Re: [dnssd] SRP Update - removing individual services (draft-ietf-dnssd-srp-06)

[Kangping Dong <[e-mail]>]

Sounds good, thanks! Looking forward to the 07 draft!

BRs,
Kangping

On Fri, Dec 18, 2020 at 9:20 PM Ted Lemon <[e-mail]> wrote:

> On Dec 17, 2020, at 11:02 PM, Kangping Dong <[e-mail]> wrote:
>
> I'd like to summary my understanding of what current SRP-draft-06 is
> doing/allowing:
>
>    1. We can add services separately. like, we can add "service-1" and in
>    the first SRP update and "service-2" in the second SRP update.
>    2. We can only remove all the services together with its host because
>    "exactly one Host Description Instruction" is a MUST for each SRP update.
>
> But the spec seems, is not enforcing this behavior:
>
>> Therefore, SRP servers MAY remove all
>> service instances pointing to a host when a host is removed, even if
>> the SRP client doesn't remove them explicitly.
>>
>> If we cannot remove individual service without removing the host, should
> the "MAY" be a MUST?
> Otherwise, there may be no efficient way to clean up the service until the
> lease time expires.
>
>
> Yes, I think this is an oversight in the specification. What my
> implementation actually does is to remove all the entries when we see a
> “lease 0” update with a valid host record that’s signed with the right key.
>
> To remove a service registration, the SRP client retransmits its most
>> recent update with an Update Lease option that has a LEASE value of
>> zero.
>>
>> Does it remove only the services in my most recent update or all services
> I have ever registered?
>
>
> My implementation does the latter. It tracks what services are registered
> per host.
>
> This is what
> I was confused about and thought we can remove individual service. As we
> cannot remove individual service,
> I think we don't need to retransmit the most recent update: It may be more
> efficient to always transmit a
> SRP update with only Host Description Instruction and zero lease time.
> Thoughts?
>
>
> Yes.
>
> For the current use model, I agree it will work for most cases and
> removing individual service may be rare
> (even there are, it can be done with a "removing all" and an add). So I
> don't have a strong opinion to support it.
>
>
> I don’t think we really have enough data to say. In the interests of being
> general, I think it’s probably worth specifying how to remove individual
> services. This is what I’d originally intended—I did the “lease time 0”
> hack because it was expedient, not because it was the right thing to do.
>
> I’ll spin a -07 later today if I have time that makes this change and
> addresses your other concerns from above, and then if you’re willing, you
> guys can review my changes and see if they are sufficient.
>
>