The following example shows how to set up DDNS for DDNS service provider DynDNS. It is assumed for this example that you have already signed up with DynDNS). To configure the vRouter in this way, perform the following steps in configuration mode.

vyatta@R1# set service dns dynamic interface dp0p1p1 service dyndns 

vyatta@R1# set service dns dynamic interface dp0p1p1 service dyndns login vtest 

vyatta@R1# set service dns dynamic interface dp0p1p1 service dyndns password testpwd 

vyatta@R1# set service dns dynamic interface dp0p1p1 service dyndns host-name r1.company.com 

vyatta@R1# set service dns dynamic interface dp0p1p1 service dyndns host-name www.company.com 

vyatta@R1# commit OK 

vyatta@R1# show service dns dynamic
interface dp0p1p1 {
	service dyndns {
		 host-name r1.company.com
	 	host-name www.company.com
		 login vtest
		 password testpwd
	}
}

At this point, whenever the IP address on dp0p1p1 changes, the vRouter automatically logs onto the DynDNS service by using the vtest login ID and the testpwd password. It sends an update for the r1.company.com and www.company.com host names specifying the new IP address required to reach those hosts on the company.com domain. External users that query DNS for r1.company.com or www.company.com are subsequently answered with the new address from the DNS system.

Name server locations can be obtained in three ways:

• From the system name server list, defined by using the set system name-server command
• By DHCP
• By listing additional name servers by using service dns forwarding dhcp <interface>

By default, the vRouter forwards DNS requests to name servers on the system name server list plus name servers obtained through DHCP. You can override the default behavior by specifying any or all of the following:

• Specifically use system-defined name servers. To do this, use service dns forwarding system.
• Specifically use name servers received for the interface that is using DHCP client to get an IP. To do this, use service dns forwarding dhcp <interface>.
• List additional name servers by using service dns forwarding name-server <ipv4>.

These three options can be used in any combination; however, using any of them eliminates the default DNS forwarding behavior.

When DNS forwarding starts or restarts, it broadcasts a message to all the name servers in the pool and selects the first name server to answer. This name server is used unless it becomes unreachable, in which case the system sends another broadcast message to the remaining name servers in the pool.

The listening interfaces are the interfaces to which internal clients forward DNS requests. The DNS forwarding service listens for these requests and forwards them to the name server.

To set the listening interface, use service dns forwarding listen-on <interface>. You can specify more than one interface by issuing this command multiple times.

After these steps are completed, DNS forwarding is set up. At this point, the vRouter DHCP server can be used to distribute the DNS forwarding interface address to DHCP clients. (For information about setting up a DHCP server on the vRouter, see DHCP .

Scenario using DNS forwarding shows a typical scenario in which DNS forwarding is deployed. In this scenario:

• The ISP is providing dynamic IP addresses to its customers, including a vRouter (R1) through DHCP.
• The vRouter (R1) is providing DHCP service to clients on its local network.
• Local clients send DNS requests to the vRouter.
• The DNS forwarding service on the vRouter forwards the requests to the the DNS server of the ISP.

The following example shows how to set up the key parts of the vRouter for the preceding scenario. To configure the vRouter in this way, perform the following steps in configuration mode.

vyatta@R1# set interfaces dataplane dp0p1p2 address 192.168.1.254/24 

vyatta@R1# set interfaces dataplane dp0p1p1 address dhcp 

vyatta@R1# set service dhcp-server shared-network-name dp0p1p2_POOL subnet 192.168.1.0/24 start 192.168.1.100 stop 192.168.1.199 

vyatta@R1# set service dhcp-server shared-network-name dp0p1p2_POOL subnet 192.168.1.0/24 default-router 192.168.1.254 

vyatta@R1# set service dns forwarding dhcp dp0p1p1 

vyatta@R1# set service dns forwarding listen-on dp0p1p2 

vyatta@R1# set service dhcp-server shared-network-name dp0p1p2_POOL subnet 192.168.1.0/24 dns-server 192.168.1.254 

vyatta@R1# commit 

vyatta@R1# show service dns
forwarding {
	    dhcp dp0p1p1
    	listen-on dp0p1p2
}