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DNS Racing - providing services using Multi ISP, Load balancing, Fail over.

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  1. #11

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    HKFoot,

    See below about round robin....

    You want you can use ZTE or Cisco or Juniper or Arista... with DNS racing...

    I wish I was selling fish balls, maybe more people would be able grasp that.

    Shir, HKfoot and All the other "BUT IT IS ROUND ROBIN"

    There is NO round robin. Each server will serve you the same IP each time...
    It is most likely that onece you get the IP you will
    keep on going through the same IP for days or even for ever depending how far you
    are from the network. Users shoudl hopefully split into both circuits.


    I can see why you guys think this is round robin with the mail2, mail3 and mail4.
    Those records will not be alternated between I only put them there in case a
    user wants to specify where htye want to connect whether it is directly
    to either path or one or simply go on the other path what ever it might be regardless
    of whethere it is up or not....

    Anyway, I am taking a point that all you guys thing is round robin and I am
    going to remove the mail2, 3, and 4 in the initial document.



    protocl,
    Sorry I am not going to bother replying your post as there are JUST too many things
    that are just nonsense.


    100LL, yes DNS 101... though, it is not documented or seen anyone else use it...
    Maybe other people came up with the same idea... but no one has bothered to
    document it. I am doing that, with the hope that people out there can have
    faster bigger, more reliable internet connectivity without haivng to buy any
    fancy hardware or get into the complexities of BGP and AS numbers....

    This is something that anyone can implemet.



    FOR THOSE THAT STILL DON"T GET IT.
    Picture this you go into a restaurant and there are two waiters, you call
    "waiter", the fastest/closes waiter responds. You keep using that waiter until
    you fancy.... until his shift is over. And that is how DNS Racing works...


  2. #12

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    Shri,
    DNS queries are sent to all 5 NS servers at the same time. That is how the
    DNS system works (nothing to do with DNS racing)

    It is not a case of one NS server and then the next... Ok?

    (side note: Yes if DNS did work like you say you would get a round robin effect on
    DNS Racing)

    GeoDNS, I recall your hacked bind Maxmind thing you introduced me to what you were
    using... There is a HUGE flaw in that.... in that countries fibers backbones ASs etc
    have little to do with Geography. Also you have no clue if when you send a user
    to their local server they have a valid routing path over to your "local" web
    site.

    I frequently see problems accessing CDN.GEOCLICKS.COM and now or it stalls
    loading the page...

    If you want to use a database to drive traffic it would have to be far smarter
    than just using the country code... We could come up with very sexy AS/BGP
    based responses.... still it would not solve the problem
    that you have no clue IF the user can acctually access the server that you are
    sending them to... on the other hand DNS Racing would be able to avoid that
    situation...

    If you can't get the DNS reply from the DNS server it means that you don't have
    routing and access that server or resource, you will get another IP to a destination
    where you can access the content or service. WOW! Rocket science!

    You could implement DNS Racing by placing each of your DNS servers with the each
    of the CDN that it serves... and be done with all GeoDNS crap. We users don't
    care if our HK pages load from Brazil as long as they load fast.


    DNS Racing does have the problem that IF you are using a DNS resolver outside the
    AS number you re in it could result in not being sent to the optimal path and
    you lose the ability to fail over to what ever path is available... Well just
    like the Internet works now, and Shri's GeoDNS.


    Showed what I wrote to the BIND user group - ISC. Initially drew
    lots of cricism, seems to have calmed down, lots of alarmist rejection which
    later on was proven wrong. One guy came up with an improvement,
    but I better not go into it.


    I am not trying to sell you anything here... If someone wants to do it the
    idea is out there, free.... You can use it when you have a limited budget or you have massive server farm or you have multiple CDN's like shrii does...

    It has worked for us for years.. We will soon be deploying on our new website.

    PS. Shri, 3rd party MX, Google Apps, next you will be doing ladyboys in wan
    chai, (oh whoops the secret is out!)

    Last edited by Fenix2; 01-06-2011 at 03:26 AM.

  3. #13

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    sorry by cdn.geoclicks.com = meant c4.geoclicks.net aka Amazon cloudfront.


  4. #14

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    >> DNS queries are sent to all 5 NS servers at the same time. That is how the DNS system works (nothing to do with DNS racing)

    Was not aware of that. Seems like a waste of bandwidth if that happens and very inefficient. I'll trust you on this one.

    I'm not worried about you trying to sell me anything. Got no money..

    I don't use the GeoDNS thing ... don't have multiple ISPs and multiple country related data centers. The point of that was you can send different results to people based on their CIDRs. Over time you can create your own customized CIDR table dynamically based on response times etc etc etc ...


  5. #15

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    >> DNS queries are sent to all 5 NS servers at the same time. That is how the DNS system works (nothing to do with DNS racing)

    Was not aware of that. Seems like a waste of bandwidth if that happens and very inefficient. I'll trust you on this one.

    ( Edit: Confirms what I thought was the case from the days I used to write TCP related code in DOS: http://serverfault.com/questions/227...ns-query-works )

    Second, the local nameserver then chooses one of the nameservers from the list returned by h.root-servers.net and sends the same query: "what is the A record for www.google.com?" In this case the nameserver queried was f.gtld-servers.net (192.35.51.30). f.gtld-servers.net, which is authoritative for .com, has responded with the nameserver delegations for the zone google.com
    Still.. I could be wrong.

    I'm not worried about you trying to sell me anything. Got no money..

    I don't use the GeoDNS thing ... don't have multiple ISPs and multiple country related data centers. The point of that was you can send different results to people based on their CIDRs. Over time you can create your own customized CIDR table dynamically based on response times etc etc etc ...
    Last edited by shri; 01-06-2011 at 07:48 AM.

  6. #16

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    This also seems to indicate there is a DNS server selection algorithm.

    Re: Bind algorithm for Name server selection


  7. #17

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    Was also able to find this:

    http://www.ijicic.org/09-0761-1.pdf

    In order to enhance availability, robustness and reliability, each domain is usually served
    by multiple DNS name servers. These IP addresses are the items contained in the NS
    resource records, which could be obtained and cached by a local DNS server [2]. When
    there is a query for this domain, the local DNS server chooses one from the cached NS
    records to forward the query via some criterion, which is referred to as the DNS server
    selection (see Figure 1).
    So, still don't understand why a client would query multiple DNS servers for an IP address. Seems very very inefficent, given that most of these protocols were designed to work over slow ... very very very slow links.

  8. #18

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    My post was mainly based on Cisco Systems equipment and configurations vs. your Multi-vendor DNS-Racing/Load balancing/dual ISP redundancy.
    Since it's Cisco, may be that's Why you do not understand? Load balance per packet via dual Physical and/or Logical Interfaces. Simple.

    Last edited by protocl; 01-06-2011 at 10:11 AM. Reason: Add.

  9. #19

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    Quote Originally Posted by shri:
    Was also able to find this:

    http://www.ijicic.org/09-0761-1.pdf



    So, still don't understand why a client would query multiple DNS servers for an IP address. Seems very very inefficent, given that most of these protocols were designed to work over slow ... very very very slow links.
    If you look for DNS resolvers and servers for Windows I think there is one called INA or INA plus it has a 30 day trial. It has very nice tool built which allows you to see the DNS cache and queries going out. You can get to see a lot about DNS efficiency in some registries... At least before .com.hk domains needed one or two more DNS recursions than .hk.com

    Why query multiple DNS servers?

    If you start from scratch to crawl the web from any of the ISPs I love so much, you will find out that going to the root servers, querying the DNS servers etc... is around 450ms average (or that is what we came with), that includes timing out for

    DNS packets are minute, and what matters is that you are given the IP as fast as possible.... and that you are not faced with time outs. The DNS resolver has no clue which one of the DNS server is UP, which one has the lowest latency, so going sequentially through them makes little sense. When DNS was designed, the Internet was even slower and had higher latencies.... and there was even less of a reason to go sequentially.

    So this wastage makes sense..... doing it differently would be inneficient in terms of time and would bring overall reliablity down by a lot as applications would time out. Imagen you had 5 DNS servers and your resolver has to query them in sequence and the first 2 DNS servers are down.... it would take a long time to get an IP.

    Most DNS queries we had was 64KB/s, which is a bit of queries, still the DNS traffic is minute, considering that they are cached and that resolver will not be asking more questions for a considerable amount of time.

    The resolver *client* code in unix (not bind, this is part of the OS) which looks at resolve.conf is archaic and that is certainly sequential.... ie it will ask DNS resolver server sequentially. Still when the query hits a DNS resolver it will send out queries to all NS servers.

  10. #20

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    >> Why query multiple DNS servers?

    Going back to the original post on DNS racing...

    It should be a question of "if standard clients and servers query multiple servers concurrently and respond to the first request". I think it is most likely going to be query the first server and then the next.

    Given that NS records are handed to the "client" (the client could be your ISPs DNS server) in random order, random DNS servers will be queried and random routes will be assigned.

    I can fully understand high volume environments with specialized DNS requirements and the need for high speed concurrent resolution.

    May be I'm slow .... but I don't get the whole racing around a round robin thing.