3Com 7757 Configuration Manual page 626

626 C 59: DHCP S
HAPTER
n
C
NOOPING ONFIGURATION
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 495.
Table 495 Ways of handling a DHCP packet with Option 82
Handling Sub-option
policy configuration
Drop -
Keep -
Replace Neither of the two
sub-options is
configured
Circuit ID
sub-option is
configured
Remote ID
sub-option is
configured
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 496.
Table 496 Ways of handling a DHCP packet without Option 82
Sub-option
configuration
Neither of the two
sub-options is configured.
Circuit ID sub-option is
configured.
Remote ID sub-option is
configured.
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.
Upon receiving a packet returned by the DHCP server, the DHCP snooping device
checks the Option 82 field:
If it was added by the local device, the device strips off Option 82 and forwards
■
the packet to the DHCP client.
If it was not added by the local device, the device obtains the VLAN
■
information in Option 82 and broadcasts this packet within the VLAN.
The DHCP Snooping device will...
Drop the packet.
Forward the packet without changing Option 82.
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.
Forward the packet after replacing the circuit ID
sub-option of the original Option 82 with the
configured circuit ID sub-option in ASCII format.
Forward the packet after replacing the remote ID
sub-option of the original Option 82 with the
configured remote ID sub-option in ASCII format.
The DHCP-Snooping device will ...
Forward the packet after adding Option 82 with the default
contents.
The format of Option 82 is the one specified with the
dhcp-snooping information format command or the default
HEX format if this command is not executed.
Forward the packet after adding Option 82 with the configured
circuit ID sub-option in ASCII format.
Forward the packet after adding Option 82 with the configured
remote ID sub-option in ASCII format.