Operation Manual – DHCP
H3C S5600 Series Ethernet Switches
Chapter 3 DHCP Relay Agent Configuration
3-3
sub-options of Option 82 are padded as follows, as shown in
Figure 3-2
and
Figure 3-3
.
(The content in brackets is the fixed value of each field.)
z
sub-option 1: Padded with the port index (smaller than the physical port number by
1) and VLAN ID of the port that received the client’s request.
z
sub-option 2: Padded with the bridge MAC address of the DHCP relay agent
device that received the client’s request.
Figure 3-2
Padding contents for sub-option 1 of Option 82
Figure 3-3
Padding contents for sub-option 2 of Option 82
III. Mechanism of Option 82 supported on DHCP relay agent
The procedure for a DHCP client to obtain an IP address from a DHCP server through a
DHCP relay agent is similar to that for the client to obtain an IP address from a DHCP
server directly. The following are the mechanism of Option 82 support on DHCP relay
agent.
1) Upon receiving a DHCP request, the DHCP relay agent checks whether the
packet contains Option 82 and processes the packet accordingly.
z
If the request packet contains Option 82, the DHCP relay agent processes the
packet depending on the configured strategy (that is, discards the packet,
replaces the original Option 82 in the packet with its own, or leaves the original
Option 82 unchanged in the packet), and forwards the packet (if not discarded) to
the DHCP server.
z
If the request packet does not contain Option 82, the DHCP relay agent adds
Option 82 to the packet and forwards the packet to the DHCP server.
2)
Upon receiving the packet returned from the DHCP server, the DHCP relay agent
strips Option 82 from the packet and forwards the packet with the DHCP
configuration information to the DHCP client.
