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Switch Memory and Configuration
Automatic Configuration Update with DHCP Option 66
Multiple Servers serving Multiple VLANs • Each DHSP-enabled VLAN interface initiates DHCPDISCOVER and
receives one or more DHCPOFFER messages.
Scenario Behavior
• Each interface accepts the best offer.
• Option 66 is processed only for the interface belonging to the primary
VLAN.
Multi-homed Server serving Multiple VLANs • The switch perceives the multi-homed server as multiple separate
servers.
• Each DHCP-enabled VLAN interface initiates DHCPDISCOVER and
receives one DHCPOFFER message.
• Each interface accepts the offer.
• Option 66 is processed only for the interface belonging to the primary
VLAN.
Operating Notes
Replacing the Existing Configuration File: After the DHCP client down-
loads the configuration file, the switch compares the contents of that file with
the existing configuration file. If the content is different, the new configuration
file replaces the existing file and the switch reboots.
Option 67 and the Configuration File Name: Option 67 includes the name
of the configuration file. If the DHCPACK contains this option, it overrides the
default name for the configuration file (switch.cfg)
Global DHCP Parameters: Global parameters are processed only if received
on the primary VLAN.
Best Offer: The “Best Offer” is the best DHCP or BootP offer sent by the
DHCP server in response to the DHCPREQUEST sent by the switch. The
criteria for selecting the “Best Offer” are:
• DHCP is preferred over BootP
• If two BootP offers are received, the first one is selected
• For two DHCP offers:
– The offer from an authoritative server is selected
– If there is no authoritative server, the offer with the longest lease
is selected
Log Messages
The file transfer is implemented by the existing TFTP module. The system logs
the following message if an incorrect IP address is received for Option 66:
“Invalid IP address <ip-address> received for DHCP Option 66”
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