[cisco-voip] SIP Domain substitution

[Ryan Huff]

Hey Nate ... the original ask I think, was to do it all with DNS only and no intervention at layer 4, which to my knowledge, DNS alone couldn’t do.

Expressway search rule, CUCM LUA script... etc could all do it in reality.

However, the actual goal appears to be dialing a Webex cloud registered codec, using a non cloud uri (... at rooms.webex.com), and for that Webex Hybrid calling with Expressway B2B would get you there, and also checks the “no additional transformation needed” box.

Sent from my iPhone

On Oct 4, 2019, at 22:41, NateCCIE <nateccie at gmail.com> wrote:

 I am not thinking right?  Can’t a dns srv get the call routed to a specific host? Then a quick expressway transform to change the domain, and you’re done.

Think of it as a different internal domain va external domain.

Foo at company.com does goes to expressway.companyinfrastructuredomain.com which does a quick trans to foo at internal.local


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On Oct 4, 2019, at 8:36 PM, Lelio Fulgenzi <lelio at uoguelph.ca> wrote:



Interesting. I’ll have to look into that.  Thx.

-sent from mobile device-

Lelio Fulgenzi, B.A. | Senior Analyst
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On Oct 4, 2019, at 10:32 PM, Ryan Huff <ryanhuff at outlook.com<mailto:ryanhuff at outlook.com>> wrote:

Webex Hybrid Calling (with Expressway B2B), could in theory, help accomplish this. The codec is still cloud registered, though Hybrid calling would allow for an on-prem URI to be associated with the Webex remote destination of the codec.

The call would come into the on-prem URI via B2B like normal, and assuming the Hybrid integration was setup correctly, ring the Webex remote destination which rings the cloud registered codec.

It’s a little bit of an ugly trombone, but it does work..

Sent from my iPhone

On Oct 4, 2019, at 22:09, Lelio Fulgenzi <lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>> wrote:



Darn. Double darn.

Let’s hope webex offers up custom domain registration for devices soon.

‘Cause room123 at acme.rooms.webex.com<mailto:room123 at acme.rooms.webex.com> is a bit much.

-sent from mobile device-

Lelio Fulgenzi, B.A. | Senior Analyst
Computing and Communications Services | University of Guelph
Room 037 Animal Science & Nutrition Bldg | 50 Stone Rd E | Guelph, ON | N1G 2W1<x-apple-data-detectors://1/0>
519-824-4120 Ext. 56354<tel:519-824-4120;56354> | lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>

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On Oct 4, 2019, at 9:05 PM, Ryan Huff <ryanhuff at outlook.com<mailto:ryanhuff at outlook.com>> wrote:

What it sounds like you are trying to do to me, is allow the call to ultimately setup with a URI different than the URI that was dialed, without the calling party being the wiser.

DNS won’t be able to do anything with regards to that I don’t think, because it really sounds like you’re trying to manipulate/transform the called URI, and you’ll need something to interact with the SIP message stack for that I’d think.

You can create a round robin A record, that resolves to multiple IP addresses, so when the client looks up the DNS SRV, it receives multiple targets to try before considering the SRV target “unreachable” (SRV weights and priorities determine the ordering of the target addresses resolved for the client). However, this won’t have the ability to change the called URI, which is ultimately what I think you’re attempting in the scenario (DNS and SIP messages are on different networking layers).

As Dave mentioned below, Expressway or a LUA script (sip normalization) in CUCM seems to be uniquely qualified for what you’re wanting to do.

Sent from my iPhone

On Oct 4, 2019, at 20:40, Lelio Fulgenzi <lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>> wrote:



I’ve seen some references to Cisco SIP proxy server.

Would that help?

-sent from mobile device-

Lelio Fulgenzi, B.A. | Senior Analyst
Computing and Communications Services | University of Guelph
Room 037 Animal Science & Nutrition Bldg | 50 Stone Rd E | Guelph, ON | N1G 2W1<x-apple-data-detectors://1/0>
519-824-4120 Ext. 56354<tel:519-824-4120;56354> | lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>

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On Oct 4, 2019, at 7:46 PM, Ryan Huff <ryanhuff at outlook.com<mailto:ryanhuff at outlook.com>> wrote:

According to RFC 2782 (https://www.ietf.org/rfc/rfc2782.txt<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Frfc%2Frfc2782.txt&data=02%7C01%7C%7C9b720a4af69b41bebb5008d7493d7691%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637058400631429128&sdata=OAmRMMzoz0YfzhuHqJuiHYHNI9JHtJrfTTEeesLBbDg%3D&reserved=0>), it does not, under the “Target Definition”; “there must be one or more address records for this name, the name must not be an alias”.

However, I can tell you that I have used a CNAME in the SRV target field before, and it appeared to work at the time. Still, depending on the application, doing so could potentially cause some weird issue with regards to PTR or something.

Sent from my iPhone

On Oct 4, 2019, at 19:10, Brian Meade <bmeade90 at vt.edu<mailto:bmeade90 at vt.edu>> wrote:


I don't think DNS SRV records support CNAME.  Even then, it would only change where it was sent to and not the SIP headers.

On Fri, Oct 4, 2019 at 12:26 PM Lelio Fulgenzi <lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>> wrote:
Yeah – I’d want this to happen all within DNS. But of course, in a supported fashion. I’m not interested in spending time modifying infrastructure at this time.

I’ve done some searching, and there’s talk of RR records, but we haven’t found much documentation.


---
Lelio Fulgenzi, B.A. | Senior Analyst
Computing and Communications Services | University of Guelph
Room 037 Animal Science & Nutrition Bldg | 50 Stone Rd E | Guelph, ON | N1G 2W1
519-824-4120 Ext. 56354 | lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>

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<image001.png>

From: Dave Goodwin <dave.goodwin at december.net<mailto:dave.goodwin at december.net>>
Sent: Friday, October 4, 2019 12:09 PM
To: Lelio Fulgenzi <lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>>
Cc: cisco-voip voyp list <cisco-voip at puck.nether.net<mailto:cisco-voip at puck.nether.net>>
Subject: Re: [cisco-voip] SIP Domain substitution

Are you wanting this to all happen within DNS instead of happening within a SIP UA? As far as I understand, if DNS redirected somewhere (SRV or CNAME record for example) it would not change the destination URI the originator is trying to reach. The SIP protocol has redirection codes (such as 301 or 302) but whether or how you might be able to use them depends on the SIP UAs being used.

You might also be able to use something like a SIP normalization script (CUCM), SIP profiles (CUBE), or maybe search pattern replacements (Expressway) to just translate the domain as calls flow in/out. I'm guessing what might be feasible without knowing more of the picture.

On Fri, Oct 4, 2019 at 11:10 AM Lelio Fulgenzi <lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>> wrote:

Does SIP allow for domain name substitution?

By this I mean, instead of advertising or dialing coyote at phones.america.acmemanufacturing.com<mailto:coyote at phones.america.acmemanufacturing.com> I want to use coyote at zing.com<mailto:coyote at zing.com>

But I don’t want to have to reorganize and reprogram anything.

I just want the DNS to say, “hey, use this domain instead and try again.”
-sent from mobile device-

Lelio Fulgenzi, B.A. | Senior Analyst
Computing and Communications Services | University of Guelph
Room 037 Animal Science & Nutrition Bldg | 50 Stone Rd E | Guelph, ON | N1G 2W1
519-824-4120 Ext. 56354<tel:519-824-4120;56354> | lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>

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