How does Jabber pick which CUCM to use for UDS?

[Mark Lyman]

In our environment, we have 5 subscribers.  We are connecting into our CUCM environment over Expressway.

We use UDS for directory. 

One of our employees was having directory issues.  We looked at the connections and her Jabber was connecting to ucmsub05 while mine was connected to ucmsub03.  With that information we were able to resolve the issue.

However, I have no idea why her Jabber chose ucmsub05 and mine chose ucmsub03.  I can't even find a place to set that.  Nor can I find any documentation as to how Jabber decides which CUCM to use for UDS.

Any ideas?

[Jaime Valencia]

I'm not completely sure, from what I know, it uses the _cisco-uds SRV in first place to locate the servers, and it also uses the CUCM groups.

Does either of those configs matches what you're seeing?

[Mark Lyman]

I know for sure it doesn't use the UCM Groups as ucmsub05 is not part of that user's group.

As for the DNS side... gonna have to think about that for a bit.

The Jabber client is connecting through the Expressway because its out on the internet.  All external DNS records only point to the Expressway.  So it must be the Expressway that is telling the Jabber client where to get its UDS from.  And then I can only guess that the UDS lookups are being tunneled through the Expressway somehow as ucmsub05 is only reachable internally, and the user has no VPN established.

Even my own Jabber client is connected via Expressway and Im seeing ucmsub03 as my UDS which is only accessible internally - so Im guessing that lookup is being tunneled or proxied by Expressway somehow.  I just dont know the process that was taken to tell it ucmsub03 (although in both my and the other user's case, ucmsub03 is the primary server in the UCM group).

[Jaime Valencia]

Yes, if you debug the login process from the EXP-C, you'll see it does lookup the SRV records for the UC apps.

[Mark Lyman]

Ok, so that much makes sense.  I can understand how the lookup works.

I still don't get how a CUCM gets chosen and assigned to a Jabber client for UDS lookups.  Or in this case, the proxied registration at Expressway.

You have been very helpful and I will continue to debug and figure it out.  I just gots to know!

[Ayodeji Okanlawon]

Mark,

There are two things to know when it comes to UDS discovery

1. Your cisco-uds SRV is used to discover the UDS servers that will be used for initial service discovery

2. Once Jabber finds the UDS server, it then queries the servers to discover the actual UDS servers available in the home cluster of the user. You cant influence which UDS server is used, it is random

3. All traffic for MRA is proxied through expressway. Your UDS servers are not usually reachable externally.