Nov 25

DNS Unreachable Warning – CUCM Version 11.x

Recently upgraded a UC environement from 10.5 to 11.5. After the upgrade was complete, the CUCM Publisher server displayed a “DNS Unreachable” error upon logging into the Administration webpage.


This warning message only appeared on the CUCM Publisher and not the subscriber etc. I confirmed DNS had been configured identically for both the publisher and subscriber. I read that CUCM Version 11.x no does a couple of more network tests that have a direct impact on warning/error messages being displayed on the GUI. One of these tests is against the DNS Reverse Lookup Zone. Pre 11.x versions.. The CUCM server would check to see if a PTR record existed for the hostname, in fact this is required for CUCM installation process to succeed. In version 11.x the CUCM now also continuously checks against the Reverse Lookup Zone for mismatches and displays a warning message on the GUI. In my case, the customer had created an additional A Record for user friendly purposes called, this automatically created a PTR record. So when CUCM ran checks against the Reverse Lookup Zone, the results displayed a mismatch. Hence the warning was raised and displayed. (Although DNS was functioning perfectly)

Removing this PTR Record resolved the issue with the warning message.

I ran the command “utils diagnose test” to pin point the issue.


Mar 10

Cisco SRV Records – Quick Reference SRV 0 1 8443 (Presence Publisher/Subscriber) SRV 0 1 8443 (Publisher/Subscriber) SRV 0 0 69 (TFTP) SRV 0 0 80 (CCMCMIP) SRV 0 0 5060 (VCS Control – Internal) SRV 0 0 5060 (VCS Expressway – External) SRV 0 0 443 (Free Jabber Video) SRV 0 0 8443 (Expressway-E)

Dec 16

CUCM and IM&P Integration with SRV Records

For us Cisco techs, one of the more often than not nowadays is that have to deal with the MS world of DNS (AND Certifciate Architecture… I’ll talk about this in later articles). I’ve had a fair bit of experience with DNS in the past, so I thought I would just share a little about integrating CUCM with IM & Presence using SRV records both ways to support CUCM Clusters and IM & Presence Clusters for high availability.

DNS Configuration

Create A (Host) Records

CUCM DNS A Records

Type Hostname IP Address

IM&P DNS A Records

Type Hostname IP Address

Create SRV Records

IM&P Cluster Name:

Type Identifer Protocol Weight Priority Host
SRV _sip _tcp 10 10
SRV _sip _tcp 10 10

CUCM Cluster Name:

Type Identifer Protocol Weight Priority Host
SRV _sip _udp 10 10
SRV _sip _udp 10 10

Verify Records via NSLOOKUP

>  set q-all

The above should output the following results.

-        The SRV Records and their target hosts
-        An A record for every target host identified in the SRV record.

CUCM Configuration

SIP Trunk

  1. Navigate to Device, then select Trunks
  2. Select Add New
  3. Select SIP Trunk for Trunk Type
  4. Select Next
  5. Complete the details of the SIP Trunk as per normal.
  6. Under SIP Information, check the box  Destination Address is SRV

Note: When the checkbox is ticked, CUCM changes the outbound SIP protocol from udp to tcp.

  1. Type the IM&Presence Cluster Name. (
  2. Select Save and then reset the Trunk.

Configure SIP Publish Trunk

  1. Navigate to the Service Parameters, then Cisco CallManager.
  2. Find “IM & Presence Publish Trunk”
  3. Drop the arrow down and select the above SIP Trunk.

 IM & Presence Configuration

SRV Cluster Name

  1. Navigate to Service Parameters, then Cisco SIP Proxy.
  2. Find “SRV Cluster Name”
  3. Type the IM&Presence cluster name (
  4. Select Save

Presence Gateway

  1. Navigate to Presence, then Gateways.
  2. Select Add New
  3. Select CUCM for Presence Gateway Type.
  4. Type a Descriptive note.
  5. Type the SRV Record for the CUCM Cluster Name.

Note: Do not strip the SRV Identifier or Protocol. Example input would be

Feb 09

Configuring Basic DNS for Cisco UC

One the topics that is generally overlooked is the creation of a solid DNS architecture. These days DNS is relied upon to maintain the upkeep of any domain, in my opinion Cisco UC products are much more aligned to using DNS than the old ways of just plugging in an IP Address for each service. The project I undertake now, I’ll always ensure the DNS architecture is looked at and configured first. It’s amazing how smooth a Cisco UC implementation is with the DNS infrastructure configured according to best practices.

In this article, I will touch on DNS and records that are created to ensure a smooth initial implementation.

The Cisco Install will throw an error during install if you enable DNS Client and have not yet created the DNS A Records! I like to plan and document all the DNS Records I’ll need for the Cisco UC install in its entirety. But obviously this is not a necessity.

For all you Cisco geeks out there, we are going to spend most of time with modifying the Forward Lookup zone. This is the zone by which DNS Names are resolved to IP Addresses and just for completeness the Reverse Zone is for resolving IP Addresses to DNS Names.

Right-Click on the Forward-Lookup zone and select New Host (A or AAAA) Record.

Enter the Name of your CUCM Publisher, as you enter the name, the ‘Fully qualified domain name (fqdn) is auto populated.

Now enter the IP Address of the CUCM Publisher. Be sure to check the box “Create associated pointer (PTR) record”. This is the record that will sit in the Reverse Lookup zone.

Repeat this process for every Cisco UC server. CUCM publisher, subscribers, CUC Publisher and subscribers, IMP/CUPs publisher and subscribers, Cisco VCSc and VCSe servers etc, you get my drift.

At this point you can go ahead and install your servers without errors.