[dns-operations] knot-dns

Warren Kumari warren at kumari.net
Mon Dec 15 17:22:09 UTC 2014

On Sun, Dec 14, 2014 at 5:47 PM, David Conrad <drc at virtualized.org> wrote:
> Hi,
> I'm having a bit of trouble believing this isn't April 1.
> On Dec 14, 2014, at 10:38 AM, Florian Weimer <fw at deneb.enyo.de> wrote:
>>> While it sounds good on phosphor, the concept of code diversity is so
>>> abstract, compared to the significant operational challenges and
>>> associated security challenges of operating separate systems
>>> performing the same functions (sort of), but differently, that any
>>> potential benefit is generally outweighed by the negative impact to
>>> security posture of said challenges.
> Sorry, this is simply wrong.
> A monoculture invites catastrophic failure. We've seen this over and over again.
> Sure, there are a wide variety of other possible failure points, but it would be simply insane to (say) have everyone run the exact same code base would mean that everyone is subject to the same Packet-of-Death.
> Are you seriously arguing that it is better to have your entire infrastructure subject to a PoD because it's a bit more challenging to run different software bases?
>> In particular, running different implementations behind a load
>> balancer on the same public IP address can break EDNS detection by
>> resolvers, and crafted queries sent to a resolver can make data
>> unavailable to that resolver (until a timeout occurs).
> Huh?
> If you're running multiple implementations behind a load balancer and one is not following the protocol specifications such that it breaks EDNS detection, the answer is to fix the broken resolver or run a different resolver that responds correctly, not run an identical code base.

.... or run a different load-balancing algorithm. There are multiple
ways to do this, but having the load-balancer hash only on src ip and
dst ip means that you should have the same client hitting the same

Then again, it all depends on why you are running a load-balancer - a
number of which become very sad with lots of short UDP sessions, and
fall over way before a raw server. If you are "load-balancing" to
optimize uptime, a nice options is:


Each of ns[1-4].example.com is a different IP and is "load-balanced"
behind a router.  Each of the instances contains multiple machines,
and each machine announces that fact that it is alive and answering
queries by announcing itself into OSPF (with e.g ospfd and a tiny
health-check script).

ns1 run BIND and NSD. The BIND boxes announce themselves into OSPF
with a cost of 10, the NSD boxes announce themselves with a cost of
ns2 run NSD and knot. The NSD boxes have a cost of 10, the knot a cost of 100
ns3 run yadifa and BIND. The yadifa have a cost of 10, the BIND 100.
ns4 run NSD and BIND. The NSD cost 10, the BIND 100.

OSPF doesn't do equal cost, and so the "primary" name server software
at each location gets all the traffic, unless it fails, at which time
the backup takes over. There can be multiple of the same type machine
at each location, routers are more than happy to ECMP down 16 paths
with no issue.

There is a small Python script that takes zone serving information and
outputs the correct stanzas for each nameserver type, and
[puppet|chef|ansible|salt|rsync|nfs|ssh] to propagate to all the
Built basically this at multiple places. You need a few extra boxes,
but they are a: cheap and b: used for other stuff when not primary.

"A host is a host from coast to coast
But no one will talk to a host that's close
Unless of course the host that's close is busy, hung, or dead."
    - sung to the Mr Ed tune.


> Regards,
> -drc
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I don't think the execution is relevant when it was obviously a bad
idea in the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair
of pants.

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