H3C S5100-SI Operation Manual page 357

sub-options (with the default padding 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 3-2 Extended format of the circuit ID sub-option
Figure 3-3 Extended format of the remote ID sub-option
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, S5100-SI/EI Series Ethernet Switches support
Option 82 in the standard format. Refer to
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 3-4 Standard format of the circuit ID sub-option
Figure 3-5 Standard format of the remote ID sub-option
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 Ways of handling a DHCP packet with Option 82
Handling policy
Drop
Figure 3-4
Sub-option configuration
—
3-3
and Figure 3-5 for the standard format of the
Table
The DHCP Snooping device will...
Drop the packet.
3-1.