H3C S7500 Series Ethernet Switches Release 3135 DHCP Configuration Examples

DHCP Configuration Examples
H3C S7500 Series Ethernet Switches Release 3135 Chapter 2 Configuration Examples
2-9
IV. Configuring the DHCP server in the HQ
# On the H3C series switches, port numbers, VLAN numbers, and the MAC addresses
of the DHCP snooping device and the DHCP relay agent are added to DHCP Option 82.
A complete piece of Option 82 information is a combination of the values of two
suboptions:
Circuit ID suboption: It identifies the VLAN to which the clients belong and the port to
which the DHCP snooping device is connected.
0 31
Type(1)
15
VLAN ID
Length(6) 0 4
Port Index
Figure 2-6 Packet structure of Circuit ID suboption
For example, the DHCP messages from clients connected to Ethernet 2/0/12 are
added with Option 82, whose Circuit ID suboption should be 0x0106000400010011,
where 01060004 is a fixed value, 0001 indicates the access port’s VLAN is VLAN 1,
and 0011 is the absolute number of the port, which is less than the actual port number
by 1, indicating the actual port is Ethernet 2/0/12.
Remote ID suboption: It identifies the MAC address of the DHCP snooping device
connected to the client.
0 31
Type(2)
15
Bridge MAC Address
Length(8) 0 6
Figure 2-7 Packet structure of Remote ID suboption
For example, the DHCP messages from clients connected to the DHCP snooping
device with MAC 000f-e234-bc66 are added with Option 82, whose Remote ID
suboption should be 02080006000fe234bc66, where 02080006 is a fixed value and
000fe234bc66 is the MAC address of the DHCP snooping device.
In this example, IP addresses are assigned based on port number only. Therefore, on
the DHCP server, only a matching port number field in the Circuit ID suboption needs to
be found.