Dns server assignment, Configuring dynamic dns – Allied Telesis AlliedWare NetScreen Routers User Manual
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Use Dynamic DNS To Allow You To Host Servers Behind A Dynamically-Assigned Public IP Address
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DNS server assignment
For the dynamic DNS process on the router to work, the router itself must be able to
resolve the domain name dyndns.com. Therefore, the router needs to know the address of at
least one DNS server. The router can learn the addresses of DNS servers dynamically from
your ISP, or you can configure them statically.
Dynamically
When ISPs supply IP address settings dynamically, they mostly supply DNS server settings as
well. They do this by setting one of the following:
•
DHCP option 6 on Eth and VLAN interfaces
•
IPCP options 129 (Primary server) and 131 (secondary server) on PPP interfaces
You can check if your router has dynamically-assigned name servers, and if so, what the
server addresses are, by using the command:
show ip dns
Dynamically-assigned servers are identified by an * in the Domain column of the output of
this command.
If necessary, you can force the router to learn DNS servers over a particular Eth, PPP or
VLAN interface. Use the command:
add ip dns interface=interface
Statically
If your ISP does not assign DNS servers dynamically, you need to enter their addresses
statically. Use the command:
add ip dns primary=ipadd secondary=ipadd
If you manually configure the DNS servers and you have a backup connection to a different
ISP, you may need to set up triggers so that when the primary WAN connection fails, the
router is re-configured with the correct DNS servers for the backup connection.
Configuring dynamic DNS
In this example, an AR440S connects to the Internet through a primary ADSL connection to
ISP 1, with a backup ISDN connection to ISP 2. The AR440S router also acts as a firewall.
Steps that relate to the backup link are labelled, so you can avoid them if you have a single
connection.
To configure this example, follow the steps in the following sections:
•
“Configure the network and firewall” on page 4
•
“Configure dynamic DNS” on page 7
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