[dns-operations] Too Open (Was: OpenDNS makes your Internet work better

Brad Knowles brad at stop.mail-abuse.org
Fri Jul 14 17:27:30 UTC 2006

At 2:47 PM +0200 2006-07-14, Per Heldal wrote:

>  So, unicast sites never go pear-shaped? That's new to me ;)

No, I'm sure they go pear-shaped all the time.  The point is that you 
are preventing the possibility of having all advertised routes 
collapse onto a single pod, and therefore if that single pod were to 
go down, you'd still have some other routes advertised to other 
(unicast-only) sites.

In other words, cut across first, then down.

>  Statistically a properly maintained anycasted IP service provide better
>  reliability than unicast.

Statistically, if airplanes were 99% reliable, you'd have multiple 
major airliners going down with hundreds of people dying on them 
every day.

>                        Thus, adding unicast-servers as you suggested
>  earlier may cause performance-degredation for those request that go to
>  the unicast destination.

The DNS already has algorithms for detecting which site is responding 
fastest, and strongly preferring those over the other sites.  You 
only need the unicast sites as backups, not for primary operations.

>                      Given that you can't prioritise one NS instance
>  over another, does it really make sense to add unicast hosts if you
>  already have multiple anycasted hosts?

Yup.  I'm a belt-and-suspenders kind of guy.  I don't care how good 
your suspenders are, or how many of them you've got, if the clips 
come off the pants (or the buttons they're attached to become 
detached from the pants) then you're going to need something else to 
hold them up -- unless you don't mind being seriously embarrassed 
(and possibly arrested for public lewdness), when they fail.

Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

  Founding Individual Sponsor of LOPSA.  See <http://www.lopsa.org/>.

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