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

[Charles Goldsmith]

Anthony, it doesn't help that the SRND is also lighter in terms of total
number of pages than it used to be.  Back in the 8.x days, it was over 1400
pages.  With all of the new technology and features added through to
version 12.x, you would expect it to get larger, not smaller.


On Fri, Apr 6, 2018 at 10:31 AM Anthony Holloway <
avholloway+cisco-voip at gmail.com> wrote:

> 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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