Re: [dnssd] SRP: Name Conflicts Handling

Kangping Dong <wgtdkp@google.com> Tue, 26 January 2021 03:23 UTC

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From: Kangping Dong <wgtdkp@google.com>
Date: Tue, 26 Jan 2021 11:22:22 +0800
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To: Ted Lemon <mellon@fugue.com>
Cc: DNSSD <dnssd@ietf.org>, Jonathan Hui <jonhui@google.com>, Abtin Keshavarzian <abtink@google.com>, Yakun Xu <xyk@google.com>, Rongli Sun <rongli@google.com>, Simon Lin <simonlin@google.com>
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Subject: Re: [dnssd] SRP: Name Conflicts Handling
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Makes sense, Thanks!

On Sun, Jan 24, 2021 at 11:58 PM Ted Lemon <mellon@fugue.com> wrote:

> If there is a name conflict, it’s because the name is in use. This will
> never happen if the srp server is an authoritative name server: in this
> case there is only one source of truth.
>
> It will only happen if the underlying service is an unauthenticated
> distributed service like mDNS. So in this case we rely on the definition of
> that service to say what will be done. I believe this is discussed in rfc
> 6762 for mDNS.
>
> On Jan 24, 2021, at 01:05, Kangping Dong <wgtdkp@google.com> wrote:
>
> 
> okay, the workflow almost works for me, just a small question. For case 2,
> when the Advertising Proxy detects a name conflict on the multicast link,
> it choses a new name and informs the SRP server the new name. Before the
> client refreshes its service registration, how should the SRP server/Border
> Router
> respond to a DNS query for the original name? I think the BR will reject
> the query with some error like *RESOURCE_NOT_FOUND* / *NAME_NOT_FOUND*,
> as the
> service has already been renamed but just the client hasn't
> been notified yet. right?
>
> On Fri, Jan 22, 2021 at 10:52 PM Ted Lemon <mellon@fugue.com> wrote:
>
>> I think that’s a good description of the solution, yes.
>>
>> On Jan 22, 2021, at 1:02 AM, Kangping Dong <wgtdkp@google.com> wrote:
>>
>> To make sure if I correctly understand how this works, let me explain how
>> a SRP client will handle name conflicts:
>> 1. If a name has already been registered on the SRP server or a name
>> conflict error is returned by the Advertising Proxy:
>>     the SRP server responds with the RR that includes the conflicted
>> name. If the client sees such records, it knows the conflicts
>>    on the SRP server and will retry with a new name.
>> 2. If a name conflict is reported to the SRP server after the SRP update
>> transaction has been committed:
>>     The next time the SRP client registers, the SRP server responds
>> with a CNAME record which includes the new name.
>>     If the client sees such records, it knows the conflict on the
>> multicast link and will accept the name or retry with another name.
>>
>> Am I correct about the workflow?
>>
>>
>> On Fri, Jan 22, 2021 at 12:11 AM Ted Lemon <mellon@fugue.com> wrote:
>>
>>> On Jan 21, 2021, at 12:27 AM, Kangping Dong <wgtdkp@google.com> wrote:
>>>
>>> Option (1) also looks good to me. But what are the RRs that should be
>>> included in the response? SRV RR for service instance name and AAAA/A RR
>>> for host name?
>>>
>>>
>>> Yes, I think that makes sense. These unambiguously indicate what type of
>>> update failed. Which brings up the question of what RRtype to use for
>>> renaming. CNAME?
>>>
>>>
>>