DNS Info

Discussion in 'Cisco' started by Toby, Dec 4, 2004.

  1. Toby

    Toby Guest

    Hi

    I am in the process of applying for an internal job within my company.

    Part of my job if successful would be to diagnose, advise and repair
    customer IP routing problems which encompase various layer 2 technologies,
    Although some of these such as VPDN using L2TP are fairly new to me. I have
    no real problem with the rest (as yet).

    Another part of the job and my reason for this post is based on DNS and
    Email which I have not had any dealing with as part of my current role.

    I appreciate that this may be behond the spoke of this group but also
    believe that being an active member of this group and that it is a related
    subjet you may help.

    At present my understanding of DNS/Email can be summarised as such.

    1) DNS is an hirearchial database.
    2) A device will normally point to a DNS server's IP address (called server
    A) and if the server A does not know where the end device lives it will know
    at least a root servers address and will ask that.
    e.g. www.mypages.toby.org

    3) Server A will ask the root server where where www.mypages.toby.org lives
    which the root server would not know, but would know of another server(s)
    that would, namely the .org servers.

    4) Server A would then ask the .org servers the same question and would get
    a simular reply with the address of another server say 1234.org.

    5) The above would continue until a definitive IP address could be resolved
    and delivered to the original machine.

    I am under the impression that the above is dealt with with what is known as
    A records.

    Another element is MX records.

    My current understanding is that when we send emails the email server
    requests for a DNS lookup of the email address domain name i.e after the @
    and uses a lookup called the MX record. This lookup returns the name of the
    Mail server responsible for the recipricant and a further lookup of the DNS
    A reference using the above returns in the same manner with the IP address
    of where to deliver the mail.

    Any extra info / web links would be usefull. Also not mentioned above is
    email relays/ reverse DNS etc. I have used google to the extreme hence the
    above

    Regards

    Toby
    Toby, Dec 4, 2004
    #1
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  2. Toby

    Erik Freitag Guest

    On Sat, 04 Dec 2004 21:46:34 +0000, Toby wrote:

    > Hi
    >
    > I am in the process of applying for an internal job within my company.
    >
    > ... Another part of the job and my reason for this post is based on DNS
    > and
    > Email which I have not had any dealing with as part of my current role.
    >
    > I appreciate that this may be behond the spoke of this group but also
    > believe that being an active member of this group and that it is a
    > related subjet you may help.


    I recommend comp.protocols.dns.bind, I think Barry Margolin contributes to
    this group as well, and he has a lot of DNS mojo. Look for the O'Reilly
    bok DNS and BIND (4th edition) by Liu and Albitz - kind of the bible for
    DNS workings and DNS management. Lots of information at www.isc.org as
    well as many other websites.

    >
    > At present my understanding of DNS/Email can be summarised as such.
    >
    > 1) DNS is an hirearchial database.
    > 2) A device will normally point to a DNS server's IP address (called
    > server A) and if the server A does not know where the end device lives
    > it will know at least a root servers address and will ask that.
    > e.g. www.mypages.toby.org
    >
    > 3) Server A will ask the root server where where www.mypages.toby.org
    > lives which the root server would not know, but would know of another
    > server(s) that would, namely the .org servers.
    >
    > 4) Server A would then ask the .org servers the same question and would
    > get a simular reply with the address of another server say 1234.org.
    >
    > 5) The above would continue until a definitive IP address could be
    > resolved and delivered to the original machine.
    >
    > I am under the impression that the above is dealt with with what is
    > known as A records.
    >
    > Another element is MX records.
    >
    > My current understanding is that when we send emails the email server
    > requests for a DNS lookup of the email address domain name i.e after the
    > @ and uses a lookup called the MX record. This lookup returns the name
    > of the Mail server responsible for the recipricant and a further lookup
    > of the DNS A reference using the above returns in the same manner with
    > the IP address of where to deliver the mail.


    I don't see anything wrong with your understanding, but I have a feeling
    you're going to need a lot more depth if you're managing a large DNS
    configuration. You'll need to understand how domain name servers
    communicate with one another, security practices, zone transfers,
    delegation, dynamic updates, how to make changes to the Internet's
    view of your authoritative name servers, maybe how to build a DNS, maybe
    how to format the configuration files, rules for where and when certain
    types of records can be used, and more.

    > Any extra info / web links would be usefull.


    I would start with www.isc.org and follow the BIND links.

    > Also not mentioned above is
    > email relays/ reverse DNS etc. I have used google to the extreme hence
    > the above


    Read the Liu and Albitz book - everything you need to get going is there.
    Erik Freitag, Dec 4, 2004
    #2
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  3. Toby

    Toby Guest

    "Erik Freitag" <> wrote in message
    news:p...
    > On Sat, 04 Dec 2004 21:46:34 +0000, Toby wrote:
    >
    >> Hi
    >>
    >> I am in the process of applying for an internal job within my company.
    >>
    >> ... Another part of the job and my reason for this post is based on DNS
    >> and
    >> Email which I have not had any dealing with as part of my current role.
    >>
    >> I appreciate that this may be behond the spoke of this group but also
    >> believe that being an active member of this group and that it is a
    >> related subjet you may help.

    >
    > I recommend comp.protocols.dns.bind, I think Barry Margolin contributes to
    > this group as well, and he has a lot of DNS mojo. Look for the O'Reilly
    > bok DNS and BIND (4th edition) by Liu and Albitz - kind of the bible for
    > DNS workings and DNS management. Lots of information at www.isc.org as
    > well as many other websites.
    >
    >>
    >> At present my understanding of DNS/Email can be summarised as such.
    >>
    >> 1) DNS is an hirearchial database.
    >> 2) A device will normally point to a DNS server's IP address (called
    >> server A) and if the server A does not know where the end device lives
    >> it will know at least a root servers address and will ask that.
    >> e.g. www.mypages.toby.org
    >>
    >> 3) Server A will ask the root server where where www.mypages.toby.org
    >> lives which the root server would not know, but would know of another
    >> server(s) that would, namely the .org servers.
    >>
    >> 4) Server A would then ask the .org servers the same question and would
    >> get a simular reply with the address of another server say 1234.org.
    >>
    >> 5) The above would continue until a definitive IP address could be
    >> resolved and delivered to the original machine.
    >>
    >> I am under the impression that the above is dealt with with what is
    >> known as A records.
    >>
    >> Another element is MX records.
    >>
    >> My current understanding is that when we send emails the email server
    >> requests for a DNS lookup of the email address domain name i.e after the
    >> @ and uses a lookup called the MX record. This lookup returns the name
    >> of the Mail server responsible for the recipricant and a further lookup
    >> of the DNS A reference using the above returns in the same manner with
    >> the IP address of where to deliver the mail.

    >
    > I don't see anything wrong with your understanding, but I have a feeling
    > you're going to need a lot more depth if you're managing a large DNS
    > configuration. You'll need to understand how domain name servers
    > communicate with one another, security practices, zone transfers,
    > delegation, dynamic updates, how to make changes to the Internet's
    > view of your authoritative name servers, maybe how to build a DNS, maybe
    > how to format the configuration files, rules for where and when certain
    > types of records can be used, and more.
    >
    >> Any extra info / web links would be usefull.

    >
    > I would start with www.isc.org and follow the BIND links.
    >
    >> Also not mentioned above is
    >> email relays/ reverse DNS etc. I have used google to the extreme hence
    >> the above

    >
    > Read the Liu and Albitz book - everything you need to get going is there.


    Excellent just the kind of food for thought I'm after

    Toby
    Toby, Dec 5, 2004
    #3
  4. In article <_eqsd.3489$>,
    Toby <> wrote:
    :Another part of the job and my reason for this post is based on DNS and
    :Email which I have not had any dealing with as part of my current role.

    Some of the other newsgroups might be more appropriate, such as
    comp.protocols.tcp-ip . Mostly, though, this is stuff you would look
    up in man pages and books such as the O'Reilley series.


    :At present my understanding of DNS/Email can be summarised as such.

    :1) DNS is an hirearchial database.

    Well, sort of, but I'd be more comfortable if you included
    the adjective 'distributed' in there; and even then it'd be
    a semantic question as to whether it qualifies as a database or not.


    :2) A device will normally point to a DNS server's IP address (called server
    :A) and if the server A does not know where the end device lives it will know
    :at least a root servers address and will ask that.
    : e.g. www.mypages.toby.org

    Before it would ask a root server, it would look in its own tables,
    lobbing left-most components off of the name until it found
    a match. For this purpose, the root servers aren't particularily
    special: they are just pre-filled entries that happen to match against
    the end-of-name marker. It is not mandatory to have root cache
    entries: if you don't, then an unknown name will climb to the top
    of the internal tree and when it doesn't find useful information,
    it will return a "Never heard of it!" response.

    Whether a DNS server will ask another system for assistance is optional
    behaviour, usually controlled by a flag named 'recursive'. It is
    considered perfectly acceptable to only succeed in answering queries
    for domains you have direct answers for, never making reference to
    another server. Indeed, it is not uncommon for well-known
    companies to have a public DNS server that only answers questions
    about the company's domain, and a private DNS server for internal
    use that will ask outside systems. By configuring like that, one
    can avoid ending up acting as a DNS cache server for the rest of
    the net -- your machine using its resources to do queries that
    other [outside] machines could easily do for themselves.


    :3) Server A will ask the root server where where www.mypages.toby.org lives
    :which the root server would not know, but would know of another server(s)
    :that would, namely the .org servers.

    The root servers are handed the FQDN query and proceed with the
    component-climbing behaviour themselves -- they don't just go
    directly to the 'org' server. I used to think the root server
    was just handed the top-level query (e.g., 'org'), but I have seen
    enough cases now where manually chasing just top level queries ends
    up in lots of cross-references of servers all denying they know
    anything authoritative. Being handled the FQDN query is the
    behaviour that matches the experimental evidence.


    :4) Server A would then ask the .org servers the same question and would get
    :a simular reply with the address of another server say 1234.org.

    :5) The above would continue until a definitive IP address could be resolved
    :and delivered to the original machine.

    :I am under the impression that the above is dealt with with what is known as
    :A records.

    That's a slight simplification, in that there are a number of other
    important resource record types, not just IP information. Behind the
    scenes, SOA records are important for house-keeping caches. And
    not behind the scene at all, PTR records are crucial for answering
    the question "Given this IP address, what is the name of that system?".
    Also, it isn't necessarily the case that what the client gets back is
    the target record itself: it might instead get back a NS (nameserver)
    record and be expected to query that nameserver. [This happens a lot.]


    :Another element is MX records.

    :My current understanding is that when we send emails the email server
    :requests for a DNS lookup of the email address domain name i.e after the @
    :and uses a lookup called the MX record.

    Yes.

    :This lookup returns the name of the
    :Mail server responsible for the recipricant

    Not necessarily. It might return saying there is no MX record. In that
    case, the mail transfer agent (MTA) should look for the A record of
    the given domain and contact that location directly.

    :and a further lookup of the DNS
    :A reference using the above returns in the same manner with the IP address
    :eek:f where to deliver the mail.

    Potentially, but there is also a possible short-circuit. When a
    DNS server knows that one system is an MX for another, then it often
    knows the IP address of the mail handling system. The DNS server may
    then (and often does) optionally return the A record to save the
    client from looking it up [which could end up hitting the same DNS
    server with another query, making it go through all the setup and lookup
    all over again.]

    This same short-circuit strategy is commonly used when NS (nameserver)
    records are being returned; the optional records are referred to
    as 'glue' records. When a glue record is returned, then the client
    is supposed to trust the glue data rather than ignorning it and looking
    the information all up again. That's not just an efficiency issue: there
    is some reasoning involved about which system is likely to have
    authoratative information.


    :Any extra info / web links would be usefull. Also not mentioned above is
    :email relays/ reverse DNS etc. I have used google to the extreme hence the
    :above

    Read the O'Reilley books! Even if you just go into a bookstore and skim
    a few chapters without buying, you'll be much further ahead. Some of
    the older books are available for free download, and some of the books
    are available to download for a fee.
    --
    "Meme" is self-referential; memes exist if and only if the "meme" meme
    exists. "Meme" is thus logically a meta-meme; but until the existance
    of meta-memes is more widely recognized, "meta-meme" is not a meme.
    -- A Child's Garden Of Memes
    Walter Roberson, Dec 5, 2004
    #4
  5. Toby

    John Smith Guest

    i believe an e version of dns&bind 4ed. can be found at
    alt.binaries.e-book.technical
    it was posted sometime in the last month or two.

    "Toby" <> wrote in message
    news:_eqsd.3489$...
    > Hi
    >
    > I am in the process of applying for an internal job within my company.
    >
    > Part of my job if successful would be to diagnose, advise and repair
    > customer IP routing problems which encompase various layer 2 technologies,
    > Although some of these such as VPDN using L2TP are fairly new to me. I
    > have no real problem with the rest (as yet).
    >
    > Another part of the job and my reason for this post is based on DNS and
    > Email which I have not had any dealing with as part of my current role.
    >
    > I appreciate that this may be behond the spoke of this group but also
    > believe that being an active member of this group and that it is a related
    > subjet you may help.
    >
    > At present my understanding of DNS/Email can be summarised as such.
    >
    > 1) DNS is an hirearchial database.
    > 2) A device will normally point to a DNS server's IP address (called
    > server A) and if the server A does not know where the end device lives it
    > will know at least a root servers address and will ask that.
    > e.g. www.mypages.toby.org
    >
    > 3) Server A will ask the root server where where www.mypages.toby.org
    > lives which the root server would not know, but would know of another
    > server(s) that would, namely the .org servers.
    >
    > 4) Server A would then ask the .org servers the same question and would
    > get a simular reply with the address of another server say 1234.org.
    >
    > 5) The above would continue until a definitive IP address could be
    > resolved and delivered to the original machine.
    >
    > I am under the impression that the above is dealt with with what is known
    > as A records.
    >
    > Another element is MX records.
    >
    > My current understanding is that when we send emails the email server
    > requests for a DNS lookup of the email address domain name i.e after the @
    > and uses a lookup called the MX record. This lookup returns the name of
    > the Mail server responsible for the recipricant and a further lookup of
    > the DNS A reference using the above returns in the same manner with the IP
    > address of where to deliver the mail.
    >
    > Any extra info / web links would be usefull. Also not mentioned above is
    > email relays/ reverse DNS etc. I have used google to the extreme hence the
    > above
    >
    > Regards
    >
    > Toby
    >
    >
    John Smith, Dec 5, 2004
    #5
  6. Toby,

    You seem to have the gist, no problems. What I did when I needed to get
    up to scratch on DNS was, download a copy of linux (I used knoppix -
    www.knoppix.net) and configured a box from the floor up to be a DNS
    server. At first at home, then I wrote a bigger one for one of our test
    labs.

    The man pages are very good and there are some very good books out
    there, such as O'Reiliys dns & bind. But there's nothing quite like
    getting your hands dirty and building one, with all the niggles along
    the way.

    Hope this is of some help.
    LH



    Toby wrote:
    > Hi
    >
    > I am in the process of applying for an internal job within my company.
    >
    > Part of my job if successful would be to diagnose, advise and repair
    > customer IP routing problems which encompase various layer 2 technologies,
    > Although some of these such as VPDN using L2TP are fairly new to me. I have
    > no real problem with the rest (as yet).
    >
    > Another part of the job and my reason for this post is based on DNS and
    > Email which I have not had any dealing with as part of my current role.
    >
    > I appreciate that this may be behond the spoke of this group but also
    > believe that being an active member of this group and that it is a related
    > subjet you may help.
    >
    > At present my understanding of DNS/Email can be summarised as such.
    >
    > 1) DNS is an hirearchial database.
    > 2) A device will normally point to a DNS server's IP address (called server
    > A) and if the server A does not know where the end device lives it will know
    > at least a root servers address and will ask that.
    > e.g. www.mypages.toby.org
    >
    > 3) Server A will ask the root server where where www.mypages.toby.org lives
    > which the root server would not know, but would know of another server(s)
    > that would, namely the .org servers.
    >
    > 4) Server A would then ask the .org servers the same question and would get
    > a simular reply with the address of another server say 1234.org.
    >
    > 5) The above would continue until a definitive IP address could be resolved
    > and delivered to the original machine.
    >
    > I am under the impression that the above is dealt with with what is known as
    > A records.
    >
    > Another element is MX records.
    >
    > My current understanding is that when we send emails the email server
    > requests for a DNS lookup of the email address domain name i.e after the @
    > and uses a lookup called the MX record. This lookup returns the name of the
    > Mail server responsible for the recipricant and a further lookup of the DNS
    > A reference using the above returns in the same manner with the IP address
    > of where to deliver the mail.
    >
    > Any extra info / web links would be usefull. Also not mentioned above is
    > email relays/ reverse DNS etc. I have used google to the extreme hence the
    > above
    >
    > Regards
    >
    > Toby
    >
    >
    Leigh Harrison, Dec 5, 2004
    #6
  7. Toby

    Toby Guest

    Thank you everyoune for your replies. I have decided to get a copy of Mr
    O'Reilly's book as everyone has recomended it.

    Thanks again

    Toby

    "Toby" <> wrote in message
    news:_eqsd.3489$...
    > Hi
    >
    > I am in the process of applying for an internal job within my company.
    >
    > Part of my job if successful would be to diagnose, advise and repair
    > customer IP routing problems which encompase various layer 2 technologies,
    > Although some of these such as VPDN using L2TP are fairly new to me. I
    > have no real problem with the rest (as yet).
    >
    > Another part of the job and my reason for this post is based on DNS and
    > Email which I have not had any dealing with as part of my current role.
    >
    > I appreciate that this may be behond the spoke of this group but also
    > believe that being an active member of this group and that it is a related
    > subjet you may help.
    >
    > At present my understanding of DNS/Email can be summarised as such.
    >
    > 1) DNS is an hirearchial database.
    > 2) A device will normally point to a DNS server's IP address (called
    > server A) and if the server A does not know where the end device lives it
    > will know at least a root servers address and will ask that.
    > e.g. www.mypages.toby.org
    >
    > 3) Server A will ask the root server where where www.mypages.toby.org
    > lives which the root server would not know, but would know of another
    > server(s) that would, namely the .org servers.
    >
    > 4) Server A would then ask the .org servers the same question and would
    > get a simular reply with the address of another server say 1234.org.
    >
    > 5) The above would continue until a definitive IP address could be
    > resolved and delivered to the original machine.
    >
    > I am under the impression that the above is dealt with with what is known
    > as A records.
    >
    > Another element is MX records.
    >
    > My current understanding is that when we send emails the email server
    > requests for a DNS lookup of the email address domain name i.e after the @
    > and uses a lookup called the MX record. This lookup returns the name of
    > the Mail server responsible for the recipricant and a further lookup of
    > the DNS A reference using the above returns in the same manner with the IP
    > address of where to deliver the mail.
    >
    > Any extra info / web links would be usefull. Also not mentioned above is
    > email relays/ reverse DNS etc. I have used google to the extreme hence the
    > above
    >
    > Regards
    >
    > Toby
    >
    >
    Toby, Dec 5, 2004
    #7
  8. Toby

    Erik Freitag Guest

    On Sun, 05 Dec 2004 02:09:43 -0500, John Smith wrote:

    > i believe an e version of dns&bind 4ed. can be found at
    > alt.binaries.e-book.technical
    > it was posted sometime in the last month or two.


    Is this legal? I'm in the US if that makes a difference.
    Erik Freitag, Dec 5, 2004
    #8
    1. Advertising

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