H3C Technologies H3C S3600 Series Switches - Manual (Page 686)

4-3
Figure 4-3 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, S3600 Series Ethernet Switches support
Option 82 in the standard format. Refer to Figure 4-4 and Figure 4-5 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 4-4 Standard format of the circuit ID sub-option
Figure 4-5 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 4-1 .
Table 4-1 Ways of handling a DHCP packet with Option 82
Handling policy Sub-option configuration
The DHCP Snooping device
will…
Drop — Drop the packet.
Keep —
Forward the packet without
changing Option 82.
Replace
Neither of the two sub-options
is configured
Forward the packet after
replacing the original Option 82
with the default content.
The storage format of Option
82 content is the one specified
with the dhcp-snooping
information format command
or the default HEX format if this
command is not executed.