H3C Technologies H3C WX3000 Series Unified Switches - Manual (Page 317)

31-3
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 34-2 Extended format of the circuit ID sub-option
Suboption type
0 7 15
Length Circuit ID type Length
23 31
VLAN ID Port Index
Figure 34-3 Extended format of the remote ID sub-option
Suboption type
0 7 15
Length Reomte ID type Length
23 31
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 34-4 and Figure 34-5 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 34-4 Standard format of the circuit ID sub-option
Suboption type
0 7 15
Length
23 31
VLAN ID
Port Index
Figure 34-5 Standard format of the remote ID sub-option
Suboption type
0 7 15
Length
23 31
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 34-1 .