TCP/IP and DNS Questions - TCP-IP

This is a discussion on TCP/IP and DNS Questions - TCP-IP ; Ok, this is a pretty straight forward question for someone who knows tcp/ip and dns in windows environments. I have a argument going with one of my co-workers about the order in which dns requests are sent. Simply put, he ...

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  1. TCP/IP and DNS Questions

    Ok, this is a pretty straight forward question for someone who knows
    tcp/ip and dns in windows environments. I have a argument going with
    one of my co-workers about the order in which dns requests are sent.
    Simply put, he thinks when a dns request is sent, it is sent to the
    default gateway as well as the primary dns server at the same time and
    whichever responds first is the one that gets accepted. However, I'm
    under the impression and understanding that a gateway never accepts
    anything other than an IP address and when a dns request is made, it
    checks local cache and files first, then requests resolution from the
    primary dns server then down to other dns servers from there. Can
    someone that has extensive knowledge of how this work please chime in
    and let me know or link an article that explains this process
    thuroughly? We really need to settle this for business purposes. Thanks
    all.


  2. Re: TCP/IP and DNS Questions

    On 11 Aug 2006 06:49:01 -0700, "squiggie" wrote:

    >Ok, this is a pretty straight forward question for someone who knows
    >tcp/ip and dns in windows environments. I have a argument going with
    >one of my co-workers about the order in which dns requests are sent.
    >Simply put, he thinks when a dns request is sent, it is sent to the
    >default gateway as well as the primary dns server at the same time and
    >whichever responds first is the one that gets accepted. However, I'm
    >under the impression and understanding that a gateway never accepts
    >anything other than an IP address and when a dns request is made, it
    >checks local cache and files first, then requests resolution from the
    >primary dns server then down to other dns servers from there. Can
    >someone that has extensive knowledge of how this work please chime in
    >and let me know or link an article that explains this process
    >thuroughly? We really need to settle this for business purposes. Thanks
    >all.


    To my understanding the gateway is (DNS wise) not at all involved with
    answering DNS requests unless you configure it as being one of the DNS
    servers (or of course if said gateway at the same time is also your
    DHCP server and anounces itself as being your DNS server). Needless to
    say that if the gateway is counfigured as a DNS server it must either
    act like a proxy or it might be that you use a gateway machine which
    at the same time is also a DNS server.

    HTH

    Markus


  3. Re: TCP/IP and DNS Questions


    Markus Zingg wrote:
    > On 11 Aug 2006 06:49:01 -0700, "squiggie" wrote:
    >
    > >Ok, this is a pretty straight forward question for someone who knows
    > >tcp/ip and dns in windows environments. I have a argument going with
    > >one of my co-workers about the order in which dns requests are sent.
    > >Simply put, he thinks when a dns request is sent, it is sent to the
    > >default gateway as well as the primary dns server at the same time and
    > >whichever responds first is the one that gets accepted. However, I'm
    > >under the impression and understanding that a gateway never accepts
    > >anything other than an IP address and when a dns request is made, it
    > >checks local cache and files first, then requests resolution from the
    > >primary dns server then down to other dns servers from there. Can
    > >someone that has extensive knowledge of how this work please chime in
    > >and let me know or link an article that explains this process
    > >thuroughly? We really need to settle this for business purposes. Thanks
    > >all.

    >
    > To my understanding the gateway is (DNS wise) not at all involved with
    > answering DNS requests unless you configure it as being one of the DNS
    > servers (or of course if said gateway at the same time is also your
    > DHCP server and anounces itself as being your DNS server). Needless to
    > say that if the gateway is counfigured as a DNS server it must either
    > act like a proxy or it might be that you use a gateway machine which
    > at the same time is also a DNS server.
    >
    > HTH
    >
    > Markus


    So really, if your gateway isn't setup to be a DNS server and you have
    a seperate DNS server on your network, there isn't anyway a gateway
    (which is a router) would receive DNS requests, and for that matter
    forward DNS requests it receives out to the interent for lookup? That
    would be the responsibility of the DNS server to forward lookups to the
    internet.


  4. Re: TCP/IP and DNS Questions

    >So really, if your gateway isn't setup to be a DNS server and you have
    >a seperate DNS server on your network, there isn't anyway a gateway
    >(which is a router) would receive DNS requests, and for that matter
    >forward DNS requests it receives out to the interent for lookup? That
    >would be the responsibility of the DNS server to forward lookups to the
    >internet.


    Hmm, not sure if I undestand you correctly (english is not my native
    language), but if you have a DNS server within your network - or if
    you want on a second lan which is NOT routed through your default
    gateway and if this is the only DNS server you configure in your PC,
    then requests would be sent towards this (your own) DNS server which
    then is in charge of resolving the request propperly and no, in this
    scenario no single DNS request would be sent from your PC towards the
    default gateway.

    The default gateway is here to route IP packets whoes destination
    can't be found by checking all other known routes or which are not
    targeted towards the same network segment your PC is in. This is true
    independant of the protocol used on top of IP (including DNS). It
    would be a "local feature" of your PC's DNS resolver if it would send
    out aditional DNS queries towards the default gateway if it could not
    satisfy the request through the configured DNS servers. Not sure if
    Windows behaves like this but I don't think so.

    Actually you can very easily verify your PC's behaviour by installing
    Etheral on it ( www.ethereal.com ) and simply monitor all DNS traffic
    between your PC and the switch it is connected to. You then quickly
    see what's going on by simply exercising all configuration variants.

    HTH

    Markus


  5. Re: TCP/IP and DNS Questions

    On 11 Aug 2006, in the Usenet newsgroup comp.protocols.tcp-ip, in article
    <1155309998.148599.317200@74g2000cwt.googlegroups.c om>, squiggie wrote:

    >Markus Zingg wrote:


    >>"squiggie" wrote:


    >>> Ok, this is a pretty straight forward question for someone who knows
    >>> tcp/ip and dns in windows environments.


    OK, now watch it. Windoze has it's own concept of name server - the falsely
    labeled "WINS" which relates to local names within the work-group. This has
    nothing to do with _Internet_ name services.

    >>> I have a argument going with one of my co-workers about the order in
    >>> which dns requests are sent. Simply put, he thinks when a dns request
    >>> is sent, it is sent to the default gateway as well as the primary dns
    >>> server at the same time and whichever responds first is the one that
    >>> gets accepted.


    Is the default gateway running a name server? If not, the only thing you'd
    get from it is a FOAD packet in reply.

    >>> However, I'm under the impression and understanding that a gateway never
    >>> accepts anything other than an IP address and when a dns request is made,


    By who? Some host on your LAN? Or by some _client_ application running on
    the gateway.

    >>> it checks local cache and files first, then requests resolution from the
    >>> primary dns server then down to other dns servers from there.


    Unless the router is running a name server application, it rejects any
    requests TO IT to do name resolution.

    >> To my understanding the gateway is (DNS wise) not at all involved with
    >> answering DNS requests unless you configure it as being one of the DNS
    >> servers (or of course if said gateway at the same time is also your
    >> DHCP server and anounces itself as being your DNS server). Needless to
    >> say that if the gateway is counfigured as a DNS server it must either
    >> act like a proxy or it might be that you use a gateway machine which
    >> at the same time is also a DNS server.


    Agreed

    >So really, if your gateway isn't setup to be a DNS server


    End it right there. If it's not running a DNS server, it won't accept any
    requests for name service. The "conversation" would be something like

    CLIENT: What's the IP of foo.example.com
    GATEWAY: I don't do names - go away.

    That's pretty simple, isn't it? Notice the gateway doesn't ask any one
    else - that's not it's job. Computers don't do things on their own. They
    have to be told/configured to do things. Your gateway is configured to
    route packets. It _probably_ wasn't told that it has an _additional_ job
    of resolving names, any more than it was told to call for pizza when someone
    is hungry. Not configured means not going to be done.

    >and you have a seperate DNS server on your network, there isn't anyway a
    >gateway (which is a router) would receive DNS requests,


    Well... if someone screwed up the configuration on the _client_ (which
    could also be done by screwing up the configuration of a DHCP server),
    the _client_ may ask anyone it's been told is a name server for answers.
    Someone could have told you that you could ask me - but I'm not a name
    server, so I'll tell you not to bother me. That didn't stop you from asking
    in the first place.

    >and for that matter forward DNS requests it receives out to the interent
    >for lookup?


    No, the gateway isn't an errand boy - if you ask it about a name, it won't
    forward your requests or any thing similar. BUT IF YOUR CLIENT wants to ask
    a real name server out on the Internet, it addresses a DNS query to _that_
    name server, and sees that the way to _reach_ the name server is to send it
    via the gateway. The gateway will see that the packet (doesn't matter if
    it's a DNS query or an web page request) isn't _addressed_ to itself, but
    is meant for some host "out there" and it will forward the _packet_ to the
    next hop. The gateway has no reason to look into the packet to see what it
    is - it's job is to _forward_ packets as it's configuration tells it to.

    >That would be the responsibility of the DNS server to forward lookups to
    >the internet.


    In simple terms, yes. DNS is a massive referral service. A DNS server
    knows the address[es] of the root servers - ask them who to ask. Thus,
    a request to resolve example.sometown.k12.pa.us gets an initial response
    to ask mumble.fumble.us (address 198.18.1.10) who knows that TLD. In turn,
    the name server asks mumble.fumble.us, and is told that foo.bar.pa.us at
    address 198.18.34.46 knows about k12.pa.us - ask them. This goes on until
    the name server finds the right server to ask about example.sometown.k12.pa.us
    and so on.

    Old guy

  6. Re: TCP/IP and DNS Questions


    squiggie wrote:

    > Simply put, he thinks when a dns request is sent, it is sent to the
    > default gateway as well as the primary dns server at the same time and
    > whichever responds first is the one that gets accepted.


    What sense would it make to send a DNS request to something that's not
    a DNS server? And what sense would it make to, as a normal course of
    action, send the same request to two different places?

    A host that needs to convert a name to an IP address using DNS
    typically sends the request to the first of its configured DNS servers.
    If that DNS server does not reply (or sends back a failure), it will
    query the next configured DNS server.

    Gateways, unless they also happen to be DNS servers, do not perform DNS
    in the ordinary course of routing packets.

    DS


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