Configuring DHCP Service Configuration Examples
User Guide    425
Switch#show ip dhcp relay information interface
Interface Option82 Status   Operation Strategy   Format   Circuit ID                         ...
---------    ----------------         ------------------           -------      ---------                            ...
Gi1/0/1     Enable                      Replace                          Normal    Default:VLAN-PORT   ...
Gi1/0/2     Enable                      Replace                          Normal    Default:VLAN-PORT   ...
...
4.2.4  Configuring the DHCP Server
Note:
 •
Make sure the DHCP server supports Option82 and more than one DHCP address pool.
 •
To make sure the DHCP server can reach the computers, you can create static routes or enable 
dynamic routing protocol like RIP on the DHCP server.
 •
In this section, we use different notations to distinguish ASCII strings from hexadecimal 
numbers. An ASCII string is enclosed with quotation marks, such as “123”, while a hexadecimal 
number is divided by colon into parts of two digits, such as 31:32:33.
On the DHCP server, you need to create two DHCP classes to identify the Option 82 
payloads of DHCP request packets from Group 1 and Group 2, respectively. 
In this example, the DHCP relay agent uses the default circuit ID and remote ID in TLV 
format. According to packet formats described in Table 1-1 and Table 1-2, the sub-options 
of the two groups are as shown in the following table.
Table 4-1  Sub-options of Group1 and Group 2
Group Sub-option Type (Hex) Length (Hex) Value (Hex)
1
Circuit ID 00 04 00:02:00:01
Remote ID 00 06 00:00:FF:FF:27:12
2
Circuit ID 00 04 00:02:00:02
Remote ID 00 06 00:00:FF:FF:27:12
The configuration file /etc/dhcpd.conf of the Linux ISC DHCP Server is:
ddns-update-style interim; 
ignore client-updates; 
 
# Create two classes to match the pattern of Option82 in DHCP request packets from   
# Group1 and Group 2, respectively. 
# The agent circuit ID inserted by the DHCP relay switch is 6 bytes long in TLV format, one  
# byte for Type, one byte for Length, and 4 bytes for Value. Therefore, the offset is 2 and the 
length is 4. 
Downloaded from ManualsNet.com search engine