[cisco-voip] Looking for insight into how Cisco 8851 deals with DNS TTL

[Anthony Holloway]

I'm a little surprised that the spec for DNS support is not well
documented.  It should be in the SRND.  Especially since DNS + Certificates
are more common place today.

On Fri, Apr 6, 2018 at 9:03 AM Wes Sisk (wsisk) <wsisk at cisco.com> wrote:

> Looks like it was known broken at one point:
>
> The DNS Query Response TTL of the secondary DNS server is not being
> respected by the 9971/9951/8831 phones if the primary server goes down
> after the first request.
> Resolution Summary
> CSCut29536 for 8831 IP Phones
> CSCut29519 for 99xx IP Phones
> CSCut75647 for 8811/51 IP phones
>
> So versions and deeper dive required.
>
> -Wes
>
>
> On Apr 5, 2018, at 3:14 PM, Russell Goings <russgoings at rgoings.com> wrote:
>
> Hi all
>    I have a client who was doing some network mucking around and part of
> that maintenance caused the two DNS servers used by a group of IP phones to
> go unavailable.  Some of these phones went unregistered with a reason code
> 13 - TCP KeepAlive Timeout.
>
> What I (OK not me.  Just the client.  Well maybe I am interested as well)
> would like to know is how do the Cisco SIP phones, particularly the 8851
> model, deal with the TTL from the DNS response.
>
> Does the phone honor the DNS TTL and cache the response for 24 hours?
>
> Does the phone have a different cache time for the DNS response?
>
> Does it make a new DNS query every time it sends a keep-alive?
>
> I have never looked into this before and on this Thursday afternoon my
> Google-fu is weak.
>
> And the incident was over a week ago so not much from the phone logs to
> help.
>
> Thanks
>
> Russell Goings (AM)
> IPT Engineer – Dimension Data
> Direct Line 571-203-4021 <(571)%20203-4021>
> russell.goings at dimensiondata.com
> Monday – Friday 8:00 – 5:00 EST
>
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