3Com WX3000 operation manual Overview of IP Filtering, Dhcp-snooping information format command or

Table 3-1Ways of handling a DHCP packet with Option 82

Handling	Sub-option		The DHCP snooping device will…
policy	configuration
Drop	—	Drop the packet.
Keep	—		Forward the packet without changing Option 82.
			Forward the packet after replacing the original Option 82 with
	Neither of the two		the default content.
	sub-options is		The storage format of Option 82 content is the one specified with
	configured		the dhcp-snooping information format command or the
			default HEX format if this command is not executed.
Replace
	Circuit ID		Forward the packet after replacing the circuit ID sub-option of
	sub-option is		the original Option 82 with the configured circuit ID sub-option in
	configured		ASCII format.
	Remote ID	Forward the packet after replacing the remote ID sub-option of
	sub-option is	the original Option 82 with the configured remote ID sub-option
	configured	in ASCII format.

When receiving a DHCP client’s request without Option 82, the DHCP snooping device will add the option field with the configured sub-option and then forward the packet. For details, see Table 3-2.

Table 3-2Ways of handling a DHCP packet without Option 82

Sub-option configuration	The DHCP snooping device will…
	Forward the packet after adding Option 82 with the default contents.
Neither of the two	The format of Option 82 is the one specified with the
sub-options is configured.	dhcp-snooping information format command or the default HEX
	format if this command is not executed.
Circuit ID sub-option is	Forward the packet after adding Option 82 with the configured circuit
configured.	ID sub-option in ASCII format.
Remote ID sub-option is	Forward the packet after adding Option 82 with the configured
configured.	remote ID sub-option in ASCII format.

The circuit ID and remote ID sub-options in Option 82, which can be configured simultaneously or separately, are independent of each other in terms of configuration sequence.

When the DHCP snooping device receives a DHCP response packet from the DHCP server, the DHCP snooping device will delete the Option 82 field, if contained, before forwarding the packet, or will directly forward the packet if the packet does not contain the Option 82 field.

Overview of IP Filtering

A denial-of-service (DoS) attack means an attempt of an attacker sending a large number of forged address requests with different source IP addresses to the server so that the network cannot work normally. The specific effects are as follows:

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