Impact of wrong DNS in DHCP scope for CCM

[iptuser55]

We recently deployed some phones at a new site  which were displaying  error messages on the screen

The initial issue was that Option 150 as not set up - resolved-

Phone now seemed to register to CCM (8.6) - IP address located to phone but CCM was showing rejected  on the phone page 

Phone displayed error  messages "Db config." and "Security"  

• Db Config looked like it was that no phone was configured/MAC address, phone type etc  - incorrect double checked all ok

Other could be replication between Cluster but again all ok

• Security error - Led me to look at the security trust list and delete it and as normally this solves the problem

The actual issue/resolution  was incorrect DNS name in the Option 15 of the scope - e.g xxxx.net instead of xxx.com 

Why would this lead to the above issues, I thought the main requirement was the 150 for the TFTP 

Any thoughts, answers

Many thanks

[Marcelo Morais]

Hi iptuser55,

 the IP Phone receives the TFTP IP Addr from the DHCP packet. The TFTP sends the list of CUCMs that the IP Phone should register to.

 Probably, you configure DNS in your CUCM's Cluster and the IP Phone is probably receiving something like: <CUCM Hostname>@xxx.com ... because of the DNS incorrect configuration it can't reach any CUCM's.

Hope this helps.

[EmilTaghiyev]

Best solution is using IP Address instead of domain name

[iptuser55]

The issue was that there was an incorrect DNS option 15 given out e.g mycompany.com  instead of the correct one of mycompany.com, Option 150 was an IP as normal 

I think the issue was as follows

Our CCM`s have host names such XXX-CMSUB1, XXX-CMSUB2 etc instead of IP address- before I joined. If my thinking is correct the phone received its TFTP as normal and was provided with the CM Group but in our case the group contained Host names instead of IP address. The Host names were then added to the Option 15 DNS    and so the phones tried to look for CCM`s at XXX-CMSUB1.mycompnaya.net and XXX-CMSUB2.mycompanya.net which failed since DNS has the CCM`s as XXX-CMSUB1.mycompnaya.com and XXX-CMSUB2.mycompanya.com

Does this make sense , if so why the Security and db config issue unless these are standard error messages?