Configuring The Relay Device - Cisco Catalyst 2950 Software Manual

Chapter 6 Configuring the System
Changing IP Information
You can specify a default domain name that the software uses to complete domain name requests. You
can specify either a single domain name or a list of domain names. When you specify a domain name,
any IP host name without a domain name will have that domain name appended to it before being added
to the host table.
If your network devices require connectivity with devices in networks for which you do not control name
assignment, you can assign device names that uniquely identify your devices within the entire
internetwork. The DNS accomplishes this task. This service is enabled by default.
The switch uses the DNS server to resolve the TFTP server name to a TFTP-server 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 must 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 relay device or router. For more information, see the
"Configuring the Relay Device" section on page 6-6.
For CLI procedures, refer to the Cisco IOS Release 12.1 documentation on Cisco.com for additional
information and CLI procedures.

Configuring the Relay Device

You need to use a relay device if the DHCP, DNS, or TFTP servers are on a different LAN than the
switch. You must configure this relay device to forward received broadcast packets on an interface to the
destination host. This configuration ensures that broadcasts from the DHCP client can reach the DHCP,
DNS, and TFTP servers and that broadcasts from the servers can reach the DHCP client.
If the relay device is a Cisco router, you enable IP routing (ip routing global configuration command)
and configure it with helper addresses by using the ip helper-address interface configuration command.
For example, in Figure 6-2, you configure the router interfaces as follows:
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
Catalyst 2950 Desktop Switch Software Configuration Guide
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