This document describes an alert that might be receieved during startup of Cisco Email Security Appliance (ESA).
When booting or rebooting an Cisco Content Security Appliance appliance the below DNS-related alerts may be sent:
The Critical message is:
Failed to bootstrap the DNS resolver. Unable to contact root servers.
Please check DNS configuration and/or firewall settings.
Receiving this alert during or soon after system boot-up is not cause for concern.
The AsyncOS alerting mechanism can sometimes activate before the basic OS DNS sub systems are completely on line, causing the system to send this warning. A future version of AsyncOS will suppress this alert until the system is fully booted. However, if you receive this alert from a machine that has been running for a while, or the alert continues to be sent after the boot cycle is complete, the alert may indicate an issue
The AsyncOS alerting mechanism can sometimes activate before the basic OS DNS sub systems are completely on line, causing the system to send r firewall settings.'