[cisco-voip] session target dns

Thu Mar 15 12:41:15 EDT 2018

Will the SIP provider remain nameless in this thread?  ;)

On Thu, Mar 15, 2018 at 10:58 AM Ed Leatherman <ealeatherman at gmail.com>
wrote:

> I get the impression that im the first customer on these new sbc's.
>
> On Thu, Mar 15, 2018, 11:12 AM Anthony Holloway <
> avholloway+cisco-voip at gmail.com> wrote:
>
>> Wow.  So you pointed out a flaw in the provider network.  Presumably,
>> they were hosting other customers with the same setup; so how in the world
>> was it working for the others?  Or maybe you are the beta tester?
>>
>> On Thu, Mar 15, 2018 at 9:54 AM Ed Leatherman <ealeatherman at gmail.com>
>> wrote:
>>
>>> Follow-up for posterity..
>>>
>>> I had a feeling this was the case but got some confirmation from TAC:
>>> "This is working as designed when this is an incoming call, the reason
>>> why it works that way is because on the incoming leg the call comes from 1
>>> specific IP address, and if CUBE does a DNS query for SRV it might resolve
>>> a different IP address than the one where INVITE is coming from and might
>>> cause inbound calls to fail. Instead, if CUBE does DNS query for A record
>>> it will resolve one specific IP address."
>>>
>>>
>>> The service provider changed their SBC to send an IP address in the
>>> Contact field URI which resolved the issue.
>>>
>>>
>>> Ed
>>>
>>> On Thu, Mar 8, 2018 at 2:16 PM, Ed Leatherman <ealeatherman at gmail.com>
>>> wrote:
>>>
>>>>
>>>> Follow-up to this SRV/CUBE topic..
>>>>
>>>> Outbound calls work fine with this setup (after I enabled ip
>>>> domain-lookup ;-) )
>>>>
>>>> For inbound calls, the service provider is using the hostname for the
>>>> SRV record (peer.isc.lumos.net) in the contact field of the invite.
>>>> Apparently, CUBE only does an A record lookup on that field?
>>>>
>>>> 022206: Mar  8 13:44:04 est:
>>>> //25051/829EEEDD9B28/SIP/Info/verbose/4608/sipSPIProcessContactInfo:
>>>> Previous Hop peer.isc.lumos.net:5060
>>>> ...
>>>> 022210: Mar  8 13:44:04 est:
>>>> //-1/xxxxxxxxxxxx/SIP/Info/info/8192/sip_dns_type_a_aaaa_query: DNS query
>>>> for peer.isc.lumos.net and type:1
>>>> 022211: Mar  8 13:44:04 est:
>>>> //-1/xxxxxxxxxxxx/SIP/Error/sip_dns_type_a_query:
>>>>  TYPE A query failed for peer.isc.lumos.net
>>>> 022212: Mar  8 13:44:04 est:
>>>> //-1/xxxxxxxxxxxx/SIP/Error/_send_dns_fail:
>>>>  DNS Query for peer.isc.lumos.net failed
>>>>
>>>> CUBE is basically shutting down the call saying it can't resolve the
>>>> contact field. If I put a local host entry for that name using their
>>>> currently active SBC, inbound calls work. Shouldn't CUBE be doing a SRV
>>>> lookup here, or should the service provider send me an hostname instead of
>>>> an SRV in this field?
>>>>
>>>>
>>>>
>>>>
>>>> On Tue, Mar 6, 2018 at 2:25 PM, Anthony Holloway <
>>>> avholloway+cisco-voip at gmail.com> wrote:
>>>>
>>>>> Just so you know, they're not going to know if you use SRV records or
>>>>> not, or host records for that matter.  They probably only care about two
>>>>> things:
>>>>>
>>>>> 1) They control which peers you send traffic to via DNS updates
>>>>>
>>>>> 2) They receive the proper/expected host portion in your traffic to
>>>>> them
>>>>>
>>>>> For all intents and purposes, the inclusion of a name in the host
>>>>> portion of a SIP URI is separate from the DNS query.
>>>>>
>>>>> The fact that you point your system at a name (or IP for that matter)
>>>>> and that it then becomes the RHS of the URI is nice, but not required.
>>>>>
>>>>> Therefore, if you ask them to commit to telling you about IP address
>>>>> changes completely negates their desire to use SRV records.  Just say'n.
>>>>>
>>>>> On Tue, Mar 6, 2018 at 6:30 AM Ed Leatherman <ealeatherman at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Thanks Anthony, That was spot on what I was trying to figure out.
>>>>>> I've been using server-groups up until now (and will continue on the CUCM
>>>>>> facing side), the service provider is forcing the change on the side facing
>>>>>> them.
>>>>>>
>>>>>> Loren: That's an interesting idea to lock in the host resolution on
>>>>>> the CUBE itself, but in this case I think it might set me up for an outage
>>>>>> if the service provider changes their IP Addressing. Maybe I can get them
>>>>>> to commit to telling me before they change those..
>>>>>>
>>>>>> On Mon, Mar 5, 2018 at 2:31 PM, Anthony Holloway <
>>>>>> avholloway+cisco-voip at gmail.com> wrote:
>>>>>>
>>>>>>> Loren,
>>>>>>>
>>>>>>> Just out of curiosity, why didn't you just use session server
>>>>>>> groups?  Based on the config you shared, it looks like it would achieve the
>>>>>>> same thing, but with less config, and not adding in the DNS stack within
>>>>>>> IOS.
>>>>>>>
>>>>>>> Ed,
>>>>>>>
>>>>>>> *Note, you cannot use DNS in server groups, so it's one or the other.
>>>>>>>
>>>>>>> I also think it's important to know that the IOS code is written
>>>>>>> such that it will look for SRV records first, and then fallback to looking
>>>>>>> for an A (host) record once the DNS timeouts.
>>>>>>>
>>>>>>> E.g.,
>>>>>>>
>>>>>>> You enter "session target dns:collab.domain.com"
>>>>>>>
>>>>>>> IOS looks for _sip._udp.collab.domain.com SRV record first,
>>>>>>> timesout, then looks for collab.domain.com host record second.
>>>>>>>
>>>>>>> *Note that the outgoing session transport on IOS is UDP by default,
>>>>>>> unless you change it to TCP with the command "session transport tcp" at the
>>>>>>> "voice service voip" level, or at the dial-peer level.  So, having a
>>>>>>> _sip._tcp SRV record on your CUBE would create a confusing scenario.
>>>>>>> Contrast this with the incoming connection, which can be either.  However,
>>>>>>> SRV records, like Loren is showing, are for outbound connection
>>>>>>> establishments.
>>>>>>>
>>>>>>> I have not done an extensive amount of testing here, but I would be
>>>>>>> curious to know if IOS handles the TTL for the DNS record correctly, or if
>>>>>>> it queries DNS for every setup like how that one defect was hitting CUCM
>>>>>>> SIP trunks for a while there.  I looked for "TTL" in the CVP Config guide,
>>>>>>> but it didn't say.
>>>>>>>
>>>>>>> On Mon, Mar 5, 2018 at 11:19 AM Loren Hillukka <
>>>>>>> lchillukka at hotmail.com> wrote:
>>>>>>>
>>>>>>>> You can have your gw query your DNS server, and you have to add SRV
>>>>>>>> records to your central DNS server (like with the jabber entries required
>>>>>>>> to get jabber sign-in to work).
>>>>>>>>
>>>>>>>> Here’s the example of doing local DNS to static entries on the
>>>>>>>> gateway itself, from the CVP 10 config guide.  CVP is where I first started
>>>>>>>> doing dns srv on the local gateway, as I preferred breaking the call center
>>>>>>>> myself instead of having the AD/DNS teams do it for me without me knowing
>>>>>>>> ;-)
>>>>>>>>
>>>>>>>> ===========
>>>>>>>>
>>>>>>>> You can also configure the Gateway statically instead of using DNS.
>>>>>>>> The following example shows how both the A and SRV type records could be
>>>>>>>> configured:
>>>>>>>>
>>>>>>>> ip host cvp4cc2.cisco.com 10.4.33.132
>>>>>>>>
>>>>>>>> ip host cvp4cc3.cisco.com 10.4.33.133
>>>>>>>>
>>>>>>>> ip host cvp4cc1.cisco.com 10.4.33.131
>>>>>>>>
>>>>>>>> For SIP/TCP:
>>>>>>>>
>>>>>>>> ip host _sip._tcp.cvp.cisco.com srv 50 50 5060 <50%2050%205060>
>>>>>>>> cvp4cc3.cisco.com
>>>>>>>>
>>>>>>>> ip host _sip._tcp.cvp.cisco.com srv 50 50 5060 <50%2050%205060>
>>>>>>>> cvp4cc2.cisco.com
>>>>>>>>
>>>>>>>> ip host _sip._tcp.cvp.cisco.com srv 50 50 5060 <50%2050%205060>
>>>>>>>> cvp4cc1.cisco.com
>>>>>>>>
>>>>>>>> For SIP/UDP:
>>>>>>>>
>>>>>>>> ip host _sip._udp.cvp.cisco.com srv 50 50 5060 <50%2050%205060>
>>>>>>>> cvp4cc3.cisco.com
>>>>>>>>
>>>>>>>> ip host _sip._udp.cvp.cisco.com srv 50 50 5060 <50%2050%205060>
>>>>>>>> cvp4cc2.cisco.com
>>>>>>>>
>>>>>>>> ip host _sip._udp.cvp.cisco.com srv 50 50 5060 <50%2050%205060>
>>>>>>>> cvp4cc1.cisco.com
>>>>>>>>
>>>>>>>>  ============
>>>>>>>>
>>>>>>>> Then your dial-peer would have session target dns:cvp.cisco.com which
>>>>>>>> would point to the SRV record, which would use the weight/priority values
>>>>>>>> to choose the final host, and resolve the selected host to an IP using the
>>>>>>>> normal "ip host name x.x.x.x" entry
>>>>>>>>
>>>>>>>>
>>>>>>>> Loren
>>>>>>>>
>>>>>>>> On Mar 5, 2018, at 10:15 AM, Ed Leatherman <ealeatherman at gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>> Hi everyone,
>>>>>>>>
>>>>>>>> Hopefully a quick question - in a dial-peer on CUBE (16.3.5) how
>>>>>>>> does session target dns: resolve to an IP? I've never used DNS as target
>>>>>>>> before for this.
>>>>>>>>
>>>>>>>> Does CUBE just do a query for the A record by default, or does it
>>>>>>>> do a SRV query by default? I have a SIP provider that wants to start using
>>>>>>>> SRV for their SBC(s) and I'm researching how to setup my end in IOS. If it
>>>>>>>> doesn't query SRV default, where do I toggle that behavior?
>>>>>>>>
>>>>>>>> The command reference just says  "Configures the host device
>>>>>>>> housing the domain name system (DNS) server that resolves the name of the
>>>>>>>> dial peer to receive calls."
>>>>>>>>
>>>>>>>> I've found the knob to tell it what SRV format to use in the sip-ua
>>>>>>>> section.
>>>>>>>>
>>>>>>>> Thanks!
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> Ed Leatherman
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> cisco-voip mailing list
>>>>>>>> cisco-voip at puck.nether.net
>>>>>>>> https://puck.nether.net/mailman/listinfo/cisco-voip
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> cisco-voip mailing list
>>>>>>>> cisco-voip at puck.nether.net
>>>>>>>> https://puck.nether.net/mailman/listinfo/cisco-voip
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Ed Leatherman
>>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Ed Leatherman
>>>>
>>>
>>>
>>>
>>> --
>>> Ed Leatherman
>>> _______________________________________________
>>> cisco-voip mailing list
>>> cisco-voip at puck.nether.net
>>> https://puck.nether.net/mailman/listinfo/cisco-voip
>>>
>>
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