4-5
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 4 Configuring Cisco IOS Configuration Engine
Understanding Cisco IOS Agents
Understanding Cisco IOS Agents
The CNS event agent feature allows the switch to publish and subscribe to events on the event bus and
works with the Cisco IOS agent. The Cisco IOS agent feature supports the switch by providing these
features:
• Initial Configuration, page 4-5
• Incremental (Partial) Configuration, page 4-6
• Synchronized Configuration, page 4-6
Initial Configuration
When the switch first comes up, it attempts to get an IP address by broadcasting a DHCP request on the
network. Assuming there is no DHCP server on the subnet, the distribution switch acts as a DHCP relay
agent and forwards the request to the DHCP server. Upon receiving the request, the DHCP server assigns
an IP address to the new switch and includes the TFTP server IP address, the path to the bootstrap
configuration file, and the default gateway IP address in a unicast reply to the DHCP relay agent. The
DHCP relay agent forwards the reply to the switch.
The switch automatically configures t
he assigned IP address on interface VLAN 1 (the default) and
downloads the bootstrap configuration file from the TFTP server. Upon successful download of the
bootstrap configuration file, the switch loads the file in its running configuration.
The Cisco IOS agents initiate communication with the Configuration Engine by using the appropriate
Conf
igID and EventID. The Configuration Engine maps the Config ID to a template and downloads the
full configuration file to the switch.
Figure 4-2 sho
ws a sample network configuration for retrieving the initial bootstrap configuration file
by using DHCP-based autoconfiguration.
Figure 4-2 Initial Configuration Overview
TFTP
server
DHCP relay agent
default gatewayDistribution layer
Configuration
Engine
Access layer
switches
141328
DHCP
server
V
WAN
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