>
> From: bind-users-boun...@lists.isc.org
> [mailto:bind-users-boun...@lists.isc.org] On Behalf Of Harshith Mulky
> Sent: Tuesday, October 20, 2015 10:50 AM
> To: bind-users@lists.isc.org
> Subject: RE: bind-users Digest, Vol 2230, Issue 1
>
> No Mark, This is not a question I am asked to answer for some course
>
> We have an implementation where, once the DNS Servers are down, The Client
> (Our device) Blacklists the IP address of DNS Servers for some period of Time
> It can only whitelist the server when it receives periodic Responses to a
> NAPTR Request.
>
> What I did find was even though Our Client was able to send periodic NAPTR
> requests, we are unable to check what kind of NAPTR requests are sent out
Harshith, While I am new to the group I am not sure this is the right audience
for your question as it does not really pertain to bind or the DNS protocol.
Having said that I love a good puzzle and am curious so below are a couple
follow-up
questions.
1.) Are these devices some type of VoIP device? I've seen many novel DNS
based
scenarios used for VoIP before.
2.) I assume the path has been sniffed, are other records used as well, say
SRV?
3.) Not sure why a particular record would be used to determine availability
as
really any RR could serve for this (including made up ones).
[OK, not phrased in the form of a question]
4.) What problem is being solved here? Generally, with end devices DNS
resolution
starts at the top of its DNS resolver list and tries until it gets an
answer
or critical error (still an answer) within a timeout period. The next
query
takes the same route and so on. There are exceptions in implementation
where
statistics are maintained and its DNS resolver list is reordered
accordingly
but to blacklist and probe seems like a lot of wasted calories.
For example:
* What is the percentage of nameservers it would blacklist before
it determines it is almost out of options?
* Would it completely deny itself DNS service because of a few dropped
packets or localized/ temporary network problems?
* How many packet drops before it blacklists a nameserver?
* How often does it probe for availability (whitelist)?
Without knowing more this seemingly makes for a much more unreliable DNS
experience.
Just curious,
John
>
> Hence my question,
> What Kind of messages are required by the client to be sent towards server to
> determine if the DNS IP is reachable or not?
I believe this may have already been answered but any query will work for
this purpose (including the "ANY" query).
>
> Thanks
> Harshith
>
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