Haber, Oct 23, 2015
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