IOS/IOS-XE DNS SRV record lookup using part of the called number?

[Elliot Dierksen]

I have a customer with a bunch of voice gateways that route certain numbers to a PCCE installation. Currently the numbers are routed there via an e164 pattern map, but that is hard to maintain on 20+ separate gateways. I know in the past CUSP (Sip Proxy) had been used for this, but that product is now end of sale and no replacement was mentioned. My idea was to have a DNS SRV dial peer that tries to find SRV records for <called-number>.customer.com and and route the call based on SRV records if found. I would have a less preferred dial peer that routes the calls to a CUCM cluster. Is there any way to wild card that into the DNS SRV record lookup in a dial peer? I am open to other ideas too for CUSP replacements.

[Jonathan Schulenberg]

I’m not aware of a DNS server that could handle wildcard subdomains as you describe. That would be worthy of a blog article if you can figure it out though.

Another idea is using ENUM instead of SRV. CUBE has some support for it - although I have never used it.

Unified Border Element ENUM Support Configuration Example 

Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards, Chapter: ENUM Enhancement per Kaplan Draft RFC  

As for a CUSP replacement, I have heard several folks look at Kamailio.

FWIW- I often host the e164-pattern-map files on a centralized NAS so there is a single source of truth. With a handful of gateways it’s easy to hop on each and issue the load command to fetch an updated file. At 20+ scale it may be worth some DevNet-style scripting to run the load command at scale. 

[Elliot Dierksen]

I was thinking about putting the contents of the pattern map on some sort of central storage. I recall seeing something that you can reference a URL for that. I don't about the gateways auto-refreshing the contents though. That wouldn't be particularly challenging to have some kind of periodic job that made the gateways refresh the URL though.

[Roger Kallberg]

For the refresh of the file you can use the kron capability in IOS to set it up to periodically perform the reload of the file at the url.

This example is from the CLACCM book.

[Elliot Dierksen]

Thanks @Roger Kallberg that is a good thought. I think I will make a post in the Contact Center forum, but I wonder what is best practice for this currently. I know CUSP was a standard part of the CCE design for some time, but that no longer a thing. My main reason for using the pattern map to select both the incoming and outgoing dial peer is the CCE wants "service survivability" on the incoming dial peer. That did odd things to the caller name for non-CCE calls, so I only want to use that where it is needed. What is considered best practice for a gateway that routes some calls to CUCM, and some calls to CVP/CCE?