Allied Telesis AlliedWare NetScreen Routers User Manual
How To |
U s e D y n a m i c D N S To A l l o w Yo u To H o s t S e r v e r s
Behind A Dynamically-Assigned Public IP Address
Allied Telesis routers feature a dynamic DNS client, which allows you to host web domains,
FTP servers, and mail servers behind a dynamically-assigned public IP address that periodically
changes. The dynamic DNS client works with the service provided by DynDNS.com
(www.dyndns.com). When the public IP address changes, the client notifies DynDNS.com of
the change.
What information will you find in this document?
This How To Note begins with essential background information, in the following sections:
• “DynDNS.com hostnames” on page 2
• “DNS server assignment” on page 3
Then it describes the example configuration, in the following sections:
• “Configuring dynamic DNS” on page 3:
• “Network diagram” on page 4
• “Configure the network and firewall” on page 4
• “Configure dynamic DNS” on page 7
• “Check dynamic DNS configuration” on page 9
• “Troubleshooting” on page 11
Which products and software version does it apply to?
This configuration applies to the following Allied Telesis routers, running Software Version
2.9.1 or later:
• AR4
• AR440S, AR44
• AR750S, AR750S-DP, AR770S
1
5S
1
S, AR442S
C613-16100-00 REV A
www.alliedtelesis.com
DynDNS.com hostnames
In order to use the dynamic DNS client on the router, you first need to register at least one
hostname (actually a fully qualified domain name—FQDN) with DynDNS.com.
The dynamic DNS client can work with the following three hostname types from
DynDNS.com:
• Dynamic Hosts
This is the option to use if you don't own a domain name, but you want to host a server
on your network and have people reach it by entering a domain name.
Dynamic hosts are free to register with DynDNS.com, and allow you to associate a
dynamic IP address with up to five of the static domain names that DynDNS.com provide.
Dynamic host IP associations require at least one update every 35 days to prevent them
from expiring.
• Static Hosts
This is the option to use if you have a fixed IP address, you want to host a server on your
network and have people reach it by entering a domain name, but you do not want to buy
your own domain name.
Like dynamic hosts, static hosts are free to register with DynDNS.com, and allow you to
associate your public IP address with up to five of the static domain names that
DynDNS.com provides. However, static hosts are designed for use with IP addresses that
rarely or never change. This means that static host IP associations do not expire, and that
dynamic DNS updates take longer to propagate through the DNS system with static hosts.
• Custom Hosts
This is the option to use if you already own your own domain name.
Custom hosts support both static and dynamic IP addresses. For custom hosts, in addition
to automatic updates via the dynamic DNS client, DynDNS.com also provides a web-based
interface where you can make updates directly. Such direct changes propagate through the
DNS system very quickly.
Use Dynamic DNS To Allow You To Host Servers Behind A Dynamically-Assigned Public IP Address 2
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
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.
1
29 (Primary server) and 131 (secondary server) on PPP interfaces
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
• “Check dynamic DNS configuration” on page 9
Use Dynamic DNS To Allow You To Host Servers Behind A Dynamically-Assigned Public IP Address 3
Network diagram
The following figure shows the network configuration.
web
server
AR440S router
FTP
server
ppp1
(ISDN)
mail
server
ppp0
(ADSL)
ISP 1
Internet
DNS
server
ISP 2
DynDNS.com
server
ddns.eps
Configure the network and firewall
This section describes how to configure the WAN links, IP, and the firewall.
1. Specify the country
Setting the country sets the ADSL defaults. Use the command:
set system country=your-country
2. Configure the WAN links
For the primary ADSL link, use the commands:
create atm=0 over=adsl0
add atm=0 channel=1
enable adsl=0
For the backup ISDN link, use the command:
add isdn call=backup num=isdn-number-of-isp prec=out
Use Dynamic DNS To Allow You To Host Servers Behind A Dynamically-Assigned Public IP Address 4
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