Our ISP says they can't restrict zone transfers

William Bell bellwm at gmail.com
Thu Apr 10 23:56:41 UTC 2008


Hi Chris,
Thanks for the feedback.  It's very helpful.

Yeah, I tried to find out if there was some sort of restriction that may
have prevented her from doing the allow-transfer statement, but she started
asking me questions that made little sense to me and didn't seem pertinent,
so I just bailed.

We've had TWTC as our DNS host for about 6 years, and, for the most part,
they've been good, but I used to send them the zone file changes verbatim
(in plain text) so they couldn't screw it up.  They may have made 2-3
mistakes total in 6 years, but they were minor (forgot the trailing dot,
etc).  That's why all the crap she was throwing at me caught me by surprise.
It was strange.

You're probably right, they may not be able to "hand edit" the zone files
and their management tool may not allow them to restrict AXFR's per domain.

Anyway, thanks for restoring my confidence in my memory.  I don't have
Alzheimer's yet!  Or do I?  I can't remember.  ;)

If you want, I'll post a follow-up after I call them again tomorrow.
Take care!
Bill


On 4/10/08 7:30 PM, "Chris Buxton" <cbuxton at menandmice.com> wrote:

> An AXFR is a type of zone transfer. The other type is called IXFR, or
> incremental zone transfer.
> 
> Either way, what the TW script monkey told you was completely false,
> as you were already thinking. Restricting zone transfers would not
> stop anyone from retrieving specific records from your zone - that
> statement is called "allow-query", not "allow-transfer".
> 
> It may be that the following are true, thus making it inconvenient for
> TW to restrict zone transfers:
> 
> - They are not using TSIG.
> - The list of source addresses of legitimate zone transfers is not
> well known.
> 
> Or it may simply be that their DNS management tool does not expose
> this functionality.
> 
> I have heard several negative anecdotes about TW's DNS staff. Good
> luck with this.
> 
> Chris Buxton
> Professional Services
> Men & Mice
> 
> On Apr 10, 2008, at 4:08 PM, William Bell wrote:
>> Hi,
>> First, it¹s been a few years since I maintained BIND servers, so
>> please
>> forgive my rustiness.  :)
>> I couldn¹t¹ find an answer to this particular question in the
>> archives, soŠ
>> What valid reason would any ISP or DNS hosting company have for NOT
>> restricting zone transfers to valid nameservers, IP¹s, hosts, etc?
>> 
>> Also, a ³zone transfer² and an AXFR request are the same thing
>> aren¹t they?
>> 
>> Why I¹m asking this question:
>> We recently determined that our ISP/DNS host  (Time Warner Telecom)
>> allows
>> zone transfers for our domains from anywhere on the internet (as far
>> as we
>> can tell).  So I called and asked them to restrict zone transfers
>> for our
>> domains to their own DNS servers and to our internet IP blocks.
>> Sounds like
>> a simple ³allow-transfer² directive in our zone file, right?  Not
>> according
>> to the TW rep I spoke to.  They told me that, since they were the
>> authoritative DNS servers for our domains, if they restricted zone
>> transfers
>> as I requested, then no one would be able to access our DNS and thus
>> no one
>> would be able to access our servers from the internet.  Okay, it¹s
>> been 4 or
>> 5 years since I¹ve done any DNS work, but this response struck me as
>> a bit
>> strange.  I began to suspect that either I was much less informed
>> about DNS
>> than this Time Warner rep or vice versa.
>> 
>> In addition, during the course of the conversation, she also stated
>> with
>> conviction that zone transfers and AXFR¹s were 2 different things.
>> I was so
>> dumbfounded that I that I didn¹t know what to say.  Again, I gave
>> her the
>> benefit of the doubt; I considered that maybe I had been somehow
>> misinformed
>> all these years or that the DNS paradigm had changed ‹ after all
>> this was a
>> ³level 2² person in the DNS group at Time Warner ‹ so I let it go.
>> I just
>> thanked her for her time, asked her to keep the ticket open and told
>> her I
>> would get back to them.
>> 
>> I should¹ve just escalated, but I started this call believing that I
>> was
>> making a simple request; I wasn¹t prepared for a battle.  So I quickly
>> decided that my best tactic was to retreat, regroup, and attack with
>> more
>> troops from a different direction.  Hence this email.  Besides, I
>> wasn¹t
>> sure that I wanted someone who didn¹t quite grasp these concepts
>> making
>> changes to our zone files.
>> 
>> I realize that restricting zone transfers is a minor security
>> enhancement,
>> but every little bit helps.  Besides, my boss told me to get it
>> done.  ;)
>> 
>> Any advice would be greatly appreciated.
>> Thanks
>> 
>> -- 
>> Regards,
>> Bill
>> 
>> "No trees were killed in the making of this e-mail... however,
>> a large number of electrons were terribly inconvenienced."
>> 
>> 
>> 
> 

-- 
Regards,
Bill

"No trees were killed in the making of this e-mail... however,
a large number of electrons were terribly inconvenienced."




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