CCUM v.15 chnaging IP address to FQDN

[AdamG73545]

Hello,

Currently, we do have sub and pub of CCUM and CUC set up with IPs. Is it going to be a headache to change them to FQDN?

I wonder if that includes reinstalling new certs if we change IPs to FQDN? 

[Nithin Eluvathingal]

Do you mean mentioning the hostname on the server page of the CUCM instead of using the IP address?

Note: On the server page for CUCM, you can mention either the hostname or IP address, and for IMP, it’s required to use the FQDN.

I always prefer to use the IP address since using the hostname requires DNS configuration for the phone subnet, and the phones must communicate with the DNS to resolve the CUCM hostname. If there are issues with reaching the DNS, it can cause potential problems when the hostname is used.

Certificates will only be affected if you change the hostname of the device, domain, etc. Based on your requirements, it doesn’t seem like you are changing those, so the certificates should not be affecte

[AdamG73545]

Thank you Nithin,

That makes sense. But long story short, I use Expressway C&E, and seems like Cisco requires that:

1. Your CUCM is currently addressed using IP address (NOT FQDN)
1. Change CUCM Server Definition from IP Address or Hostname to FQDN Format - https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/211393-Change-CUCM-Server-Definition-from-IP-Ad.html
2. See related defects below
3. DOC: x14.2 new certificate verification with IP Addressed defined CUCM servers - https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwd34301
4. DOC: X14.2 Expressway Certificate validation for Unity for MRA Voicemail services - https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwf40332

I wonder if I can still use IPs instead of FQND and have Expressways run with no issues. 

[Maren Mahoney]

If you are planning to use the Expressways to provide MRA services, you must use FQDNs. -- Maren

[Roger Kallberg]

I would change it to FQDN and be done with it. It won't affect certificates. The DNS lookup thing outlined by @Nithin Eluvathingal is IMHO quite minimal and with predominately software clients being the trend in most situations it's anyway a needed way forward.

[Nithin Eluvathingal]

Using an IP address is suitable for deployments that use basic IP telephony. However, since you are using Expressway C & E and MRA features, it’s recommended to use the hostname instead of the IP address. For the phones and all devices that communicate with the CUCM, DNS and domain must be configured, and they must have reachability to the DNS servers.

As other peers have highlighted, end device can have the DNS and Domain details by adding  those details to the DHCP and refresh the devices for the changes to take effect.

Changing the IP address to the hostname has no effect on the certificates.

[AdamG73545]

Hmm what about the Cisco phones? Then phones need to recognize DNS of CCUM instead IP - am I right? 

[Roger Kallberg]

Yes that is right. Small/simple thing to solve, just define DNS server(s) in the DHCP scope(s) used by the phones.

[Maren Mahoney]

And to add to what @Roger Kallberg said about DNS: Adding a domain and DNS server to phone DHCP pools is pretty easy. In the 'olden days' when DNS was not robust the recommendation was to use IP addresses for your servers because DNS wasn't reliable. These days in a reasonably well-designed network DNS response times are fast enough that the phones don't generally run into any issues using FQDNs.

Maren