Configuring The Dns; Configuring The Relay Device - Cisco 3845 - Security Bundle Router Software Manual

Assigning Switch Information
these files: network-config, cisconet.cfg, hostname.config, or hostname.cfg, where hostname is the
switch's current hostname. The TFTP server addresses used include the specified TFTP server address
(if any) and the broadcast address (255.255.255.255).
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 these files:
•
•
•
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 to be used 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 previously), a relay must be configured to forward the TFTP packets to
the TFTP server. For more information, see the
preferred solution is to configure the DHCP server with all the required information.

Configuring the DNS

The DHCP server 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 from
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, also referred to as a relay agent, when a switch sends broadcast
packets that require a response from a host on a different LAN. Examples of broadcast packets that the
switch might send are DHCP, DNS, and in some cases, TFTP packets. You must configure this relay
device to forward received broadcast packets on an interface to the destination host.
If the relay device is a Cisco router, enable IP routing (ip routing global configuration command), and
configure helper addresses by using the ip helper-address interface configuration command.
For example, in
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
Cisco ME 3800X and 3600X Switch Software Configuration Guide
3-8
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.)
Figure 3-2, configure the router interfaces as follows:
Chapter 3 Assigning the Switch IP Address and Default Gateway
"Configuring the Relay Device" section on page 3-8. The
OL-23400-01