DNS anycast considered harmful (was: .ORG problems this evening)

Stephen J. Wilcox steve at telecomplete.co.uk
Thu Sep 18 13:16:10 UTC 2003


On Thu, 18 Sep 2003, Todd Vierling wrote:
> On Thu, 18 Sep 2003, Stephane Bortzmeyer wrote:
> 
> : > Still doesn't help .ORG, which is 100% anycast and thus has no DNS-based
> : > redundancy
> :
> : Wrong since there are two IP addresses. They may fail at the same time
> : (which apparently happened to you) but there is a least an element of
> : non-BGP redundancy (I'm not aware of any TLD running with only one
> : anycasted name server, although it would still have some redundancy).
> 
> Okay, let me qualify then:
> 
> "...no DNS-based redundancy when both routes point to the same place and
> that particular place goes off the air while its BGP advertisements stay
> up and running..."
> 
> DNS-based redundancy typically implies going to different servers at
> different locations, regardless of what BGP says.  The fact that anycast
> took me to the same place for both IPs, and that same place went down all at
> once, means that I was effectively looking at a single point of failure with
> no way for DNS to pick another place to look.

Okay but

1. Only you were affected
2. Only you have both servers going to the same place

Theres a theme in this, perhaps indicating where the problem may have been :)






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