Configuring The Dns; Configuring The Relay Device - Cisco 2950 - Catalyst Switch Configuration Manual

Chapter 5 Assigning the Switch IP Address and Default Gateway

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 an 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
Figure 5-2
DHCP server
78-11380-10
Figure 5-2, configure the router interfaces as follows:
Relay Device Used in Autoconfiguration
Switch
(DHCP client)
10.0.0.2
10.0.0.1
20.0.0.2 20.0.0.3
TFTP server
Cisco router
(Relay)
20.0.0.1
20.0.0.4
DNS server
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
Assigning Switch Information
5-7