Overview Of The Dhcp Snooping Database Agent - Cisco 7604 Configuration Manual

Ios software configuration guide

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Configuring DHCP Snooping

router uses the packet formats when DHCP snooping is globally enabled and when the ip dhcp snooping

information option global configuration command is entered. For the circuit ID suboption, the module

field is the slot number of the module.

Figure 37-2 Suboption Packet Formats

Circuit ID Suboption Frame Format

Remote ID Suboption Frame Format

Overview of the DHCP Snooping Database Agent

To retain the bindings across reloads, you must use the DHCP snooping database agent. Without this

agent, the bindings established by DHCP snooping are lost upon reload, and connectivity is lost as well.

The database agent stores the bindings in a file at a configured location. Upon reload, the router reads

the file to build the database for the bindings. The router keeps the file current by writing to the file as

the database changes.

The format of the file that contains the bindings is as follows:

<initial-checksum>

TYPE DHCP-SNOOPING

<entry-1> <checksum-1>

<entry-2> <checksum-1-2>

<entry-n> <checksum-1-2-..-n>

Each entry in the file is tagged with a checksum that is used to validate the entries whenever the file is

read. The <initial-checksum> entry on the first line helps distinguish entries associated with the latest

write from entries that are associated with a previous write.

shows the packet formats for the remote ID suboption and the circuit ID suboption. The

1 byte 1 byte 1 byte

1 byte 1 byte 1 byte

Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX

1 byte 1 byte

Understanding DHCP Snooping

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7613 7606 7609-s 7600 series