SRV Record Server Availability

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SRV Record Server Availability

Bind-Users forum mailing list
Hi,

Is DNS Bind SRV record can detect the Server's availability? If yes, how?

Thank you,
Wil


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Re: SRV Record Server Availability

Bind-Users forum mailing list
On Tue, Jan 5, 2021 at 4:30 AM Wilfred Sarmiento via bind-users
<[hidden email]> wrote:
> Is DNS Bind SRV record can detect the Server's availability? If yes, how?

Could you provide more information about your goal?  I don't fully
understand the question.

For my reading, the answer is basically no, in that an SRV record just
provides data about where.a particular service can be found.  It's up
to other systems to fetch that data and interpret it, including
whether that service is actually available at the given endpoint.  In
its typical operation, BIND will just take whatever name and port the
zone administrator said to provide for that SRV record, and not do any
sort of availability checks on it.

However, if you go deep into a far more complicated, custom use of
BIND, you could set up a process that monitors the availability and
changes the SRV record accordingly.
--
tale
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Re: SRV Record Server Availability

Bind-Users forum mailing list
Hi Tale, Happy new year! 

Your understanding is correct, i just thought that SRV can detect whose server is alive so it can choose and provide an answer with the available Server.

Thank you! 



On Tue, 5 Jan 2021, 23:53 tale <[hidden email]> wrote:
On Tue, Jan 5, 2021 at 4:30 AM Wilfred Sarmiento via bind-users
<[hidden email]> wrote:
> Is DNS Bind SRV record can detect the Server's availability? If yes, how?

Could you provide more information about your goal?  I don't fully
understand the question.

For my reading, the answer is basically no, in that an SRV record just
provides data about where.a particular service can be found.  It's up
to other systems to fetch that data and interpret it, including
whether that service is actually available at the given endpoint.  In
its typical operation, BIND will just take whatever name and port the
zone administrator said to provide for that SRV record, and not do any
sort of availability checks on it.

However, if you go deep into a far more complicated, custom use of
BIND, you could set up a process that monitors the availability and
changes the SRV record accordingly.
--
tale

This e-mail message (including attachments, if any) is intended for the use of the individual or the entity to whom it is addressed and may contain information that is privileged, proprietary, confidential and exempt from disclosure. If you are not the intended recipient, you are notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender and delete this E-mail message immediately.


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Re: SRV Record Server Availability

Matus UHLAR - fantomas
On 06.01.21 21:41, Wilfred Sarmiento via bind-users wrote:
>Your understanding is correct, i just thought that SRV can detect whose
>server is alive so it can choose and provide an answer with the available
>Server.

DNS is not designed to provide this functionality. While technically you can
change contents of DNS depending on which servers are alive and which are
not, it's almost never a good idea.

That means, BIND has nothing like this built in.

>> On Tue, Jan 5, 2021 at 4:30 AM Wilfred Sarmiento via bind-users
>> <[hidden email]> wrote:
>> > Is DNS Bind SRV record can detect the Server's availability? If yes, how?

>On Tue, 5 Jan 2021, 23:53 tale <[hidden email]> wrote:
>> Could you provide more information about your goal?  I don't fully
>> understand the question.
>>
>> For my reading, the answer is basically no, in that an SRV record just
>> provides data about where.a particular service can be found.  It's up
>> to other systems to fetch that data and interpret it, including
>> whether that service is actually available at the given endpoint.  In
>> its typical operation, BIND will just take whatever name and port the
>> zone administrator said to provide for that SRV record, and not do any
>> sort of availability checks on it.
>>
>> However, if you go deep into a far more complicated, custom use of
>> BIND, you could set up a process that monitors the availability and
>> changes the SRV record accordingly.

--
Matus UHLAR - fantomas, [hidden email] ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
Microsoft dick is soft to do no harm
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Re: SRV Record Server Availability

Andrew P.
Isn't this sort of dynamic functionality (real-time presence or absence of SRV records) what mDNS and the avahi daemon are for?

________________________________________
From: bind-users <[hidden email]> on behalf of Matus UHLAR - fantomas <[hidden email]>
Sent: Wednesday, January 6, 2021 8:51 AM
To: [hidden email]
Subject: Re: SRV Record Server Availability

On 06.01.21 21:41, Wilfred Sarmiento via bind-users wrote:
>Your understanding is correct, i just thought that SRV can detect whose
>server is alive so it can choose and provide an answer with the available
>Server.

DNS is not designed to provide this functionality. While technically you can
change contents of DNS depending on which servers are alive and which are
not, it's almost never a good idea.

That means, BIND has nothing like this built in.

>> On Tue, Jan 5, 2021 at 4:30 AM Wilfred Sarmiento via bind-users
>> <[hidden email]> wrote:
>> > Is DNS Bind SRV record can detect the Server's availability? If yes, how?

>On Tue, 5 Jan 2021, 23:53 tale <[hidden email]> wrote:
>> Could you provide more information about your goal?  I don't fully
>> understand the question.
>>
>> For my reading, the answer is basically no, in that an SRV record just
>> provides data about where.a particular service can be found.  It's up
>> to other systems to fetch that data and interpret it, including
>> whether that service is actually available at the given endpoint.  In
>> its typical operation, BIND will just take whatever name and port the
>> zone administrator said to provide for that SRV record, and not do any
>> sort of availability checks on it.
>>
>> However, if you go deep into a far more complicated, custom use of
>> BIND, you could set up a process that monitors the availability and
>> changes the SRV record accordingly.

--
Matus UHLAR - fantomas, [hidden email] ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
Microsoft dick is soft to do no harm
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Re: SRV Record Server Availability

Mark Andrews
Well mDNS is not DNS.  It is a multicast request to all devices on the local network to respond.

To get the functionality being requested in the DNS it requires something to be polling the availability of the server listed in the SRV records and to add/remove/adjust them depending upon their load/availability.  In reality this should not be needed if people would just write client software to properly handle multi-homed servers.  There is nothing that say you must wait for a connection to timeout before you attempt to connect to a second address.

Happy Eyeballs RFC 8305 (previously RFC 6555) us about starting multiple connections across address families and only proceeding with the first that connects but there is NOTHING that says you can’t do the similar for all addresses independent of address family.

It isn’t hard to write a TCP client that attempts to connect to multiple servers simultaneously.

I will admit that it is slightly harder for UDP clients but in most cases it is not impossible.

For both protocols you do not wait seconds to get the initial response before trying the alternate addresses.  Most of the world is less that 300ms way (round trip).

Mark

> On 7 Jan 2021, at 03:42, Andrew P. <[hidden email]> wrote:
>
> Isn't this sort of dynamic functionality (real-time presence or absence of SRV records) what mDNS and the avahi daemon are for?
>
> ________________________________________
> From: bind-users <[hidden email]> on behalf of Matus UHLAR - fantomas <[hidden email]>
> Sent: Wednesday, January 6, 2021 8:51 AM
> To: [hidden email]
> Subject: Re: SRV Record Server Availability
>
> On 06.01.21 21:41, Wilfred Sarmiento via bind-users wrote:
>> Your understanding is correct, i just thought that SRV can detect whose
>> server is alive so it can choose and provide an answer with the available
>> Server.
>
> DNS is not designed to provide this functionality. While technically you can
> change contents of DNS depending on which servers are alive and which are
> not, it's almost never a good idea.
>
> That means, BIND has nothing like this built in.
>
>>> On Tue, Jan 5, 2021 at 4:30 AM Wilfred Sarmiento via bind-users
>>> <[hidden email]> wrote:
>>>> Is DNS Bind SRV record can detect the Server's availability? If yes, how?
>
>> On Tue, 5 Jan 2021, 23:53 tale <[hidden email]> wrote:
>>> Could you provide more information about your goal?  I don't fully
>>> understand the question.
>>>
>>> For my reading, the answer is basically no, in that an SRV record just
>>> provides data about where.a particular service can be found.  It's up
>>> to other systems to fetch that data and interpret it, including
>>> whether that service is actually available at the given endpoint.  In
>>> its typical operation, BIND will just take whatever name and port the
>>> zone administrator said to provide for that SRV record, and not do any
>>> sort of availability checks on it.
>>>
>>> However, if you go deep into a far more complicated, custom use of
>>> BIND, you could set up a process that monitors the availability and
>>> changes the SRV record accordingly.
>
> --
> Matus UHLAR - fantomas, [hidden email] ; http://www.fantomas.sk/
> Warning: I wish NOT to receive e-mail advertising to this address.
> Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
> Microsoft dick is soft to do no harm
> _______________________________________________
> Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe from this list
>
> ISC funds the development of this software with paid support subscriptions. Contact us at https://www.isc.org/contact/ for more information.
>
>
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>
> ISC funds the development of this software with paid support subscriptions. Contact us at https://www.isc.org/contact/ for more information.
>
>
> bind-users mailing list
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