isc domain lookup

Yossi Eskenazi yossi.eskenazi at
Fri May 16 04:38:31 UTC 2014


Thanks for your help. I did a research after asking the question, and
came to the same conclusion. But it didn't occur to me that it could
be a firewall, I thought it was the name server doing it, maybe
blacklisting the domains beginning with "isc". Does the fact that the
query times out show it is a firewall? If it was the dns server, would
it reject the query?

My problem is, I host a domain beginning with "isc", and it cannot get
mail from many domains. If it wasj just "someone", I wouldn't mind,
but there are many domains which cannot get through. The problem
appeared rather recently, so I suspect that an update in a firewall
brand, or a dns server update is causing this.

Thanks for your help.

On Thu, May 15, 2014 at 2:16 AM, Mark Andrews <marka at> wrote:
> Someone trying to block queries in a firewall to prevent
> their servers being used in a amplification attack and causing
> collateral damage through a badly designed rule.
> Mark
> In message <CAPLzrxrary1OtFBFmfL7Svny-AiC7hXPW9c3xRU11U4oYhzOwA at>, Yossi Eskenazi writes:
>> Hello,
>> My question is not directly related to bind, but since it's related to isc
>> I decided to ask here.
>> Some name servers I perform a lookup does not respond to queries, if they
>> begin with "isc"
>> Example server :
>> Query for any domain, it responds. Sometimes it times out, but ask again ,
>> it eventually responds.
>> Query for "" "" "" or just "isc",  it times
>> out.
>> Example server:
>> Query for any domain, it says "query refused"
>> Query for "" "" "" or just "isc",  it times
>> out.
>> It's not just these two, there are other name servers behaving this way.
>> What can be the reason for this?
>> Thanks for your help
>> Y.E.
> --
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                 INTERNET: marka at

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