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Chapter 10: Technical Reference
Megabit Modem 400F, 500L, 600F, and 700F User Manual 93
DNS RESOLUTION
If you want Domain Name System (DNS) resolution, you need to specify the IP address for a
device to be the DNS resolver. You can also specify another IP address to designate a second
device for a secondary DNS resolver. The DNS device maps human-readable addresses to IP
addresses. A human-readable address is one such as maggie.copro.company.com that
contains a host name and domain. The DNS resolver maps that name to the IP address that is a
numeric (four octet) value such as 192.168.30.25.
In previous versions of code, the provisioning of more than one PPP over ATM session required
the manual configuration of DNS server addresses on the host computers. Changing from one
session to another session also required manual configuration. This is because different sessions
required different DNS server addresses, and the modem did not have a way to handle the DNS
server address on a session by session basis.
DNS Relay solves this problem. With DNS Relay, the DNS server addresses are configured on
a per session basis and all the hosts on the LAN have their DNS server addresses configured to
the same address, the LAN IP address of the modem. Therefore, multiple hosts in different
sessions configured for DHCP can receive the modem’s LAN IP address as the DNS server
address. When a host sends out a DNS message to the modem, the modem looks up the source
IP address in the User Assignment Table to determine the host’s session and the DNS server for
that session. The modem replaces the destination IP address of the frame with the DNS server
address configured for that session and sends the frame on its way.
TFTP SERVER
Trivial File Transfer Protocol (TFTP) is the TCP/IP standard for file transfer. It provides
the service with minimal capability and minimal overhead. TFTP uses UDP for
connectionless delivery.
A TFTP Server is a device on the network which stores files that other IP devices can access for
file transfer using the TFTP protocol. The Megabit Modem is one of these IP devices and uses
theTFTP server to download updated software in binary format.
Typical TFTP servers are not dedicated only for file transfer. Frequently, Microsoft Windows
desktops are used to store the binary files. To create a TFTP server, several shareware programs
are available through the Internet. Once you have selected and installed the TFTP server
software, configure it to share a directory containing the binary files. To configure the Megabit
Modem to access the TFTP server, see Chapter 9 on page 77.