Explanation

There are four messages sent between the DHCP Client and DHCP Server: DHCPDISCOVER, DHCPO FFER, DHCPREQUEST and DHCPACKNOWLEDGEMENT.
This process is often abbreviated as DORA (for Discover, Offer, Request, Acknowledgement).

Explanation
An EEM policy is an entity that defines an event and the actions to be taken when that event occurs. There are two types of EEM policies: an applet or a script. An applet is a simple form of policy that is defined within the CLI configuration. answer 'event manager applet ondemand event register action 1.0 syslog priority critical msg 'This is a message from ondemand'
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There are two ways to manually run an EEM policy. EEM usually schedules and runs policies on the basis of an event specification that is contained within the policy itself. The event none command allows EEM to identify an EEM policy that can be manually triggered. To run the policy, use either the action policy command in applet configuration mode or the event manager run command in privileged EXEC mode.
Reference: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/eem/configuration/xe-3s/eem-xe-
3s-book/eem-policy-cli.html