Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds: .!!!!Success rate is 80 percent (4/5), round-trip min/avg/max = 1/2/4 ms Hot Coffee# Hot Coffee#sh hosts Load for five secs: 1%/0%; one minute: 0%; five minutes: 0% Time source is NTP, .811 CDT Tue Aug 13 2013 Default domain is Name/address lookup uses domain service Name servers are 172.16.1.5 Codes: UN - unknown, EX - expired, OK - OK, ??interface Loopback0 ip address .254 255.255.255.252 ! The Dynamic DNS Support for Cisco IOS Software feature enables Cisco IOS software devices to perform Dynamic Domain Name System (DDNS) updates to ensure that an IP host DNS name is correctly associated with its IP address.It can also be used in private networks as well and is heavily used in many private organizational networks.This article takes a look at what the DNS is, what it provides for a “normal” Internet user and finishes up with some methods of configuring DNS on Cisco equipment.The DHCP server could be impacted minimally because of the time and memory needed in order to set up the DDNS update and get things started.
Even if the update is done before sending the ACK to the client, it does not delay processing of other DHCP requests.
It provides two mechanisms to generate or perform DDNS: the IETF standard as defined by RFC 2136 and a generic HTTP using various DNS services.
With this feature, you can define a list of hostnames and IP addresses that will receive updates, specify an update method, and specify a configuration for Dynamic Host Configuration Protocol (DHCP) triggered updates.
That config makes the router do a forward lookup when we ping, and reverse lookup under show commands that return ip addresses.
When we do a "show user", the router does a reverse lookup for every one of the source ip addresses.