A23. What Is Bootp/Dhcp - ZyXEL Communications ZyWALL 5 Support Notes

ZyWALL 5 Support Notes
If you are not able to get the Internet IP from the ISP, check which authentication method your ISP uses and
troubleshoot the problem as described below.
1. Your ISP checks the 'MAC address'
Some ISPs only provide an IP address to the user with an authorized MAC address. This authorized MAC
can be the PC's MAC which is used by the ISP for the authentication. So, if a new network card is used or
the ZyWALL is attached to the cable modem directly, the ISP will reject the DHCP discovery from this
MAC, thus no IP is assigned by the ISP.
The ZyWALL supports to clone the MAC from the first PC the ISP installed to be its WAN MAC. To
clone the MAC from the PC you need to enter that PC's IP in WAN menu of the ZyWALL web
configurator.
2. Your ISP checks the 'Host Name'
Some ISPs take advantage of the 'host name' message in a DHCP packet such as @home to do the
authentication. When first installing, the ISP's tech people configure the host name as the 'Computer Name' of
the PC in the 'Networking' settings. When the ZyWALL is attached to the cable modem to connect to the ISP,
we should configure this host name in the ZyWALL's system (menu 1).

A23. What is BOOTP/DHCP?

BOOTP stands for Bootstrap Protocol. DHCP stands for Dynamic Host Configuration Protocol. Both are
mechanisms to dynamically assign an IP address for a TCP/IP client by the server. In this case, the ZyWALL
Internet Access Sharing Router is a BOOTP/DHCP server. WinXP/2000 and WinNT clients use DHCP to
request an internal IP address, while WFW and WinSock clients use BOOTP. TCP/IP clients may specify their
own IP or utilize BOOTP/DHCP to request an IP address.
A24. What is DDNS?
The Dynamic DNS service allows you to alias a dynamic IP address to a static hostname, allowing your
computer to be more easily accessed from various locations on the Internet. To use the service, you must
first apply an account from several free Web servers such as WWW.DYNDNS.ORG.
Without DDNS, we always tell the users to use the WAN IP of the ZyWALL to reach our internal server.
It is inconvenient for the users if this IP is dynamic. With DDNS supported by the ZyWALL, you apply a
DNS name (e.g., www.zyxel.com.tw) for your server (e.g., Web server) from a DDNS server. The outside
users can always access the web server using the www.zyxel.com.tw regardless of the WAN IP of the
ZyWALL.
When the ISP assigns the ZyWALL a new IP, the ZyWALL updates this IP to DDNS server so that the
server can update its IP-to-DNS entry. Once the IP-to-DNS table in the DDNS server is updated, the DNS
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