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NETMAN  2013

NETMAN 2013

Subject:

Re: DNS, multiple forwarders, and multiple paths

From:

Kevin Wilcox <[log in to unmask]>

Reply-To:

The EDUCAUSE Network Management Constituent Group Listserv <[log in to unmask]>

Date:

Fri, 29 Mar 2013 11:43:04 -0400

Content-Type:

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On Thu, Mar 28, 2013 at 09:11:33PM -0700, Mark Duling wrote:

>    Well at the least I'd say OSPF or anycast isn't something we'd do soon,
>    because we're still building out redundancy in our core infrastructure and
>    such, and we're not even at our own planned ideal point with DNS as we'd
>    planned it out a couple of years ago.  We do have redundant DNS of course
>    (actually Infoblox).

Putting on the flame suit because this is going to go over like a lead
balloon...

The whole idea of secondary and tertiary servers is that you assign
the closest or most robust server as primary to a specific group, with
servers *at disparate geographic locations* as secondary and tertiary.
When the primary becomes unavailable operating systems should go to
their secondary and then tertiary servers. "Unavailable" may be a
timeout due to the server being down, it might be a dropped linked or it
may just be high latency and responses not making it back in time - all
of which are signals to modern operating systems to move on down their
list.

Some operating systems go a step further by sending a query to ALL DNS
servers they have available and using the response from the first reply.
It makes for a little burst of chit-chat early on but it works - and they
usually "latch on" to the fastest of the group until it becomes
unavailable or their network connection is reset so that chatter really
is just early on.

Technologies like ANYCAST are great for passing out ONE IP instead of
three or four but, really, I see it as adding unnecessary complexity to
a relatively elegant system - if you want to have disparate servers,
deploy disparate servers and pass them out in the order you want
specific groups to use them. The management is a LOT simpler than
deploying ANYCAST (but not nearly as "cool", so I get that).

Unless you're Google, or offering DNS services to hundreds of thousands
of users across the globe, in which case ANYCAST (or similar) deployment
is simple compared to the other challenges you're facing.

kmw

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**********
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