RHEL CUPS print server rejecting requests with "Invalid Host" message

Issue

• After the Printer server upgrade to RHEL6, no print jobs work. The CUPS error log (/var/log/cups/error_log) shows errors like the following:

  E [11/Nov/2014:16:57:31 -0600] Request from "10.1.2.3" using invalid Host: field "corp.example.com".
  

  We have two printer servers that use an F5 load balancer.

• We use the CUPS client.conf file which let the local client print to an external CUPS server. When i put the hostname of the remote CUPS server in client.conf (i.e. "ServerName cups.example.com") and try to print it says "lpr: bad-request". If I put the IP_address of the remote CUPS server in client.conf (i.e. "ServerName 10.1.2.3"), then everything works fine.

• Attempting to access the CUPS Web user interface of a remote system using the host name results in a "Bad Request" message in the Web Browser. However, if the IP address of the system is used, then access is normal.