<html><head><style type="text/css">.style1 {font-family: "Times New Roman";}</style></head><body>Yorgos:<BR>
<BR>
Thanks for the response. But we do not want to receive an answer with ttl = 0 as the application uses the ttl value to start its own refresh timer. For now I have made the timer value tt1+1 if ttl !=0 and ttl=prev ttl otherwise, so applications goes to unbound 1 sec after expiry.<BR>
<BR>
Ideally we want unbound not to send response with ttl=0, instead do the new fetch and return the answer to new fetch without 1 sec delay. After all the application re-queried unbound only after ttl secs expired. The reason is there is certain certification that requires compliance of ttl value for re-queries.<BR>
<BR>
In essence we do not want unbound to maintain cache at all, as the higher application does that, but I could not find a way to configure unbound to not cache. Setting cache-max-ttl to zero has the undesirable side effect of always returning ttl=0 for any query.<BR>
<BR>
Thanks<BR>
Sankar<BR>
<BR>
On 29/06/23, 5:30 PM, "Unbound-users on behalf of <a href="mailto:unbound-users-request@lists.nlnetlabs.nl">unbound-users-request@lists.nlnetlabs.nl</a> <mailto:unbound-users-request@lists.nlnetlabs.nl>" <unbound-users-bounces@lists.nlnetlabs.nl <mailto:unbound-users-bounces@lists.nlnetlabs.nl> on behalf of <a href="mailto:unbound-users-request@lists.nlnetlabs.nl">unbound-users-request@lists.nlnetlabs.nl</a> <mailto:unbound-users-request@lists.nlnetlabs.nl>> wrote:<BR>
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Today's Topics:<BR>
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<BR>
1. Re: Disable Serving expired with ttl=0<BR>
(George (Yorgos) Thessalonikefs)<BR>
<BR>
<BR>
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----------------------------------------------------------------------<BR>
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<BR>
Message: 1<BR>
Date: Thu, 29 Jun 2023 12:50:02 +0200<BR>
From: "George (Yorgos) Thessalonikefs" <george@nlnetlabs.nl <mailto:george@nlnetlabs.nl>><BR>
To: <a href="mailto:unbound-users@lists.nlnetlabs.nl">unbound-users@lists.nlnetlabs.nl</a> <mailto:unbound-users@lists.nlnetlabs.nl><BR>
Subject: Re: Disable Serving expired with ttl=0<BR>
Message-ID: <c4c2bfcb-8a6e-eb2c-d0e0-95e03ce04593@nlnetlabs.nl <mailto:c4c2bfcb-8a6e-eb2c-d0e0-95e03ce04593@nlnetlabs.nl>><BR>
Content-Type: text/plain; charset=UTF-8; format=flowed<BR>
<BR>
<BR>
Hi Sankar,<BR>
<BR>
<BR>
A TTL of 0 does not mean that the record is expired.<BR>
Unbound returns the non-expired (0 TTL) record and starts prefetching; <BR>
since I see that this is enabled in the configuration.<BR>
<BR>
<BR>
If you query 1 second later when the record is expired, Unbound will go <BR>
to the network instead.<BR>
<BR>
<BR>
Best regards,<BR>
-- Yorgos<BR>
<BR>
<BR>
On 29/06/2023 12:26, Raman, Sankar via Unbound-users wrote:<BR>
> Hello:<BR>
> <BR>
> I am working on replacing libcares with unbound for my client on an <BR>
> OpenWrt platform. I am using async mode ( ub_resolve_async() ) for DNS <BR>
> queries and unbound is used as a forwarding server and not authoritative <BR>
> one. serve-expired is left at default which is 'no..<BR>
> <BR>
> The issue I am facing is the application that uses unbound maintains its <BR>
> own cache and on expiry of ttl re-queries unbound which immediately <BR>
> returns an answer with ttl=0 and then sends a fresh query out. This is <BR>
> not desirable for our application. If the application re-queries after <BR>
> tt+1 second then unbound returns answer from fresh query instead serving <BR>
> expired with ttl=0.<BR>
> <BR>
> 1. Why does unbound return expired record with ttl=0 when serve-expired <BR>
> is left at default which is 'no.<BR>
> <BR>
> 2. Why does unbound always sends out new query only after 1 sec after <BR>
> ttl expiry instead of immediately sending new query?<BR>
> <BR>
> Very First Query<BR>
> <BR>
> Application ---> Query ----------------->?????? Unbound<BR>
> <BR>
> <BR>
> ???????????????????????????? Unbound ---> Query ---> Authoritative DNS <BR>
> Server<BR>
> <BR>
> <BR>
> ??????????????????????????????? Unbound ?<--- Answer (ttl = t) <--- <BR>
> Authoritative DNS Server<BR>
> <BR>
> Application <--- Answer (ttl = t) < ----------Unbound<BR>
> <BR>
> After ttl t secs expiry, Second Query<BR>
> <BR>
> Application ---> Query ----------------->?????? Unbound<BR>
> <BR>
> Application <--- Answer (ttl = 0) < ---------Unbound. (*NOT DESIRABLE*)<BR>
> <BR>
> ??????????????????????????????????????????????????????????????????????????????? Unbound 1 sec wait (*NOT DESIRABLE*)<BR>
> <BR>
> <BR>
> ???????????????????????????? Unbound ---> Query ---> Authoritative DNS <BR>
> Server<BR>
> <BR>
> <BR>
> ??????????????????????????????? Unbound? <--- Answer (ttl = t) <--- <BR>
> Authoritative DNS Server<BR>
> <BR>
> This process of getting back ttl=0 repeats for all subsequent re-queries <BR>
> on ttl expiry and Application gets orig ttl only from answer to very <BR>
> first query.<BR>
> <BR>
> As can be seen from the attached wireshark, the lowest ttl=5 and my <BR>
> application re-queries every 5 seconds but unbound sends query out only <BR>
> after 6 seconds as can be seen in wireshark.<BR>
> <BR>
> Attached unbound.conf.<BR>
> <BR>
> Any help will be appreciated.<BR>
> <BR>
> Thanks<BR>
> <BR>
> Sankar Raman<BR>
> <BR>
> <BR>
> <BR>
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