Our ISP says they can't restrict zone transfers

[William Bell]

Hey Chris,

Follow-up:
I finally got our zone transfer issue resolved late last week.  As it turns
out, Time Warner Telecom (TWTC) can't enable zone transfers for a specific
IP range, they have to either "turn it on or turn it off."  So I had them
turn it off entirely (except for the TWTC nameservers, of course).  Now my
security guys and my boss are happy.  :/

Unfortunately, the engineer who made the modifications accidentally disabled
DNS for our primary domain too, which created an intermittent outage of our
main website and other services (VPN, etc).  Naturally, as the DNS caches
timed out, the outage became more widespread.  Nice work.

Once we discovered the impending doom, I called TWTC (I have their direct
number now) and worked with them to get it resolved.  It just so happens
that the person who broke our DNS was the same person I had spoken to before
(see my earlier email quote below).  However, to her credit, she admitted to
the mistake, fixed it instantly, and apologized profusely.  Apparently, TWTC
uses a proprietary tool to manage DNS and she's new, so she's still getting
used to the tool. Because the outage was intermittent and we worked quickly
to resolve it, the damage wasn't too bad.

On the plus side, because of the outage, I think I may have established a
better relationship with the engineers at the new TWTC NOC.
Hopefully.

Thanks again for the advice.
-Bill


On 4/10/08 7:56 PM, "William Bell" <bellwm at gmail.com> wrote:

> 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."
>>> 
>>> 
>>> 
>>