[*] History of DNS Root Anycast Controversy

Sean Walberg sean at ertw.com
Wed Jun 7 08:28:26 CDT 2006


I've been going through a couple of the presentations referenced on the page
and from searching NANOG.  Wicked stuff.

Keeping state was my big concern.  One paper explains the whole
configuration well:

Building Nameserver Clusters with Free Software
http://www.nanog.org/mtg-0505/abley.cluster.html

Each server in a single cluster speaks a routing protocol to the router to
advertise its availability.  This router then has multiple /32 routes to the
service address which it can perform equal cost load balancing.  The
document points out that routers should be keeping the same path for each
flow (source/dest IP pair) which is easily doable.

But what I really couldn't get was how to ensure that one transaction always
goes to the same cluster, given multiple clusters.  If the AS Path goes and
changes (ie failed link between providers), its possible that the user will
get sent to a different cluster.

Best Practices in IPv4 Anycast Routing
http://www.sanog.org/resources/sanog5-woody-anycast-v10.pdf

has a slide talking about the statefulness.  The implication of the slide
(p39) is that "it shouldn't matter, your application should deal with it".
The interesting part is the last point:

"Limited operational data shows underlying instability to be on
the order of one flow per ten thousand per hour of duration."

ie, the Internet is stable enough.

A bit of Googling led me to http://www.isoc.org/briefings/020/ which has
some commentary on the need for anycast dns and other gory details of the
DNS system.  Then there's
http://www.cs.ucla.edu/~vpappas/p/ss_sigmet05.pdf"On the use of
Anycast in DNS" which takes a brief look.

Finally, I was curious as to how distributed these clusters were, ie if I
could see different clusters from my different peers.

I peer with Allstream and Sprint in Toronto, and GT and Sprint in Winnipeg.
Using the F root server (192.5.5.241) as an example, the three providers all
peer with AS30130 which is a Toronto based network of ISC, and then AS3557
which is ISC in California who originates the 192.5.5.0/24 prefix.

Sean

On 6/6/06, Bill Reid <billreid at shaw.ca> wrote:
>
> This is the page I was talking about at tonight's meeting. Interesting
> commentary on the development of a new protocol.
>
> http://www.av8.net/IETF-watch/DNSRootAnycast/History.html
>
> As always it was an interesting meeting. Thanks to Sean and John for
> presenting
> and to all who came out and participated in the lively discussion.
>
> -- Bill
> _______________________________________________
> Asterisk mailing list
> Asterisk at muug.mb.ca
> http://www.muug.mb.ca/mailman/listinfo/asterisk
>
>


-- 
Sean Walberg <sean at ertw.com>    http://ertw.com/
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