ZyXEL GS2200-8 User Guide - Page 212

DHCP Snooping Database, 10.1.3, DHCP Relay Option 82 Information

Page 212 highlights

Chapter 25 IP Source Guard 25.10.1.2 DHCP Snooping Database The Switch stores the binding table in volatile memory. If the Switch restarts, it loads static bindings from permanent memory but loses the dynamic bindings, in which case the devices in the network have to send DHCP requests again. As a result, it is recommended you configure the DHCP snooping database. The DHCP snooping database maintains the dynamic bindings for DHCP snooping and ARP inspection in a file on an external TFTP server. If you set up the DHCP snooping database, the Switch can reload the dynamic bindings from the DHCP snooping database after the Switch restarts. You can configure the name and location of the file on the external TFTP server. The file has the following format: Figure 132 DHCP Snooping Database File Format TYPE DHCP-SNOOPING VERSION 1 BEGIN ... ... END The 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. 25.10.1.3 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. See Chapter 32 on page 244 for more information about DHCP relay option 82. 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 (Chapter 32 on page 244). 212 GS2200-8/24 User's Guide

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Chapter 25 IP Source Guard
GS2200-8/24 User’s Guide
212
25.10.1.2
DHCP Snooping Database
The Switch stores the binding table in volatile memory. If the Switch restarts, it loads static
bindings from permanent memory but loses the dynamic bindings, in which case the devices in the
network have to send DHCP requests again. As a result, it is recommended you configure the DHCP
snooping database.
The DHCP snooping database maintains the dynamic bindings for DHCP snooping and ARP
inspection in a file on an external TFTP server. If you set up the DHCP snooping database, the
Switch can reload the dynamic bindings from the DHCP snooping database after the Switch
restarts.
You can configure the name and location of the file on the external TFTP server. The file has the
following format:
Figure 132
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.
25.10.1.3
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. See
Chapter 32 on page 244
for more information about DHCP relay
option 82.
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 (
Chapter 32 on page 244
).
<initial-checksum>
TYPE DHCP-SNOOPING
VERSION 1
BEGIN
<binding-1> <checksum-1>
<binding-2> <checksum-1-2>
...
...
<binding-n> <checksum-1-2-..-n>
END