North American Network Operators Group

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Re: ultradns reachability

  • From: Edward B. Dreger
  • Date: Fri Jul 02 01:24:30 2004

CLM> Date: Fri, 02 Jul 2004 04:18:07 +0000 (GMT)
CLM> From: Christopher L. Morrow

[ editted for brevity -- some punctuation/wording modified ]


CLM> So, I thought of it like this.  Rodney/Centergate/UltraDNS
CLM> knows:

[ snip enumeration ]


CLM> [and] should know almost exactly when they have a problem
CLM> they can term 'critical'...

One essentially has a DNS network on top of IP network.  Looks
like O(N) with centralized monitoring, although it could approach
O(N^2) if each server/pod cross-monitored all the others.


CLM> The problem then becomes the "Hey, .org is dead!" From where
CLM> is it dead?  What pod are you seeing it dead from? Is it
CLM> routing TO the pod from you?  FROM the pod to you? The pod
CLM> itself? Stuck/stale routing information somewhere on the
CLM> path(s)? This is very complex, or seems to be to me :(

I find your perception of complexity ironic.  Yes, there's a good
deal of splay.  However, I suspect a network the size of UU also
has a fair amount of peering splay, with a couple downstreams
thrown in for good measure. ;-)

However, I agree anycast has additional design implications:

* Should servers/pods talk among themselves using mcast along
  pairs that follow L3 topology?  Should N servers/pods each
  communicate with (N / 2 + 1) others, ignoring L3 topology?
  Fast poll the former and slow poll the latter?

* If servers/pods communicate among themselves, should they use
  unicast addresses? anycast addresses? anycast addresses
  tunneled through unicast?

* Each pod a stub?  Each pod interconnected with an OOB OAM
  network?  All pods interconnected with sizable backbone?  Does
  multicast serve a purpose?


Eddy
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