RE: DNS Flag Day: I had to open the TCP/53 port

[Stephan Lagerholm]

Hi Roberto,

You are correct in that the DNS Flag day tester at https://dnsflagday.net/
is reporting the closed TCP port as a serious problem. Given that the TCP
port is closed, obviously the EDNS test over TCP fails too and the error
given by the site would be something like: edns512tcp=timeout

To be RFC compliant you should have both UDP and TCP. Timeouts over UDP
can happen due to natural causes and it is good to give a resolver the
opportunity to fallback to TCP if needed even if you never expect your
server to respond with the Truncate bit set. But I would say the flag day
site is a little bit misleading since the question if TCP should be open
or not is somewhat of an orthogonal problem to EDNS compliance.

Hope this helps explaining the error you are seeing.

Stephan






On Mon, 4 Feb 2019, Salih CIRGAN wrote:

> rfc6891 states that it uses TCP to avoid truncated UDP responses. It is all 
> about packet size,fragmentation and network load.
>
>
>
> EDNS(0) specifies a way to advertise additional features such as
>
>larger response size capability, which is intended to help avoid
>
>truncated UDP responses, which in turn cause retry over TCP.  It
>
>therefore provides support for transporting these larger packet sizes
>
>without needing to resort to TCP for transport.
>
>
>
> Announcing UDP buffer sizes that are too small may result in fallback
>
>to TCP with a corresponding load impact on DNS servers.  This is
>
>especially important with DNSSEC, where answers are much larger.
>
>
>
>
>
>
>
>
>
> From: bind-users [mailto:bind-users-boun...@lists.isc.org] On Behalf Of 
> Roberto Carna
> Sent: Monday, February 4, 2019 4:46 PM
> To: ML BIND Users 
> Subject: DNS Flag Day: I had to open the TCP/53 port
>
>
>
> Dear, I have a BIND 9.10 public server and I have delegated some public 
> domains.
>
>
>
> When I test these domains with the EDNS tool offered in the DNS Flag Day 
> webpage, the test was wrong wit just UDP/53 port opened to Internet.
>
>
>
> After that, when I opened also TCP/53 port, the test was succesful.
>
>
>
> Please can you explain me the reason I have to open TCP/53 port to Internet 
> from February 1st to the future???
>
>
>
> Really thanks, regards.
>
>

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RE: DNS Flag Day: I had to open the TCP/53 port

[Salih CIRGAN]

rfc6891 states that it uses TCP to avoid truncated UDP responses. It is all 
about packet size,fragmentation and network load.

 

EDNS(0) specifies a way to advertise additional features such as

   larger response size capability, which is intended to help avoid

   truncated UDP responses, which in turn cause retry over TCP.  It

   therefore provides support for transporting these larger packet sizes

   without needing to resort to TCP for transport.

 

Announcing UDP buffer sizes that are too small may result in fallback

   to TCP with a corresponding load impact on DNS servers.  This is

   especially important with DNSSEC, where answers are much larger.

 

 

 

 

From: bind-users [mailto:bind-users-boun...@lists.isc.org] On Behalf Of Roberto 
Carna
Sent: Monday, February 4, 2019 4:46 PM
To: ML BIND Users 
Subject: DNS Flag Day: I had to open the TCP/53 port

 

Dear, I have a BIND 9.10 public server and I have delegated some public domains.

 

When I test these domains with the EDNS tool offered in the DNS Flag Day 
webpage, the test was wrong wit just UDP/53 port opened to Internet.

 

After that, when I opened also TCP/53 port, the test was succesful.

 

Please can you explain me the reason I have to open TCP/53 port to Internet 
from February 1st to the future???

 

Really thanks, regards.

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Re: DNS Flag Day: I had to open the TCP/53 port

[Jeronimo L. Cabral]

Ben, thanks a lot !!!

Regards

On Mon, Feb 4, 2019 at 11:04 AM Ben Croswell  wrote:

> When a DNS response is too large to fit in a single UDP packet, 512 bytes
> up to 4k with edns, the DNS server will respond with as much as it can fit
> in the UDP packet. It will also set the truncate, TC, bit to let the client
> doing the query that the answer is truncated and the client should query
> again over TCP for the full answer.
>
> The TC bit is also used in conjunction with RRL.
>
> On Mon, Feb 4, 2019, 8:57 AM Roberto Carna  wrote:
>
>> Thanks Ben for your response, can you tell me the types of TCP traffic I
>> have to expect in BIND, excepting Zone Tansfer?
>>
>> Thans a lot again!!!
>>
>> El lun., 4 feb. 2019 a las 10:50, Ben Croswell ()
>> escribió:
>>
>>> BIND has always required UDP and TCP 53 for proper functionality. It
>>> sometimes mistakenly believed that TCP is only for zone transfers but that
>>> is not the case.
>>>
>>> On Mon, Feb 4, 2019, 8:46 AM Roberto Carna >> wrote:
>>>
 Dear, I have a BIND 9.10 public server and I have delegated some public
 domains.

 When I test these domains with the EDNS tool offered in the DNS Flag
 Day webpage, the test was wrong wit just UDP/53 port opened to Internet.

 After that, when I opened also TCP/53 port, the test was succesful.

 Please can you explain me the reason I have to open TCP/53 port to
 Internet from February 1st to the future???

 Really thanks, regards.
 ___
 Please visit https://lists.isc.org/mailman/listinfo/bind-users to
 unsubscribe from this list

 bind-users mailing list
 bind-users@lists.isc.org
 https://lists.isc.org/mailman/listinfo/bind-users

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Re: DNS Flag Day: I had to open the TCP/53 port

[Ben Croswell]

When a DNS response is too large to fit in a single UDP packet, 512 bytes
up to 4k with edns, the DNS server will respond with as much as it can fit
in the UDP packet. It will also set the truncate, TC, bit to let the client
doing the query that the answer is truncated and the client should query
again over TCP for the full answer.

The TC bit is also used in conjunction with RRL.

On Mon, Feb 4, 2019, 8:57 AM Roberto Carna  Thanks Ben for your response, can you tell me the types of TCP traffic I
> have to expect in BIND, excepting Zone Tansfer?
>
> Thans a lot again!!!
>
> El lun., 4 feb. 2019 a las 10:50, Ben Croswell ()
> escribió:
>
>> BIND has always required UDP and TCP 53 for proper functionality. It
>> sometimes mistakenly believed that TCP is only for zone transfers but that
>> is not the case.
>>
>> On Mon, Feb 4, 2019, 8:46 AM Roberto Carna > wrote:
>>
>>> Dear, I have a BIND 9.10 public server and I have delegated some public
>>> domains.
>>>
>>> When I test these domains with the EDNS tool offered in the DNS Flag Day
>>> webpage, the test was wrong wit just UDP/53 port opened to Internet.
>>>
>>> After that, when I opened also TCP/53 port, the test was succesful.
>>>
>>> Please can you explain me the reason I have to open TCP/53 port to
>>> Internet from February 1st to the future???
>>>
>>> Really thanks, regards.
>>> ___
>>> Please visit https://lists.isc.org/mailman/listinfo/bind-users to
>>> unsubscribe from this list
>>>
>>> bind-users mailing list
>>> bind-users@lists.isc.org
>>> https://lists.isc.org/mailman/listinfo/bind-users
>>>
>> ___
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Re: DNS Flag Day: I had to open the TCP/53 port

[Ron Hall]

Just about anything (if it is large enough).


r

On 2019-02-04 08:56 AM, Roberto Carna wrote:
Thanks Ben for your response, can you tell me the types of TCP traffic I have 
to expect in BIND, excepting Zone Tansfer?

Thans a lot again!!!

El lun., 4 feb. 2019 a las 10:50, Ben Croswell 
(mailto:ben.crosw...@gmail.com>>) escribió:
BIND has always required UDP and TCP 53 for proper functionality. It sometimes 
mistakenly believed that TCP is only for zone transfers but that is not the 
case.

On Mon, Feb 4, 2019, 8:46 AM Roberto Carna 
mailto:robertocarn...@gmail.com> wrote:
Dear, I have a BIND 9.10 public server and I have delegated some public domains.

When I test these domains with the EDNS tool offered in the DNS Flag Day 
webpage, the test was wrong wit just UDP/53 port opened to Internet.

After that, when I opened also TCP/53 port, the test was succesful.

Please can you explain me the reason I have to open TCP/53 port to Internet 
from February 1st to the future???

Really thanks, regards.
___
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--

Ron Hall
Senior System Administrator, NCS - Core Infrastructure Applications
IT Services
T: +1 514 398 3718
ron.h...@mcgill.ca | 
www.mcgill.ca/it

[cid:part7.AFA911F1.FD188252@mcgill.ca]
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Re: DNS Flag Day: I had to open the TCP/53 port

[Roberto Carna]

Thanks Ben for your response, can you tell me the types of TCP traffic I
have to expect in BIND, excepting Zone Tansfer?

Thans a lot again!!!

El lun., 4 feb. 2019 a las 10:50, Ben Croswell ()
escribió:

> BIND has always required UDP and TCP 53 for proper functionality. It
> sometimes mistakenly believed that TCP is only for zone transfers but that
> is not the case.
>
> On Mon, Feb 4, 2019, 8:46 AM Roberto Carna  wrote:
>
>> Dear, I have a BIND 9.10 public server and I have delegated some public
>> domains.
>>
>> When I test these domains with the EDNS tool offered in the DNS Flag Day
>> webpage, the test was wrong wit just UDP/53 port opened to Internet.
>>
>> After that, when I opened also TCP/53 port, the test was succesful.
>>
>> Please can you explain me the reason I have to open TCP/53 port to
>> Internet from February 1st to the future???
>>
>> Really thanks, regards.
>> ___
>> Please visit https://lists.isc.org/mailman/listinfo/bind-users to
>> unsubscribe from this list
>>
>> bind-users mailing list
>> bind-users@lists.isc.org
>> https://lists.isc.org/mailman/listinfo/bind-users
>>
>
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Re: DNS Flag Day: I had to open the TCP/53 port

[Ben Croswell]

BIND has always required UDP and TCP 53 for proper functionality. It
sometimes mistakenly believed that TCP is only for zone transfers but that
is not the case.

On Mon, Feb 4, 2019, 8:46 AM Roberto Carna  Dear, I have a BIND 9.10 public server and I have delegated some public
> domains.
>
> When I test these domains with the EDNS tool offered in the DNS Flag Day
> webpage, the test was wrong wit just UDP/53 port opened to Internet.
>
> After that, when I opened also TCP/53 port, the test was succesful.
>
> Please can you explain me the reason I have to open TCP/53 port to
> Internet from February 1st to the future???
>
> Really thanks, regards.
> ___
> Please visit https://lists.isc.org/mailman/listinfo/bind-users to
> unsubscribe from this list
>
> bind-users mailing list
> bind-users@lists.isc.org
> https://lists.isc.org/mailman/listinfo/bind-users
>
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DNS Flag Day: I had to open the TCP/53 port

[Roberto Carna]

Dear, I have a BIND 9.10 public server and I have delegated some public
domains.

When I test these domains with the EDNS tool offered in the DNS Flag Day
webpage, the test was wrong wit just UDP/53 port opened to Internet.

After that, when I opened also TCP/53 port, the test was succesful.

Please can you explain me the reason I have to open TCP/53 port to Internet
from February 1st to the future???

Really thanks, regards.
___
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