Purpose Of The Dns Server; How To Obtain Configuration Files - Cisco Catalyst 9400 System Management Configuration Manual

Performing Device Setup Configuration
and TFTP server addresses. The files include the specified configuration filename (if any) and these files:
network-config, cisconet.cfg, hostname.config, or hostname.cfg, where hostname is the device'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 device 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:
• The configuration file named in the DHCP reply (the actual device 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 device. Normally,
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 device, or if it is to be accessed by the device
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.
The preferred solution is to configure the DHCP server with all the required information.

Purpose of the DNS Server

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 device.
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 LAN or on a different LAN from the device. If it is on a different LAN,
the device must be able to access it through a router.

How to Obtain Configuration Files

Depending on the availability of the IP address and the configuration filename in the DHCP reserved lease,
the device obtains its configuration information in these ways:
• The IP address and the configuration filename is reserved for the device and provided in the DHCP reply
• The IP address and the configuration filename is reserved for the device, but the TFTP server address is
• Only the IP address is reserved for the device and provided in the DHCP reply. The configuration filename
if the DHCP and TFTP servers are properly configured, these files are not accessed.)
(one-file read method).
The device receives its IP address, subnet mask, TFTP server address, and the configuration filename
from the DHCP server. The device sends a unicast message to the TFTP server to retrieve the named
configuration file from the base directory of the server and upon receipt, it completes its boot up process.
not provided in the DHCP reply (one-file read method).
The device receives its IP address, subnet mask, and the configuration filename from the DHCP server.
The device sends a broadcast message to a TFTP server to retrieve the named configuration file from
the base directory of the server, and upon receipt, it completes its boot-up process.
is not provided (two-file read method).
System Management Configuration Guide, Cisco IOS XE Bengaluru 17.4.x (Catalyst 9400 Switches)
Purpose of the DNS Server
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