Explanation
There are two types of subscriptions: periodic and on-change. With periodic subscription, data is streamed out to the destination at the configured interval. It continuously sends data for the lifetime of that subscription.
With on-change, data is published only when a change in the data occurs such as when an interface or OSPF neighbor goes down.https://developer.cisco.com/docs/ios-xe/#!streaming-telemetry-quick-start-guide/streaming-telemetry

When configuring DHCP snooping, follow these guidelines:
DHCP snooping is not active until you enable the feature on at least one VLAN, and enable DHCP globally on the switch.
Before globally enabling DHCP snooping on the switch, make sure that the devices acting as the DHCP server and the DHCP relay agent are configured and enabled.
If a Layer 2 LAN port is connected to a DHCP server, configure the port as trusted by entering the "ip dhcp snooping trust" interface configuration command.
If a Layer 2 LAN port is connected to a DHCP client, configure the port as untrusted by entering the no ip dhcp snooping trust interface configuration command.
Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SX/configuration/guide/ book/snoodhcp.html