Switch Memory and Configuration

Automatic Configuration Update with DHCP Option 66

Possible Scenarios for Updating the Configuration File

The following table shows various network configurations and how Option 66 is handled.

Scenario

Behavior

 

 

Single Server serving Multiple VLANs

• Each DHCP-enabled VLAN interface initiates DHCPDISCOVER

 

message, receives DHCPOFFER from the server, and send

 

DHCPREQUEST to obtain the offered parameters.

 

• If multiple interfaces send DHCPREQUESTs, it’s possible that more

 

than one DHCPACK is returned with a valid Option 66.

 

• Evaluating and updating the configuration file occurs only on the

 

primary VLAN.

 

• Option 66 is ignored by any interfaces not belonging to the primary

 

VLAN.

 

 

Multiple Servers serving a Single VLAN

• Each DHCP-enabled VLAN interface initiates one DHCPDISCOVER

 

and receives one or more DHCPOFFER messages.

 

• Each interface accepts the best offer.

 

• Option 66 is processed only for the interface belonging to the primary

 

VLAN.

 

 

Multiple Servers serving Multiple VLANs

• Each DHSP-enabled VLAN interface initiates DHCPDISCOVER and

 

receives one or more DHCPOFFER messages.

 

• 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 downloads 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)

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