Configuring The Dns Server; Configuring The Relay Device - Cisco 4500M Software Manual

Chapter 3 Configuring the Switch for the First Time
For the switch to successfully download a configuration file, the TFTP server must contain one or more
configuration files in its base directory. The files can include the following:
•
•
•
If you specify the TFTP server name in the DHCP server-lease database, you must also configure the
TFTP server name-to-IP-address mapping in the DNS-server database.
If the TFTP server you plan to use is on a different LAN from the switch, or if it is to be accessed by the
switch through the broadcast address (which occurs if the DHCP server response does not contain all the
required information described earlier), a relay must be configured to forward the TFTP packets to the
TFTP server. For more information, see the
preferred solution is to configure either the DHCP server or the DHCP server feature running on your
switch with all the required information.

Configuring the DNS Server

The DHCP server, or the DHCP server feature running on your switch, uses the DNS server to resolve
the TFTP server name to an IP address. You must configure the TFTP server name-to-IP address map on
the DNS server. The TFTP server contains the configuration files for the switch.
You can configure the IP addresses of the DNS servers in the lease database of the DHCP server where
the DHCP replies will retrieve them. You can enter up to two DNS server IP addresses in the lease
database.
The DNS server can be on the same or on a different LAN as the switch. If it is on a different LAN, the
switch must be able to access it through a router.

Configuring the Relay Device

You must configure a relay device to forward received broadcast packets to the destination host whenever
a switch sends broadcast packets to which a host on a different LAN must respond. Examples of such
broadcast packets are DHCP, DNS, and in some cases, TFTP packets.
If the relay device is a Cisco router, enable IP routing (ip routing global configuration command), and
configure helper addresses (ip helper-address interface configuration command). For example, in
Figure
On interface 10.0.0.2:
router(config-if)# ip helper-address 20.0.0.2
router(config-if)# ip helper-address 20.0.0.3
router(config-if)# ip helper-address 20.0.0.4
On interface 20.0.0.1
router(config-if)# ip helper-address 10.0.0.1
OL-6696-01
The configuration file named in the DHCP reply (the actual switch configuration file).
The network-confg or the cisconet.cfg file (known as the default configuration files).
The router-confg or the ciscortr.cfg file. (These files contain commands common to all switches.
Normally, if the DHCP and TFTP servers are properly configured, these files are not accessed.)
3-2, configure the router interfaces as follows:
Configuring DHCP-Based Autoconfiguration
"Configuring the Relay Device" section on page
Software Configuration Guide—Release 12.2(25)EW
3-5. The
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