Purpose Of The Dns Server - Cisco Catalyst 2960 series Configuration Manual

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 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 LAN or on a different LAN from the switch. If it is on a different LAN,
the switch 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 switch obtains its configuration information in these ways:
• The IP address and the configuration filename is reserved for the switch and provided in the DHCP reply
(one-file read method).
The switch receives its IP address, subnet mask, TFTP server address, and the configuration filename
from the DHCP server. The switch 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.
• The IP address and the configuration filename is reserved for the switch, but the TFTP server address
is not provided in the DHCP reply (one-file read method).
The switch receives its IP address, subnet mask, and the configuration filename from the DHCP server.
The switch 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.
• Only the IP address is reserved for the switch and provided in the DHCP reply. The configuration
filename is not provided (two-file read method).
The switch receives its IP address, subnet mask, and the TFTP server address from the DHCP server.
The switch sends a unicast message to the TFTP server to retrieve the network-confg or cisconet.cfg
default configuration file. (If the network-confg file cannot be read, the switch reads the cisconet.cfg
file.)
The default configuration file contains the hostnames-to-IP-address mapping for the switch. The switch
fills its host table with the information in the file and obtains its hostname. If the hostname is not found
in the file, the switch uses the hostname in the DHCP reply. If the hostname is not specified in the DHCP
reply, the switch uses the default Switch as its hostname.
After obtaining its hostname from the default configuration file or the DHCP reply, the switch reads the
configuration file that has the same name as its hostname (hostname-confg or hostname.cfg, depending
on whether network-confg or cisconet.cfg was read earlier) from the TFTP server. If the cisconet.cfg
file is read, the filename of the host is truncated to eight characters.
If the switch cannot read the network-confg, cisconet.cfg, or the hostname file, it reads the router-confg
file. If the switch cannot read the router-confg file, it reads the ciscortr.cfg file.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
Information About Performing Switch Setup Configuration
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