3Com WX3000 Mechanism of DHCP-snooping Option, 2Extended format of the circuit ID sub-option

contents). That is, the circuit ID or remote ID sub-option defines the type and length of a circuit ID or remote ID.

The remote ID type field and circuit ID type field are determined by the option storage format. They are both set to “0” in the case of HEX format and to “1” in the case of ASCII format.

Figure 3-2Extended format of the circuit ID sub-option

0	7	15	23	31
	Suboption type	Length	Circuit ID type	Length
	VLAN ID		Port Index

Figure 3-3Extended format of the remote ID sub-option

0	7	15	23	31
	Suboption type	Length	Reomte ID type	Length
		Bridge MAC Address

In practice, some network devices do not support the type and length identifiers of the Circuit ID and Remote ID sub-options. To interwork with these devices, the device supports Option 82 in the standard format. Refer to Figure 3-4 and Figure 3-5 for the standard format of the sub-options (with the default padding contents). In the standard format, the Circuit ID or Remote ID sub-option does not contain the two-byte type and length fields of the circuit ID or remote ID.

Figure 3-4Standard format of the circuit ID sub-option

0	7	15	23	31
	Suboption type	Length	VLAN ID
	Port Index

Figure 3-5Standard format of the remote ID sub-option

0	7	15	23	31
	Suboption type	Length
		Bridge MAC Address

Mechanism of DHCP-snooping Option 82

With DHCP snooping and DHCP-snooping Option 82 support enabled, when the DHCP snooping device receives a DHCP client’s request containing Option 82, it will handle the packet according to the handling policy and the configured contents in sub-options. For details, see Table 3-1.

3-3