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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 4 Assigning the Switch IP Address and Default Gateway
Assigning Switch Information
For the switch to successf ull y downloa d a configura tion file, the TFTP ser ver must contain one or m ore
configur ation files in its base direct ory. The files ca n incl ude t hese file s:
•The co nfiguration file named in the DHCP re ply (the ac tual switc h configurati on file).
•The net work-conf g or the ciscon et.cf g file (known as the default configurat ion files).
•The ro uter-confg or the ciscortr.cfg file (T hese files cont ain comm ands com mon to al l switches .
Normally, if the DHCP and TFTP servers are properly configured, these files are not accessed.)
If you spe cify the TF T P server na me i n t he D HC P s erver-lease da tabase , you m ust a lso co nfigure 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 earlier), a relay must be configured to forward the TFTP packets to the
TFTP server. For more informa tion, se e the “Configuring the Re lay D evice” section on page 4-6. The
preferred s olution 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 T FTP ser ver n ame- to-I P a ddr ess m ap on the DN S s er ver. The T FTP ser ver con ta ins the
configuration files for the switch.
You can configure th e IP addresse s of the DNS servers in the lease dat abase of the DH CP server from
where t he DHCP replies will r etriev e them . You can e nter up to two DNS server I P addresses in the lea se
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 re lay device when a switc h sends broadc ast packets tha t need to be respo nded to
by a host on a different LAN. Examples of broadcast packets that the switch might send are DHCP, DNS,
and in so me c as es, T FTP packet s. You must con figure t his re lay device t o fo rwar d rec eived broa dcast
packets on an interface to the destination host.
If the r ela y device is a Cisc o ro uter, enabl e I P rou ting (ip routing global c onfigurat ion co mm an d), an d
configure hel per a ddre sses by usi ng the ip helper-address interface c on figura ti on co mm an d.
For exam ple, in Figure 4-2, configure the router inte rfaces as foll ows:
On in te rfa ce 1 0. 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 in te rfa ce 2 0. 0.0 .1
router(config-if)# ip helper-address 10.0.0.1