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  1. #1
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    VPS nameserver IP question

    Assume a VPS that runs as a webserver and ns1. Also assume that you have a secondary nameserver, ns2, on a separate VPS.

    If the VPS with the webserver and ns1 goes down, is any advantage gained by having had ns2 on a separate VPS? Does the ns2 help with caching mail? Doe the ns2 make the webserver/ns1 VPS accessible more quickly when it comes back online?


    Thanks.
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  2. #2
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    1.Nope, because the content is also hosted on VPS1. The only advantage of cluster nameservers is that if on fails, the other takes it's place.
    2.When VPS1 is down?(I didn't really understand this question)
    3.When a server goes down, when it is restarted and has all it's services running, it can be accessed instantly. Nameservers don't play any part in the speed of access after reboot. At least not in the way you're reffering to.

  3. #3
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    Ok it all makes sense now, thanks.
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  4. #4
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    Quote Originally Posted by rangy View Post
    Assume a VPS that runs as a webserver and ns1. Also assume that you have a secondary nameserver, ns2, on a separate VPS.

    If the VPS with the webserver and ns1 goes down, is any advantage gained by having had ns2 on a separate VPS? Does the ns2 help with caching mail? Doe the ns2 make the webserver/ns1 VPS accessible more quickly when it comes back online?
    There is an advantage with email. A big one.

    Nameservers are queried in no particular order, so either ns1 or ns2 could be queried any time a browser is looking to visit a site on your server. If the browser's request isn't answered because ns1 is unavailable, it looks for the one of the other nameservers.

    If no nameservers are available the response is that the site simply doesn't exist, and email is "bounced" back to the recipient with a message like "destination doesn't exist". It looks like your site either never existed or has closed down.

    What happens if you have a nameserver on a separate server, and it responds? That site on the server that has crashed still cannot be displayed in the browser, of course, but the return message is different. And email being sent to that server is queued for delivery later. So people sending email to your server don't get a "hey, that person doesn't exist or has fled town with all your money" type of message, but get a "mail delivery delayed" type of message.

    How long does the mail wait to be delivered? It depends on the SENDING email system, but its typically between 4 and 24 hours.

    So, in short, yes it does matter, especially for email.

  5. #5
    Quote Originally Posted by fshagan View Post
    There is an advantage with email. A big one.

    Nameservers are queried in no particular order, so either ns1 or ns2 could be queried any time a browser is looking to visit a site on your server. If the browser's request isn't answered because ns1 is unavailable, it looks for the one of the other nameservers.

    If no nameservers are available the response is that the site simply doesn't exist, and email is "bounced" back to the recipient with a message like "destination doesn't exist". It looks like your site either never existed or has closed down.

    What happens if you have a nameserver on a separate server, and it responds? That site on the server that has crashed still cannot be displayed in the browser, of course, but the return message is different. And email being sent to that server is queued for delivery later. So people sending email to your server don't get a "hey, that person doesn't exist or has fled town with all your money" type of message, but get a "mail delivery delayed" type of message.

    How long does the mail wait to be delivered? It depends on the SENDING email system, but its typically between 4 and 24 hours.

    So, in short, yes it does matter, especially for email.
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  6. #6
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    Quote Originally Posted by fshagan View Post
    So people sending email to your server don't get a "hey, that person doesn't exist or has fled town with all your money" type of message, but get a "mail delivery delayed" type of message.
    I like that description!

    Quote Originally Posted by rangy View Post
    Doe the ns2 make the webserver/ns1 VPS accessible more quickly when it comes back online?
    Anecdotal evidence only but yes, I believe it does. When I used the old "both nameservers on one machine" system I used to get clients reporting failed lookups on average about once a month. A quick server reboot or network glitch would cause lookup failure on a domain at the client's ISP lasting for up to an hour or so. Just adding a second nameserver in a different location, with no other changes, all but eliminated these events.

    What seems to happen is that with some ISP resolvers, if they find that all your nameservers are unreachable, they stop trying for a period of time. Effectively they're caching the failed lookup. Some say they shouldn't do this but from a resource-management point of view it makes perfect sense - resolvers are expected to fetch a result and then cache it for future requests. If they don't get a result, that would mean that they need to go out to all the authoritative nameservers again on the next request, only to fail again, and again on the next request, and so on.
    Last edited by foobic; 04-13-2011 at 09:55 AM.
    Chris

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  7. #7
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    Quote Originally Posted by ARPLink View Post
    The only advantage of cluster nameservers is that if on fails, the other takes it's place.
    Not so. As has been explained in later posts, having multiple nameservers in two or more locations has numerous benefits for mail delivery, browser error messages, and caching at IPSs etc.

    RFC2182 is actually quite a good read - Especially Section 3

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