Cisco OL-4015-08 User Manual page 502

Chapter 23 Router Properties
Dynamic DNS Methods
IETF
IETF is a dynamic DNS method type that updates a DNS server with changes to
the associated interface's IP address.
If using IETF, configure a DNS server for the router in Configure > Additional
Tasks > DNS.
Cisco Router and Security Device Manager Version 2.2 User's Guide
23-28
OL-4015-08