[isalist] Re: OT: DNS and Forwarders
- From: "Thor (Hammer of God)" <thor@xxxxxxxxxxxxxxx>
- To: "isalist@xxxxxxxxxxxxx" <isalist@xxxxxxxxxxxxx>
- Date: Thu, 19 Oct 2006 00:25:37 -0700
http://www.ISAserver.org
-------------------------------------------------------
Even with other clients, the web proxy handles that. So unless you have to
have a linux box be able to telnet out to a host name or something then
you're still covered. Worst case, just make them SNAT clients and allow
them to hit the DMZ DNS server based on IP... Problem solved, same level of
protection, just with noted exceptions as they may occur.
And I've already got reliance on my ISP. I mean, they're my ISP. If I
hosted my own DNS that was published (a scenario I already outlined) and
they had problems, people couldn't reach my DNS servers anyway. So that's
kind of a moot point.
With any of the commercial grade providers here servicing corporate clients
it's a no brainer. But even if you had to publish it yourself, you could
basically arrive at the same thing with perimeter networks or whatever.
Point is, the general configuration has everything to offer, and nothing to
lose other than what you would have already lost for your "special"
circumstances anyway. Better security, better performance, flexible
administration. If you've got to work around "proper" solutions because you
don't have ISP's that are worth a crap, then you're not really addressing
the true problem...
t
On 10/18/06 11:04 PM, "Greg Mulholland" <gmulholland@xxxxxxxxxxxx> spoketh
to all:
> http://www.ISAserver.org
> -------------------------------------------------------
>
> Agree with the not allowing lan boxes udp 53 out and in..
>
> however.. in a mixed environment where you have unix/linux/vms and other non
> ms machines where the FWC is not available it kinda doesn't work. also the
> whole premise is based on a reliance on the ISP, im sure they would
> understand your concerns when your dns namespace resolution is up the spout
> and would be very prompt in fixing your problem. Ive had issues with most of
> the ISP's (at least in AUS) and my decision to rely on them dies as long as
> am here.
>
> .02 , Thanks
>
> Greg
> ----- Original Message -----
> From: "Thor (Hammer of God)" <thor@xxxxxxxxxxxxxxx>
> To: <isalist@xxxxxxxxxxxxx>
> Sent: Thursday, October 19, 2006 1:50 PM
> Subject: [isalist] Re: OT: DNS and Forwarders
>
>
>> http://www.ISAserver.org
>> -------------------------------------------------------
>>
>> I've found that many people seem to dance over the security ramifications
>> of
>> DNS/forwarders when designing an infrastructure. I had some off-list
>> conversations about this, and thought that it may be valuable to fully
>> flesh-out what I think the issues are and how to avoid them. Now's also
>> probably a good time to share my "trick" regarding publicly available DNS
>> and minimizing service exposure. So, for the benefit of those who are
>> interested:
>>
>> When AD DNS is configured as a forwarder, all domain members using that
>> DNS
>> server will be able to resolve hostnames directly from their IP stack.
>> There is no operational reason to have this-- when one considers that most
>> spyware/malware/trojans/backdoors/shells/etc typically depend on hostname
>> lookups for direct access to a resource, the capability of a client box to
>> perform direct host lookups outside your network should (to me) be
>> considered unwanted and un-needed. Personally, I qualify it as
>> "dangerous."
>>
>> That's why I always configure my AD DNS with a root (.) zone- that way,
>> only
>> local zones may be queried by the client's stack. I typically only use
>> web
>> proxy clients for HTTP(S)/FTP where all DNS is proxied by the ISA box. If
>> one needs direct DNS for another application (say DOS FTP) then use the
>> FWC
>> and all DNS will be resolved over the control channel, still being proxied
>> by the ISA server.
>>
>> The ISA server itself will have whatever "public" DNS server configured in
>> its stack so that it can do the resolution for the clients.
>>
>> Not only is direct client DNS "dangerous," but having an AD box set up as
>> a
>> forwarder is "dangerous" as well as the box must be configured to access a
>> remote resource over TCP/UDP 53. This also means that you've opened that
>> box up for incoming traffic on TCP/UDP 53 as well. Having static paths
>> into
>> your internal network from source port routing is crazy. I can push
>> anything I want over 53, not just DNS (and have ;). Remember, the DNS
>> filter is only for published DNS servers, not clients requesting DNS
>> lookups.
>>
>> But there is the issue of one wanting complete control over host names and
>> the need to publish your own DNS. This is what the DMZ is for. The DMZ
>> box
>> is set as a forwarding server, and the internal ISA box is set to use that
>> box for all DNS requests. In this way, only the ISA box itself need to
>> request DNS outside the internal network, and it is already protected. In
>> this manner, there is no DNS leaving the internal network at all, and no
>> static ports into the internal network-- only the ISA box looking up DNS,
>> and only to that DMZ resource. The DNS server in the DMZ is protected by
>> the border ISA box, which (where necessary) is publishing DNS to the DMZ
>> for
>> remote hosts to look up your domain information. And here the DNS filter
>> is
>> used.
>>
>> But you can get even better than that-- you can actually be fully in
>> control
>> of your own zone data without having to actually publish your DNS to the
>> world if you have a decent ISP.
>>
>> Here's what I do for that-- I have DMZ DNS servers set up as primary DNS
>> zones, and have told my ISP to set up their servers as secondary zones for
>> my domains. The DMZ box can only zone transfer to the IP's of my ISP's
>> DNS
>> servers. Additionally the DMZ box is set to forward to my ISP's cache
>> servers. So, at this point, all internal AD DNS is stopped at the
>> controller, and only the ISA box can resolve DNS and only to the DMZ DNS
>> server. My internal Exchange clusters' stack resolves to the AD
>> controller,
>> and they smart host deliver mail to my DMZ GFI gateway, so still no DNS
>> leaving. The GFI box in the DMZ uses the DMZ DNS.
>>
>> The trick is that though I'm primary DNS, and though any changes I make to
>> my DNS hosts are immediately replicated to my ISP as secondary DNS, I've
>> registered my DNS with the domain registry as my *ISP* being primary. So
>> the world resolves my host names via my *ISP's* DNS servers, not *mine*.
>> I
>> don't even have to publish DNS at all.
>>
>> The end result is that no DNS requests leave my internal network at all,
>> except for a single DNS box in the DMZ that can only resolve to the ISP
>> DNS
>> caches. There is no publishing at all, no internal paths, no vulns,
>> nothing
>> at all since the world resolves to the ISP boxes yet I have full control
>> over all host name entries.
>>
>> It's a pretty tight config.
>>
>> t
>>
>>
>>
>> On 10/18/06 11:01 AM, "Thomas W Shinder" <tshinder@xxxxxxxxxxx> spoketh to
>> all:
>>
>>> http://www.ISAserver.org
>>> -------------------------------------------------------
>>>
>>> The T-Man is definitely right about this.
>>>
>>> Thomas W Shinder, M.D.
>>> Site: www.isaserver.org
>>> Blog: http://blogs.isaserver.org/shinder/
>>> Book: http://tinyurl.com/3xqb7
>>> MVP -- Microsoft Firewalls (ISA)
>>>
>>>
>>>
>>>> -----Original Message-----
>>>> From: isalist-bounce@xxxxxxxxxxxxx
>>>> [mailto:isalist-bounce@xxxxxxxxxxxxx] On Behalf Of Thor
>>>> (Hammer of God)
>>>> Sent: Wednesday, October 18, 2006 12:52 PM
>>>> To: isalist@xxxxxxxxxxxxx
>>>> Subject: [isalist] Re: OT: DNS and Forwarders
>>>>
>>>> http://www.ISAserver.org
>>>> -------------------------------------------------------
>>>>
>>>> Why do your internal clients need to resolve DNS directly? I
>>>> never ever use
>>>> forwarders on my AD boxes. I always create root zones on my
>>>> AD DNS servers
>>>> and only use ISA to resolve DNS for web proxy/fw clients.
>>>>
>>>> That's where what I consider "true" security and separation
>>>> comes from.
>>>>
>>>> t
>>>>
>>>>
>>>> On 10/18/06 9:13 AM, "ISA" <ISA@xxxxxxxxxxxxxxxx> spoketh to all:
>>>>
>>>>> http://www.ISAserver.org
>>>>> -------------------------------------------------------
>>>>>
>>>>>
>>>>> This actually has happened with and without forwarders -
>>>>>
>>>>> Steve, I interpret your suggestion as using only the Root Hints?
>>>>>
>>>>>
>>>>>
>>>>> Joseph Danielsen, MCSA-Messaging, MCP
>>>>>
>>>>> Network Blade Inc.
>>>>>
>>>>> 49 Marcy Street
>>>>>
>>>>> Somerset, NJ 08873
>>>>>
>>>>> 732-213-0600
>>>>>
>>>>> www.networkblade.com
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: isalist-bounce@xxxxxxxxxxxxx
>>>> [mailto:isalist-bounce@xxxxxxxxxxxxx]
>>>>> On Behalf Of Steve Moffat
>>>>> Posted At: Wednesday, October 18, 2006 12:08 PM
>>>>> Posted To: ISA
>>>>> Conversation: [isalist] Re: OT: DNS and Forwarders
>>>>> Subject: [isalist] Re: OT: DNS and Forwarders
>>>>>
>>>>> http://www.ISAserver.org
>>>>> -------------------------------------------------------
>>>>>
>>>>> FWIW.....I have 2 caching only DNS Servers that I setup to use as
>>>>> forwarders for my AD DNS Servers, when I use them, I get
>>>> the very same
>>>>> issue. If I however, remove them from the forwarders
>>>> section, I have no
>>>>> DNS Issues at all whatsoever, anytime.
>>>>>
>>>>> S
>>>>>
>>>>> -----Original Message-----
>>>>> From: isalist-bounce@xxxxxxxxxxxxx
>>>> [mailto:isalist-bounce@xxxxxxxxxxxxx]
>>>>> On Behalf Of ISA
>>>>> Sent: Wednesday, October 18, 2006 1:03 PM
>>>>> To: ISA Mailing List
>>>>> Subject: [isalist] Re: OT: DNS and Forwarders
>>>>>
>>>>> http://www.ISAserver.org
>>>>> -------------------------------------------------------
>>>>>
>>>>> Thanks Mike:
>>>>>
>>>>> I will try clearing the cache - but this happens now about everyday
>>>>> (morning usually). I really have to find the source of the problem.
>>>>>
>>>>>
>>>>>
>>>>> Joseph Danielsen, MCSA-Messaging, MCP
>>>>>
>>>>> Network Blade Inc.
>>>>>
>>>>> 49 Marcy Street
>>>>>
>>>>> Somerset, NJ 08873
>>>>>
>>>>> 732-213-0600
>>>>>
>>>>> www.networkblade.com
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: isalist-bounce@xxxxxxxxxxxxx
>>>> [mailto:isalist-bounce@xxxxxxxxxxxxx]
>>>>> On Behalf Of Michael Ross
>>>>> Posted At: Wednesday, October 18, 2006 12:01 PM
>>>>> Posted To: ISA
>>>>> Conversation: [isalist] OT: DNS and Forwarders
>>>>> Subject: [isalist] Re: OT: DNS and Forwarders
>>>>>
>>>>> http://www.ISAserver.org
>>>>> -------------------------------------------------------
>>>>>
>>>>> Windows 2003 DNS servers?
>>>>> Believe it or not, ive seen that . It's a cache pollution type of
>>>>> behavior, with no logging or other signs to prove that.
>>>>> Try to clear the DNS cache next time and see if it helps.
>>>>>
>>>>> -----Original Message-----
>>>>> From: isalist-bounce@xxxxxxxxxxxxx
>>>> [mailto:isalist-bounce@xxxxxxxxxxxxx]
>>>>> On Behalf Of ISA
>>>>> Sent: Wednesday, October 18, 2006 10:59 AM
>>>>> To: isalist@xxxxxxxxxxxxx
>>>>> Subject: [isalist] OT: DNS and Forwarders
>>>>>
>>>>> http://www.ISAserver.org
>>>>> -------------------------------------------------------
>>>>>
>>>>> Steve: Funny you should say that because I've done that a few times.
>>>>>
>>>>> DNS stops - I removed the forwards - Restart DNS - DNS works.
>>>>> DNS stops - I change the forwards - Restart DNS - DNS works.
>>>>>
>>>>> I want to blame my server but I'm just not sure where the
>>>> failure is.
>>>>>
>>>>>
>>>>>
>>>>> Joseph Danielsen, MCSA-Messaging, MCP
>>>>>
>>>>> Network Blade Inc.
>>>>>
>>>>> 49 Marcy Street
>>>>>
>>>>> Somerset, NJ 08873
>>>>>
>>>>> 732-213-0600
>>>>>
>>>>> www.networkblade.com
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: isalist-bounce@xxxxxxxxxxxxx
>>>> [mailto:isalist-bounce@xxxxxxxxxxxxx]
>>>>> On Behalf Of Steve Moffat
>>>>> Posted At: Wednesday, October 18, 2006 11:55 AM Posted To: ISA
>>>>> Conversation: [isalist] OT: DNS and Forwarders
>>>>> Subject: [isalist] Re: OT: DNS and Forwarders
>>>>>
>>>>> http://www.ISAserver.org
>>>>> -------------------------------------------------------
>>>>>
>>>>> Remove the forwarders.....then see how fast your Internet speed
>>>>> gets...:)
>>>>>
>>>>> S
>>>>>
>>>>> -----Original Message-----
>>>>> From: isalist-bounce@xxxxxxxxxxxxx
>>>> [mailto:isalist-bounce@xxxxxxxxxxxxx]
>>>>> On Behalf Of ISA
>>>>> Sent: Wednesday, October 18, 2006 12:49 PM
>>>>> To: ISA Mailing List
>>>>> Subject: [isalist] OT: DNS and Forwarders
>>>>>
>>>>> http://www.ISAserver.org
>>>>> -------------------------------------------------------
>>>>>
>>>>> Hello All -
>>>>>
>>>>> This might be off-topic, but has anyone every had their
>>>> Windows DNS/DC
>>>>> server intermittently stop forwarding DNS requests?
>>>>>
>>>>> I checked with the ISP and they don't recognize and
>>>> problems on their
>>>>> end.
>>>>>
>>>>> JD
>>>>> ------------------------------------------------------
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