Chapter 28 DHCP Snooping
XGS4600 Series User’s Guide
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You can configure the name and location of the file on the external TFTP server. The file has the following
format:
Figure 237 DHCP Snooping Database File Format
The <initial-checksum> helps distinguish between the bindings in the latest update and the bindings
from previous updates. Each binding consists of 72 bytes, a space, and another checksum that is used
to validate the binding when it is read. If the calculated checksum is not equal to the checksum in the
file, that binding and all others after it are ignored.
28.4.1.3 DHCP Relay Option 82 Information
The Switch can add information to DHCP requests that it does not discard. This provides the DHCP server
more information about the source of the requests. The Switch can add the following information:
• Slot ID (1 byte), port ID (1 byte), and source VLAN ID (2 bytes)
• System name (up to 32 bytes)
This information is stored in an Agent Information field in the option 82 field of the DHCP headers of client
DHCP request frames.
When the DHCP server responds, the Switch removes the information in the Agent Information field
before forwarding the response to the original source.
You can configure this setting for each source VLAN. This setting is independent of the DHCP relay
settings.
28.4.1.4 Configuring DHCP Snooping
Follow these steps to configure DHCP snooping on the Switch.
1 Enable DHCP snooping on the Switch.
2 Enable DHCP snooping on each VLAN, and configure DHCP relay option 82.
3 Configure trusted and untrusted ports, and specify the maximum number of DHCP packets that each
port can receive per second.
4 Configure static bindings.
<initial-checksum>
TYPE DHCP-SNOOPING
VERSION 1
BEGIN
<binding-1> <checksum-1>
<binding-2> <checksum-1-2>
...
...
<binding-n> <checksum-1-2-..-n>
END
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