Questions about anycasting setup

Fri Mar 9 09:55:08 UTC 2012

On 03/09/2012 01:34 AM, Elmar K. Bins wrote:
> Re Bill,
>
> woody at pch.net (Bill Woodcock) wrote:
>
>>> Well, let's say, using Quagga/BIRD might not really be best practice for
>>> everybody... (e.g., *we* are using Cisco equipment for this)
>> How does your Cisco know whether an adjacent nameserver is heavily loaded, and adjust its BGP announcements accordingly?
> It doesn't have to.
>
> I don't know how you guys do it, but we take great care to
> keep min. 70% overhead capacity during standard operation.
>
My point had to do with resilience in the face of hardware/OS/software
failures in the box providing the
service.  Bill's has more to do with resilience in the face of other
network events (e.g. the upstream for one
of the boxes has a DDOS; you cannot reasonably provide enough excess
capacity to handle that...)  Neither of these is addressed by using a
separate router to announce the server's anycast route.  (unless somehow
the Cisco is providing the anycasted service, which would address my
concern but still not Bill's.)

Also, Bill is probably talking root (or bigger public) servers whose
load comes from "off-site"; the average load characteristics for those
are well known but there can be extremes that would be hard to plan for
(hint - operating at 30% isn't really good enough, probably not 10%
either.  Bill (and the other Bill) have pretty good stats for this that
I've only glanced at...)  And it is easy to see where one of the
extremes might hit only one or two of the anycast instances.  He implies
having the instances talking to each other in background to adjust bgp
announcements to maybe help level things.  Fortunately at least for the
root servers, the redundancy is at two levels and anycast is only one of
them.

-- Pete