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Catalyst 2940 Switch Software Configuration Guide
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Chapter4 Assigning the Switch IP Address and Default Gateway Assigning Switch Information
Understanding DHCP-Based Autoconfiguration
The DHCP provides configuration information to Internet hosts and internetworking devices. This
protocol consists of two components: one for delivering configuration parameters fro m a DHC P ser ver
to a device and a mechanism for allocating network addresses to devices. DHCP is built on a
client-server model, in which designated DHCP servers allocate network addresses and deliver
configuration parameters to dynamically configured devices.
During DHCP-based autoconfiguration, your switch (DHCP client) is automatically configured at
startup with IP address information and a configuration file.
With DHCP-based autoconfiguration, no DHCP client-side configuration is needed on your switch.
However, you need to configure the DHCP server for various lease options associated with IP addresses.
If you are using DHCP to relay the configuration file location on th e net work, you mig ht a lso ne ed to
configure a Trivial File Transfer Protocol (TFTP) server and a Domain Name System (DNS) server.
The DHCP server can be on the same LAN or on a different LAN than the switch. If the DHCP server
is running on a different LAN, you should configure a DHCP relay. A relay device forwards b roadc ast
traffic between two directly connected LANs. A router does not forward broadcast packets, but it
forwards packets based on the destination IP address in the received packet.
DHCP-based autoconfiguration replaces the BOOTP client functionality on your switch.

DHCP Client Request Process

When you boot your switch, the switch automatically requests configuration information from a DHCP
server only if a configuration file is not present on the switch.
DHCP autoconfiguration does not occur under these conditions:
•When a configuration file is present and the service config global configuration command is
disabled on the switch.
•When a configuration file is present and the service config global configuration comman d is enabled
on the switch. In this case, the switch broadcasts TFTP requests for the configuration file.
Telnet password No password is defined.
Cluster command switch functionality Disabled.
Cluster name No cluster name is defined.
Table4-1 Default Switch Information (continued)
Feature Default Setting